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rust: syn: import crate

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This is a subset of the Rust `syn` crate, version 2.0.106 (released
2025-08-16), licensed under "Apache-2.0 OR MIT", from:

    https://github.com/dtolnay/syn/raw/2.0.106/src

The files are copied as-is, with no modifications whatsoever (not even
adding the SPDX identifiers).

For copyright details, please see:

    https://github.com/dtolnay/syn/blob/2.0.106/README.md#license
    https://github.com/dtolnay/syn/blob/2.0.106/LICENSE-APACHE
    https://github.com/dtolnay/syn/blob/2.0.106/LICENSE-MIT

The next two patches modify these files as needed for use within the
kernel. This patch split allows reviewers to double-check the import
and to clearly see the differences introduced.

The following script may be used to verify the contents:

    for path in $(cd rust/syn/ && find . -type f -name '*.rs'); do
        curl --silent --show-error --location \
            https://github.com/dtolnay/syn/raw/2.0.106/src/$path \
            | diff --unified rust/syn/$path - && echo $path: OK
    done

Reviewed-by: Gary Guo <gary@garyguo.net>
Tested-by: Gary Guo <gary@garyguo.net>
Tested-by: Jesung Yang <y.j3ms.n@gmail.com>
Link: https://patch.msgid.link/20251124151837.2184382-16-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Miguel Ojeda
2025-11-24 16:18:27 +01:00
parent 88de91cc1c
commit 808c999fc9
55 changed files with 49824 additions and 0 deletions
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836
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#[cfg(feature = "parsing")]
use crate::error::Error;
#[cfg(feature = "parsing")]
use crate::error::Result;
use crate::expr::Expr;
use crate::mac::MacroDelimiter;
#[cfg(feature = "parsing")]
use crate::meta::{self, ParseNestedMeta};
#[cfg(feature = "parsing")]
use crate::parse::{Parse, ParseStream, Parser};
use crate::path::Path;
use crate::token;
use proc_macro2::TokenStream;
#[cfg(feature = "printing")]
use std::iter;
#[cfg(feature = "printing")]
use std::slice;
ast_struct! {
/// An attribute, like `#[repr(transparent)]`.
///
/// <br>
///
/// # Syntax
///
/// Rust has six types of attributes.
///
/// - Outer attributes like `#[repr(transparent)]`. These appear outside or
/// in front of the item they describe.
///
/// - Inner attributes like `#![feature(proc_macro)]`. These appear inside
/// of the item they describe, usually a module.
///
/// - Outer one-line doc comments like `/// Example`.
///
/// - Inner one-line doc comments like `//! Please file an issue`.
///
/// - Outer documentation blocks `/** Example */`.
///
/// - Inner documentation blocks `/*! Please file an issue */`.
///
/// The `style` field of type `AttrStyle` distinguishes whether an attribute
/// is outer or inner.
///
/// Every attribute has a `path` that indicates the intended interpretation
/// of the rest of the attribute's contents. The path and the optional
/// additional contents are represented together in the `meta` field of the
/// attribute in three possible varieties:
///
/// - Meta::Path &mdash; attributes whose information content conveys just a
/// path, for example the `#[test]` attribute.
///
/// - Meta::List &mdash; attributes that carry arbitrary tokens after the
/// path, surrounded by a delimiter (parenthesis, bracket, or brace). For
/// example `#[derive(Copy)]` or `#[precondition(x < 5)]`.
///
/// - Meta::NameValue &mdash; attributes with an `=` sign after the path,
/// followed by a Rust expression. For example `#[path =
/// "sys/windows.rs"]`.
///
/// All doc comments are represented in the NameValue style with a path of
/// "doc", as this is how they are processed by the compiler and by
/// `macro_rules!` macros.
///
/// ```text
/// #[derive(Copy, Clone)]
/// ~~~~~~Path
/// ^^^^^^^^^^^^^^^^^^^Meta::List
///
/// #[path = "sys/windows.rs"]
/// ~~~~Path
/// ^^^^^^^^^^^^^^^^^^^^^^^Meta::NameValue
///
/// #[test]
/// ^^^^Meta::Path
/// ```
///
/// <br>
///
/// # Parsing from tokens to Attribute
///
/// This type does not implement the [`Parse`] trait and thus cannot be
/// parsed directly by [`ParseStream::parse`]. Instead use
/// [`ParseStream::call`] with one of the two parser functions
/// [`Attribute::parse_outer`] or [`Attribute::parse_inner`] depending on
/// which you intend to parse.
///
/// [`Parse`]: crate::parse::Parse
/// [`ParseStream::parse`]: crate::parse::ParseBuffer::parse
/// [`ParseStream::call`]: crate::parse::ParseBuffer::call
///
/// ```
/// use syn::{Attribute, Ident, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Parses a unit struct with attributes.
/// //
/// // #[path = "s.tmpl"]
/// // struct S;
/// struct UnitStruct {
/// attrs: Vec<Attribute>,
/// struct_token: Token![struct],
/// name: Ident,
/// semi_token: Token![;],
/// }
///
/// impl Parse for UnitStruct {
/// fn parse(input: ParseStream) -> Result<Self> {
/// Ok(UnitStruct {
/// attrs: input.call(Attribute::parse_outer)?,
/// struct_token: input.parse()?,
/// name: input.parse()?,
/// semi_token: input.parse()?,
/// })
/// }
/// }
/// ```
///
/// <p><br></p>
///
/// # Parsing from Attribute to structured arguments
///
/// The grammar of attributes in Rust is very flexible, which makes the
/// syntax tree not that useful on its own. In particular, arguments of the
/// `Meta::List` variety of attribute are held in an arbitrary `tokens:
/// TokenStream`. Macros are expected to check the `path` of the attribute,
/// decide whether they recognize it, and then parse the remaining tokens
/// according to whatever grammar they wish to require for that kind of
/// attribute. Use [`parse_args()`] to parse those tokens into the expected
/// data structure.
///
/// [`parse_args()`]: Attribute::parse_args
///
/// <p><br></p>
///
/// # Doc comments
///
/// The compiler transforms doc comments, such as `/// comment` and `/*!
/// comment */`, into attributes before macros are expanded. Each comment is
/// expanded into an attribute of the form `#[doc = r"comment"]`.
///
/// As an example, the following `mod` items are expanded identically:
///
/// ```
/// # use syn::{ItemMod, parse_quote};
/// let doc: ItemMod = parse_quote! {
/// /// Single line doc comments
/// /// We write so many!
/// /**
/// * Multi-line comments...
/// * May span many lines
/// */
/// mod example {
/// //! Of course, they can be inner too
/// /*! And fit in a single line */
/// }
/// };
/// let attr: ItemMod = parse_quote! {
/// #[doc = r" Single line doc comments"]
/// #[doc = r" We write so many!"]
/// #[doc = r"
/// * Multi-line comments...
/// * May span many lines
/// "]
/// mod example {
/// #![doc = r" Of course, they can be inner too"]
/// #![doc = r" And fit in a single line "]
/// }
/// };
/// assert_eq!(doc, attr);
/// ```
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct Attribute {
pub pound_token: Token![#],
pub style: AttrStyle,
pub bracket_token: token::Bracket,
pub meta: Meta,
}
}
impl Attribute {
/// Returns the path that identifies the interpretation of this attribute.
///
/// For example this would return the `test` in `#[test]`, the `derive` in
/// `#[derive(Copy)]`, and the `path` in `#[path = "sys/windows.rs"]`.
pub fn path(&self) -> &Path {
self.meta.path()
}
/// Parse the arguments to the attribute as a syntax tree.
///
/// This is similar to pulling out the `TokenStream` from `Meta::List` and
/// doing `syn::parse2::<T>(meta_list.tokens)`, except that using
/// `parse_args` the error message has a more useful span when `tokens` is
/// empty.
///
/// The surrounding delimiters are *not* included in the input to the
/// parser.
///
/// ```text
/// #[my_attr(value < 5)]
/// ^^^^^^^^^ what gets parsed
/// ```
///
/// # Example
///
/// ```
/// use syn::{parse_quote, Attribute, Expr};
///
/// let attr: Attribute = parse_quote! {
/// #[precondition(value < 5)]
/// };
///
/// if attr.path().is_ident("precondition") {
/// let precondition: Expr = attr.parse_args()?;
/// // ...
/// }
/// # anyhow::Ok(())
/// ```
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_args<T: Parse>(&self) -> Result<T> {
self.parse_args_with(T::parse)
}
/// Parse the arguments to the attribute using the given parser.
///
/// # Example
///
/// ```
/// use syn::{parse_quote, Attribute};
///
/// let attr: Attribute = parse_quote! {
/// #[inception { #[brrrrrrraaaaawwwwrwrrrmrmrmmrmrmmmmm] }]
/// };
///
/// let bwom = attr.parse_args_with(Attribute::parse_outer)?;
///
/// // Attribute does not have a Parse impl, so we couldn't directly do:
/// // let bwom: Attribute = attr.parse_args()?;
/// # anyhow::Ok(())
/// ```
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_args_with<F: Parser>(&self, parser: F) -> Result<F::Output> {
match &self.meta {
Meta::Path(path) => Err(crate::error::new2(
path.segments.first().unwrap().ident.span(),
path.segments.last().unwrap().ident.span(),
format!(
"expected attribute arguments in parentheses: {}[{}(...)]",
parsing::DisplayAttrStyle(&self.style),
parsing::DisplayPath(path),
),
)),
Meta::NameValue(meta) => Err(Error::new(
meta.eq_token.span,
format_args!(
"expected parentheses: {}[{}(...)]",
parsing::DisplayAttrStyle(&self.style),
parsing::DisplayPath(&meta.path),
),
)),
Meta::List(meta) => meta.parse_args_with(parser),
}
}
/// Parse the arguments to the attribute, expecting it to follow the
/// conventional structure used by most of Rust's built-in attributes.
///
/// The [*Meta Item Attribute Syntax*][syntax] section in the Rust reference
/// explains the convention in more detail. Not all attributes follow this
/// convention, so [`parse_args()`][Self::parse_args] is available if you
/// need to parse arbitrarily goofy attribute syntax.
///
/// [syntax]: https://doc.rust-lang.org/reference/attributes.html#meta-item-attribute-syntax
///
/// # Example
///
/// We'll parse a struct, and then parse some of Rust's `#[repr]` attribute
/// syntax.
///
/// ```
/// use syn::{parenthesized, parse_quote, token, ItemStruct, LitInt};
///
/// let input: ItemStruct = parse_quote! {
/// #[repr(C, align(4))]
/// pub struct MyStruct(u16, u32);
/// };
///
/// let mut repr_c = false;
/// let mut repr_transparent = false;
/// let mut repr_align = None::<usize>;
/// let mut repr_packed = None::<usize>;
/// for attr in &input.attrs {
/// if attr.path().is_ident("repr") {
/// attr.parse_nested_meta(|meta| {
/// // #[repr(C)]
/// if meta.path.is_ident("C") {
/// repr_c = true;
/// return Ok(());
/// }
///
/// // #[repr(transparent)]
/// if meta.path.is_ident("transparent") {
/// repr_transparent = true;
/// return Ok(());
/// }
///
/// // #[repr(align(N))]
/// if meta.path.is_ident("align") {
/// let content;
/// parenthesized!(content in meta.input);
/// let lit: LitInt = content.parse()?;
/// let n: usize = lit.base10_parse()?;
/// repr_align = Some(n);
/// return Ok(());
/// }
///
/// // #[repr(packed)] or #[repr(packed(N))], omitted N means 1
/// if meta.path.is_ident("packed") {
/// if meta.input.peek(token::Paren) {
/// let content;
/// parenthesized!(content in meta.input);
/// let lit: LitInt = content.parse()?;
/// let n: usize = lit.base10_parse()?;
/// repr_packed = Some(n);
/// } else {
/// repr_packed = Some(1);
/// }
/// return Ok(());
/// }
///
/// Err(meta.error("unrecognized repr"))
/// })?;
/// }
/// }
/// # anyhow::Ok(())
/// ```
///
/// # Alternatives
///
/// In some cases, for attributes which have nested layers of structured
/// content, the following less flexible approach might be more convenient:
///
/// ```
/// # use syn::{parse_quote, ItemStruct};
/// #
/// # let input: ItemStruct = parse_quote! {
/// # #[repr(C, align(4))]
/// # pub struct MyStruct(u16, u32);
/// # };
/// #
/// use syn::punctuated::Punctuated;
/// use syn::{parenthesized, token, Error, LitInt, Meta, Token};
///
/// let mut repr_c = false;
/// let mut repr_transparent = false;
/// let mut repr_align = None::<usize>;
/// let mut repr_packed = None::<usize>;
/// for attr in &input.attrs {
/// if attr.path().is_ident("repr") {
/// let nested = attr.parse_args_with(Punctuated::<Meta, Token![,]>::parse_terminated)?;
/// for meta in nested {
/// match meta {
/// // #[repr(C)]
/// Meta::Path(path) if path.is_ident("C") => {
/// repr_c = true;
/// }
///
/// // #[repr(align(N))]
/// Meta::List(meta) if meta.path.is_ident("align") => {
/// let lit: LitInt = meta.parse_args()?;
/// let n: usize = lit.base10_parse()?;
/// repr_align = Some(n);
/// }
///
/// /* ... */
///
/// _ => {
/// return Err(Error::new_spanned(meta, "unrecognized repr"));
/// }
/// }
/// }
/// }
/// }
/// # Ok(())
/// ```
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_nested_meta(
&self,
logic: impl FnMut(ParseNestedMeta) -> Result<()>,
) -> Result<()> {
self.parse_args_with(meta::parser(logic))
}
/// Parses zero or more outer attributes from the stream.
///
/// # Example
///
/// See
/// [*Parsing from tokens to Attribute*](#parsing-from-tokens-to-attribute).
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_outer(input: ParseStream) -> Result<Vec<Self>> {
let mut attrs = Vec::new();
while input.peek(Token![#]) {
attrs.push(input.call(parsing::single_parse_outer)?);
}
Ok(attrs)
}
/// Parses zero or more inner attributes from the stream.
///
/// # Example
///
/// See
/// [*Parsing from tokens to Attribute*](#parsing-from-tokens-to-attribute).
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_inner(input: ParseStream) -> Result<Vec<Self>> {
let mut attrs = Vec::new();
parsing::parse_inner(input, &mut attrs)?;
Ok(attrs)
}
}
ast_enum! {
/// Distinguishes between attributes that decorate an item and attributes
/// that are contained within an item.
///
/// # Outer attributes
///
/// - `#[repr(transparent)]`
/// - `/// # Example`
/// - `/** Please file an issue */`
///
/// # Inner attributes
///
/// - `#![feature(proc_macro)]`
/// - `//! # Example`
/// - `/*! Please file an issue */`
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub enum AttrStyle {
Outer,
Inner(Token![!]),
}
}
ast_enum! {
/// Content of a compile-time structured attribute.
///
/// ## Path
///
/// A meta path is like the `test` in `#[test]`.
///
/// ## List
///
/// A meta list is like the `derive(Copy)` in `#[derive(Copy)]`.
///
/// ## NameValue
///
/// A name-value meta is like the `path = "..."` in `#[path =
/// "sys/windows.rs"]`.
///
/// # Syntax tree enum
///
/// This type is a [syntax tree enum].
///
/// [syntax tree enum]: crate::expr::Expr#syntax-tree-enums
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub enum Meta {
Path(Path),
/// A structured list within an attribute, like `derive(Copy, Clone)`.
List(MetaList),
/// A name-value pair within an attribute, like `feature = "nightly"`.
NameValue(MetaNameValue),
}
}
ast_struct! {
/// A structured list within an attribute, like `derive(Copy, Clone)`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct MetaList {
pub path: Path,
pub delimiter: MacroDelimiter,
pub tokens: TokenStream,
}
}
ast_struct! {
/// A name-value pair within an attribute, like `feature = "nightly"`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct MetaNameValue {
pub path: Path,
pub eq_token: Token![=],
pub value: Expr,
}
}
impl Meta {
/// Returns the path that begins this structured meta item.
///
/// For example this would return the `test` in `#[test]`, the `derive` in
/// `#[derive(Copy)]`, and the `path` in `#[path = "sys/windows.rs"]`.
pub fn path(&self) -> &Path {
match self {
Meta::Path(path) => path,
Meta::List(meta) => &meta.path,
Meta::NameValue(meta) => &meta.path,
}
}
/// Error if this is a `Meta::List` or `Meta::NameValue`.
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn require_path_only(&self) -> Result<&Path> {
let error_span = match self {
Meta::Path(path) => return Ok(path),
Meta::List(meta) => meta.delimiter.span().open(),
Meta::NameValue(meta) => meta.eq_token.span,
};
Err(Error::new(error_span, "unexpected token in attribute"))
}
/// Error if this is a `Meta::Path` or `Meta::NameValue`.
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn require_list(&self) -> Result<&MetaList> {
match self {
Meta::List(meta) => Ok(meta),
Meta::Path(path) => Err(crate::error::new2(
path.segments.first().unwrap().ident.span(),
path.segments.last().unwrap().ident.span(),
format!(
"expected attribute arguments in parentheses: `{}(...)`",
parsing::DisplayPath(path),
),
)),
Meta::NameValue(meta) => Err(Error::new(meta.eq_token.span, "expected `(`")),
}
}
/// Error if this is a `Meta::Path` or `Meta::List`.
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn require_name_value(&self) -> Result<&MetaNameValue> {
match self {
Meta::NameValue(meta) => Ok(meta),
Meta::Path(path) => Err(crate::error::new2(
path.segments.first().unwrap().ident.span(),
path.segments.last().unwrap().ident.span(),
format!(
"expected a value for this attribute: `{} = ...`",
parsing::DisplayPath(path),
),
)),
Meta::List(meta) => Err(Error::new(meta.delimiter.span().open(), "expected `=`")),
}
}
}
impl MetaList {
/// See [`Attribute::parse_args`].
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_args<T: Parse>(&self) -> Result<T> {
self.parse_args_with(T::parse)
}
/// See [`Attribute::parse_args_with`].
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_args_with<F: Parser>(&self, parser: F) -> Result<F::Output> {
let scope = self.delimiter.span().close();
crate::parse::parse_scoped(parser, scope, self.tokens.clone())
}
/// See [`Attribute::parse_nested_meta`].
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_nested_meta(
&self,
logic: impl FnMut(ParseNestedMeta) -> Result<()>,
) -> Result<()> {
self.parse_args_with(meta::parser(logic))
}
}
#[cfg(feature = "printing")]
pub(crate) trait FilterAttrs<'a> {
type Ret: Iterator<Item = &'a Attribute>;
fn outer(self) -> Self::Ret;
#[cfg(feature = "full")]
fn inner(self) -> Self::Ret;
}
#[cfg(feature = "printing")]
impl<'a> FilterAttrs<'a> for &'a [Attribute] {
type Ret = iter::Filter<slice::Iter<'a, Attribute>, fn(&&Attribute) -> bool>;
fn outer(self) -> Self::Ret {
fn is_outer(attr: &&Attribute) -> bool {
match attr.style {
AttrStyle::Outer => true,
AttrStyle::Inner(_) => false,
}
}
self.iter().filter(is_outer)
}
#[cfg(feature = "full")]
fn inner(self) -> Self::Ret {
fn is_inner(attr: &&Attribute) -> bool {
match attr.style {
AttrStyle::Inner(_) => true,
AttrStyle::Outer => false,
}
}
self.iter().filter(is_inner)
}
}
impl From<Path> for Meta {
fn from(meta: Path) -> Meta {
Meta::Path(meta)
}
}
impl From<MetaList> for Meta {
fn from(meta: MetaList) -> Meta {
Meta::List(meta)
}
}
impl From<MetaNameValue> for Meta {
fn from(meta: MetaNameValue) -> Meta {
Meta::NameValue(meta)
}
}
#[cfg(feature = "parsing")]
pub(crate) mod parsing {
use crate::attr::{AttrStyle, Attribute, Meta, MetaList, MetaNameValue};
use crate::error::Result;
use crate::expr::{Expr, ExprLit};
use crate::lit::Lit;
use crate::parse::discouraged::Speculative as _;
use crate::parse::{Parse, ParseStream};
use crate::path::Path;
use crate::{mac, token};
use proc_macro2::Ident;
use std::fmt::{self, Display};
pub(crate) fn parse_inner(input: ParseStream, attrs: &mut Vec<Attribute>) -> Result<()> {
while input.peek(Token![#]) && input.peek2(Token![!]) {
attrs.push(input.call(single_parse_inner)?);
}
Ok(())
}
pub(crate) fn single_parse_inner(input: ParseStream) -> Result<Attribute> {
let content;
Ok(Attribute {
pound_token: input.parse()?,
style: AttrStyle::Inner(input.parse()?),
bracket_token: bracketed!(content in input),
meta: content.parse()?,
})
}
pub(crate) fn single_parse_outer(input: ParseStream) -> Result<Attribute> {
let content;
Ok(Attribute {
pound_token: input.parse()?,
style: AttrStyle::Outer,
bracket_token: bracketed!(content in input),
meta: content.parse()?,
})
}
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for Meta {
fn parse(input: ParseStream) -> Result<Self> {
let path = parse_outermost_meta_path(input)?;
parse_meta_after_path(path, input)
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for MetaList {
fn parse(input: ParseStream) -> Result<Self> {
let path = parse_outermost_meta_path(input)?;
parse_meta_list_after_path(path, input)
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for MetaNameValue {
fn parse(input: ParseStream) -> Result<Self> {
let path = parse_outermost_meta_path(input)?;
parse_meta_name_value_after_path(path, input)
}
}
// Unlike meta::parse_meta_path which accepts arbitrary keywords in the path,
// only the `unsafe` keyword is accepted as an attribute's outermost path.
fn parse_outermost_meta_path(input: ParseStream) -> Result<Path> {
if input.peek(Token![unsafe]) {
let unsafe_token: Token![unsafe] = input.parse()?;
Ok(Path::from(Ident::new("unsafe", unsafe_token.span)))
} else {
Path::parse_mod_style(input)
}
}
pub(crate) fn parse_meta_after_path(path: Path, input: ParseStream) -> Result<Meta> {
if input.peek(token::Paren) || input.peek(token::Bracket) || input.peek(token::Brace) {
parse_meta_list_after_path(path, input).map(Meta::List)
} else if input.peek(Token![=]) {
parse_meta_name_value_after_path(path, input).map(Meta::NameValue)
} else {
Ok(Meta::Path(path))
}
}
fn parse_meta_list_after_path(path: Path, input: ParseStream) -> Result<MetaList> {
let (delimiter, tokens) = mac::parse_delimiter(input)?;
Ok(MetaList {
path,
delimiter,
tokens,
})
}
fn parse_meta_name_value_after_path(path: Path, input: ParseStream) -> Result<MetaNameValue> {
let eq_token: Token![=] = input.parse()?;
let ahead = input.fork();
let lit: Option<Lit> = ahead.parse()?;
let value = if let (Some(lit), true) = (lit, ahead.is_empty()) {
input.advance_to(&ahead);
Expr::Lit(ExprLit {
attrs: Vec::new(),
lit,
})
} else if input.peek(Token![#]) && input.peek2(token::Bracket) {
return Err(input.error("unexpected attribute inside of attribute"));
} else {
input.parse()?
};
Ok(MetaNameValue {
path,
eq_token,
value,
})
}
pub(super) struct DisplayAttrStyle<'a>(pub &'a AttrStyle);
impl<'a> Display for DisplayAttrStyle<'a> {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
formatter.write_str(match self.0 {
AttrStyle::Outer => "#",
AttrStyle::Inner(_) => "#!",
})
}
}
pub(super) struct DisplayPath<'a>(pub &'a Path);
impl<'a> Display for DisplayPath<'a> {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
for (i, segment) in self.0.segments.iter().enumerate() {
if i > 0 || self.0.leading_colon.is_some() {
formatter.write_str("::")?;
}
write!(formatter, "{}", segment.ident)?;
}
Ok(())
}
}
}
#[cfg(feature = "printing")]
mod printing {
use crate::attr::{AttrStyle, Attribute, Meta, MetaList, MetaNameValue};
use crate::path;
use crate::path::printing::PathStyle;
use proc_macro2::TokenStream;
use quote::ToTokens;
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for Attribute {
fn to_tokens(&self, tokens: &mut TokenStream) {
self.pound_token.to_tokens(tokens);
if let AttrStyle::Inner(b) = &self.style {
b.to_tokens(tokens);
}
self.bracket_token.surround(tokens, |tokens| {
self.meta.to_tokens(tokens);
});
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for Meta {
fn to_tokens(&self, tokens: &mut TokenStream) {
match self {
Meta::Path(path) => path::printing::print_path(tokens, path, PathStyle::Mod),
Meta::List(meta_list) => meta_list.to_tokens(tokens),
Meta::NameValue(meta_name_value) => meta_name_value.to_tokens(tokens),
}
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for MetaList {
fn to_tokens(&self, tokens: &mut TokenStream) {
path::printing::print_path(tokens, &self.path, PathStyle::Mod);
self.delimiter.surround(tokens, self.tokens.clone());
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for MetaNameValue {
fn to_tokens(&self, tokens: &mut TokenStream) {
path::printing::print_path(tokens, &self.path, PathStyle::Mod);
self.eq_token.to_tokens(tokens);
self.value.to_tokens(tokens);
}
}
}

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use std::ops::{AddAssign, MulAssign};
// For implementing base10_digits() accessor on LitInt.
pub(crate) struct BigInt {
digits: Vec<u8>,
}
impl BigInt {
pub(crate) fn new() -> Self {
BigInt { digits: Vec::new() }
}
pub(crate) fn to_string(&self) -> String {
let mut repr = String::with_capacity(self.digits.len());
let mut has_nonzero = false;
for digit in self.digits.iter().rev() {
has_nonzero |= *digit != 0;
if has_nonzero {
repr.push((*digit + b'0') as char);
}
}
if repr.is_empty() {
repr.push('0');
}
repr
}
fn reserve_two_digits(&mut self) {
let len = self.digits.len();
let desired =
len + !self.digits.ends_with(&[0, 0]) as usize + !self.digits.ends_with(&[0]) as usize;
self.digits.resize(desired, 0);
}
}
impl AddAssign<u8> for BigInt {
// Assumes increment <16.
fn add_assign(&mut self, mut increment: u8) {
self.reserve_two_digits();
let mut i = 0;
while increment > 0 {
let sum = self.digits[i] + increment;
self.digits[i] = sum % 10;
increment = sum / 10;
i += 1;
}
}
}
impl MulAssign<u8> for BigInt {
// Assumes base <=16.
fn mul_assign(&mut self, base: u8) {
self.reserve_two_digits();
let mut carry = 0;
for digit in &mut self.digits {
let prod = *digit * base + carry;
*digit = prod % 10;
carry = prod / 10;
}
}
}

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//! A stably addressed token buffer supporting efficient traversal based on a
//! cheaply copyable cursor.
// This module is heavily commented as it contains most of the unsafe code in
// Syn, and caution should be used when editing it. The public-facing interface
// is 100% safe but the implementation is fragile internally.
use crate::Lifetime;
use proc_macro2::extra::DelimSpan;
use proc_macro2::{Delimiter, Group, Ident, Literal, Punct, Spacing, Span, TokenStream, TokenTree};
use std::cmp::Ordering;
use std::marker::PhantomData;
use std::ptr;
/// Internal type which is used instead of `TokenTree` to represent a token tree
/// within a `TokenBuffer`.
enum Entry {
// Mimicking types from proc-macro.
// Group entries contain the offset to the matching End entry.
Group(Group, usize),
Ident(Ident),
Punct(Punct),
Literal(Literal),
// End entries contain the offset (negative) to the start of the buffer, and
// offset (negative) to the matching Group entry.
End(isize, isize),
}
/// A buffer that can be efficiently traversed multiple times, unlike
/// `TokenStream` which requires a deep copy in order to traverse more than
/// once.
pub struct TokenBuffer {
// NOTE: Do not implement clone on this - while the current design could be
// cloned, other designs which could be desirable may not be cloneable.
entries: Box<[Entry]>,
}
impl TokenBuffer {
fn recursive_new(entries: &mut Vec<Entry>, stream: TokenStream) {
for tt in stream {
match tt {
TokenTree::Ident(ident) => entries.push(Entry::Ident(ident)),
TokenTree::Punct(punct) => entries.push(Entry::Punct(punct)),
TokenTree::Literal(literal) => entries.push(Entry::Literal(literal)),
TokenTree::Group(group) => {
let group_start_index = entries.len();
entries.push(Entry::End(0, 0)); // we replace this below
Self::recursive_new(entries, group.stream());
let group_end_index = entries.len();
let group_offset = group_end_index - group_start_index;
entries.push(Entry::End(
-(group_end_index as isize),
-(group_offset as isize),
));
entries[group_start_index] = Entry::Group(group, group_offset);
}
}
}
}
/// Creates a `TokenBuffer` containing all the tokens from the input
/// `proc_macro::TokenStream`.
#[cfg(feature = "proc-macro")]
#[cfg_attr(docsrs, doc(cfg(feature = "proc-macro")))]
pub fn new(stream: proc_macro::TokenStream) -> Self {
Self::new2(stream.into())
}
/// Creates a `TokenBuffer` containing all the tokens from the input
/// `proc_macro2::TokenStream`.
pub fn new2(stream: TokenStream) -> Self {
let mut entries = Vec::new();
Self::recursive_new(&mut entries, stream);
entries.push(Entry::End(-(entries.len() as isize), 0));
Self {
entries: entries.into_boxed_slice(),
}
}
/// Creates a cursor referencing the first token in the buffer and able to
/// traverse until the end of the buffer.
pub fn begin(&self) -> Cursor {
let ptr = self.entries.as_ptr();
unsafe { Cursor::create(ptr, ptr.add(self.entries.len() - 1)) }
}
}
/// A cheaply copyable cursor into a `TokenBuffer`.
///
/// This cursor holds a shared reference into the immutable data which is used
/// internally to represent a `TokenStream`, and can be efficiently manipulated
/// and copied around.
///
/// An empty `Cursor` can be created directly, or one may create a `TokenBuffer`
/// object and get a cursor to its first token with `begin()`.
pub struct Cursor<'a> {
// The current entry which the `Cursor` is pointing at.
ptr: *const Entry,
// This is the only `Entry::End` object which this cursor is allowed to
// point at. All other `End` objects are skipped over in `Cursor::create`.
scope: *const Entry,
// Cursor is covariant in 'a. This field ensures that our pointers are still
// valid.
marker: PhantomData<&'a Entry>,
}
impl<'a> Cursor<'a> {
/// Creates a cursor referencing a static empty TokenStream.
pub fn empty() -> Self {
// It's safe in this situation for us to put an `Entry` object in global
// storage, despite it not actually being safe to send across threads
// (`Ident` is a reference into a thread-local table). This is because
// this entry never includes a `Ident` object.
//
// This wrapper struct allows us to break the rules and put a `Sync`
// object in global storage.
struct UnsafeSyncEntry(Entry);
unsafe impl Sync for UnsafeSyncEntry {}
static EMPTY_ENTRY: UnsafeSyncEntry = UnsafeSyncEntry(Entry::End(0, 0));
Cursor {
ptr: &EMPTY_ENTRY.0,
scope: &EMPTY_ENTRY.0,
marker: PhantomData,
}
}
/// This create method intelligently exits non-explicitly-entered
/// `None`-delimited scopes when the cursor reaches the end of them,
/// allowing for them to be treated transparently.
unsafe fn create(mut ptr: *const Entry, scope: *const Entry) -> Self {
// NOTE: If we're looking at a `End`, we want to advance the cursor
// past it, unless `ptr == scope`, which means that we're at the edge of
// our cursor's scope. We should only have `ptr != scope` at the exit
// from None-delimited groups entered with `ignore_none`.
while let Entry::End(..) = unsafe { &*ptr } {
if ptr::eq(ptr, scope) {
break;
}
ptr = unsafe { ptr.add(1) };
}
Cursor {
ptr,
scope,
marker: PhantomData,
}
}
/// Get the current entry.
fn entry(self) -> &'a Entry {
unsafe { &*self.ptr }
}
/// Bump the cursor to point at the next token after the current one. This
/// is undefined behavior if the cursor is currently looking at an
/// `Entry::End`.
///
/// If the cursor is looking at an `Entry::Group`, the bumped cursor will
/// point at the first token in the group (with the same scope end).
unsafe fn bump_ignore_group(self) -> Cursor<'a> {
unsafe { Cursor::create(self.ptr.offset(1), self.scope) }
}
/// While the cursor is looking at a `None`-delimited group, move it to look
/// at the first token inside instead. If the group is empty, this will move
/// the cursor past the `None`-delimited group.
///
/// WARNING: This mutates its argument.
fn ignore_none(&mut self) {
while let Entry::Group(group, _) = self.entry() {
if group.delimiter() == Delimiter::None {
unsafe { *self = self.bump_ignore_group() };
} else {
break;
}
}
}
/// Checks whether the cursor is currently pointing at the end of its valid
/// scope.
pub fn eof(self) -> bool {
// We're at eof if we're at the end of our scope.
ptr::eq(self.ptr, self.scope)
}
/// If the cursor is pointing at a `Ident`, returns it along with a cursor
/// pointing at the next `TokenTree`.
pub fn ident(mut self) -> Option<(Ident, Cursor<'a>)> {
self.ignore_none();
match self.entry() {
Entry::Ident(ident) => Some((ident.clone(), unsafe { self.bump_ignore_group() })),
_ => None,
}
}
/// If the cursor is pointing at a `Punct`, returns it along with a cursor
/// pointing at the next `TokenTree`.
pub fn punct(mut self) -> Option<(Punct, Cursor<'a>)> {
self.ignore_none();
match self.entry() {
Entry::Punct(punct) if punct.as_char() != '\'' => {
Some((punct.clone(), unsafe { self.bump_ignore_group() }))
}
_ => None,
}
}
/// If the cursor is pointing at a `Literal`, return it along with a cursor
/// pointing at the next `TokenTree`.
pub fn literal(mut self) -> Option<(Literal, Cursor<'a>)> {
self.ignore_none();
match self.entry() {
Entry::Literal(literal) => Some((literal.clone(), unsafe { self.bump_ignore_group() })),
_ => None,
}
}
/// If the cursor is pointing at a `Lifetime`, returns it along with a
/// cursor pointing at the next `TokenTree`.
pub fn lifetime(mut self) -> Option<(Lifetime, Cursor<'a>)> {
self.ignore_none();
match self.entry() {
Entry::Punct(punct) if punct.as_char() == '\'' && punct.spacing() == Spacing::Joint => {
let next = unsafe { self.bump_ignore_group() };
let (ident, rest) = next.ident()?;
let lifetime = Lifetime {
apostrophe: punct.span(),
ident,
};
Some((lifetime, rest))
}
_ => None,
}
}
/// If the cursor is pointing at a `Group` with the given delimiter, returns
/// a cursor into that group and one pointing to the next `TokenTree`.
pub fn group(mut self, delim: Delimiter) -> Option<(Cursor<'a>, DelimSpan, Cursor<'a>)> {
// If we're not trying to enter a none-delimited group, we want to
// ignore them. We have to make sure to _not_ ignore them when we want
// to enter them, of course. For obvious reasons.
if delim != Delimiter::None {
self.ignore_none();
}
if let Entry::Group(group, end_offset) = self.entry() {
if group.delimiter() == delim {
let span = group.delim_span();
let end_of_group = unsafe { self.ptr.add(*end_offset) };
let inside_of_group = unsafe { Cursor::create(self.ptr.add(1), end_of_group) };
let after_group = unsafe { Cursor::create(end_of_group, self.scope) };
return Some((inside_of_group, span, after_group));
}
}
None
}
/// If the cursor is pointing at a `Group`, returns a cursor into the group
/// and one pointing to the next `TokenTree`.
pub fn any_group(self) -> Option<(Cursor<'a>, Delimiter, DelimSpan, Cursor<'a>)> {
if let Entry::Group(group, end_offset) = self.entry() {
let delimiter = group.delimiter();
let span = group.delim_span();
let end_of_group = unsafe { self.ptr.add(*end_offset) };
let inside_of_group = unsafe { Cursor::create(self.ptr.add(1), end_of_group) };
let after_group = unsafe { Cursor::create(end_of_group, self.scope) };
return Some((inside_of_group, delimiter, span, after_group));
}
None
}
pub(crate) fn any_group_token(self) -> Option<(Group, Cursor<'a>)> {
if let Entry::Group(group, end_offset) = self.entry() {
let end_of_group = unsafe { self.ptr.add(*end_offset) };
let after_group = unsafe { Cursor::create(end_of_group, self.scope) };
return Some((group.clone(), after_group));
}
None
}
/// Copies all remaining tokens visible from this cursor into a
/// `TokenStream`.
pub fn token_stream(self) -> TokenStream {
let mut tts = Vec::new();
let mut cursor = self;
while let Some((tt, rest)) = cursor.token_tree() {
tts.push(tt);
cursor = rest;
}
tts.into_iter().collect()
}
/// If the cursor is pointing at a `TokenTree`, returns it along with a
/// cursor pointing at the next `TokenTree`.
///
/// Returns `None` if the cursor has reached the end of its stream.
///
/// This method does not treat `None`-delimited groups as transparent, and
/// will return a `Group(None, ..)` if the cursor is looking at one.
pub fn token_tree(self) -> Option<(TokenTree, Cursor<'a>)> {
let (tree, len) = match self.entry() {
Entry::Group(group, end_offset) => (group.clone().into(), *end_offset),
Entry::Literal(literal) => (literal.clone().into(), 1),
Entry::Ident(ident) => (ident.clone().into(), 1),
Entry::Punct(punct) => (punct.clone().into(), 1),
Entry::End(..) => return None,
};
let rest = unsafe { Cursor::create(self.ptr.add(len), self.scope) };
Some((tree, rest))
}
/// Returns the `Span` of the current token, or `Span::call_site()` if this
/// cursor points to eof.
pub fn span(mut self) -> Span {
match self.entry() {
Entry::Group(group, _) => group.span(),
Entry::Literal(literal) => literal.span(),
Entry::Ident(ident) => ident.span(),
Entry::Punct(punct) => punct.span(),
Entry::End(_, offset) => {
self.ptr = unsafe { self.ptr.offset(*offset) };
if let Entry::Group(group, _) = self.entry() {
group.span_close()
} else {
Span::call_site()
}
}
}
}
/// Returns the `Span` of the token immediately prior to the position of
/// this cursor, or of the current token if there is no previous one.
#[cfg(any(feature = "full", feature = "derive"))]
pub(crate) fn prev_span(mut self) -> Span {
if start_of_buffer(self) < self.ptr {
self.ptr = unsafe { self.ptr.offset(-1) };
}
self.span()
}
/// Skip over the next token that is not a None-delimited group, without
/// cloning it. Returns `None` if this cursor points to eof.
///
/// This method treats `'lifetimes` as a single token.
pub(crate) fn skip(mut self) -> Option<Cursor<'a>> {
self.ignore_none();
let len = match self.entry() {
Entry::End(..) => return None,
// Treat lifetimes as a single tt for the purposes of 'skip'.
Entry::Punct(punct) if punct.as_char() == '\'' && punct.spacing() == Spacing::Joint => {
match unsafe { &*self.ptr.add(1) } {
Entry::Ident(_) => 2,
_ => 1,
}
}
Entry::Group(_, end_offset) => *end_offset,
_ => 1,
};
Some(unsafe { Cursor::create(self.ptr.add(len), self.scope) })
}
pub(crate) fn scope_delimiter(self) -> Delimiter {
match unsafe { &*self.scope } {
Entry::End(_, offset) => match unsafe { &*self.scope.offset(*offset) } {
Entry::Group(group, _) => group.delimiter(),
_ => Delimiter::None,
},
_ => unreachable!(),
}
}
}
impl<'a> Copy for Cursor<'a> {}
impl<'a> Clone for Cursor<'a> {
fn clone(&self) -> Self {
*self
}
}
impl<'a> Eq for Cursor<'a> {}
impl<'a> PartialEq for Cursor<'a> {
fn eq(&self, other: &Self) -> bool {
ptr::eq(self.ptr, other.ptr)
}
}
impl<'a> PartialOrd for Cursor<'a> {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
if same_buffer(*self, *other) {
Some(cmp_assuming_same_buffer(*self, *other))
} else {
None
}
}
}
pub(crate) fn same_scope(a: Cursor, b: Cursor) -> bool {
ptr::eq(a.scope, b.scope)
}
pub(crate) fn same_buffer(a: Cursor, b: Cursor) -> bool {
ptr::eq(start_of_buffer(a), start_of_buffer(b))
}
fn start_of_buffer(cursor: Cursor) -> *const Entry {
unsafe {
match &*cursor.scope {
Entry::End(offset, _) => cursor.scope.offset(*offset),
_ => unreachable!(),
}
}
}
pub(crate) fn cmp_assuming_same_buffer(a: Cursor, b: Cursor) -> Ordering {
a.ptr.cmp(&b.ptr)
}
pub(crate) fn open_span_of_group(cursor: Cursor) -> Span {
match cursor.entry() {
Entry::Group(group, _) => group.span_open(),
_ => cursor.span(),
}
}

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#[cfg(feature = "full")]
use crate::expr::Expr;
#[cfg(any(feature = "printing", feature = "full"))]
use crate::generics::TypeParamBound;
#[cfg(any(feature = "printing", feature = "full"))]
use crate::path::{Path, PathArguments};
#[cfg(any(feature = "printing", feature = "full"))]
use crate::punctuated::Punctuated;
#[cfg(any(feature = "printing", feature = "full"))]
use crate::ty::{ReturnType, Type};
#[cfg(feature = "full")]
use proc_macro2::{Delimiter, TokenStream, TokenTree};
#[cfg(any(feature = "printing", feature = "full"))]
use std::ops::ControlFlow;
#[cfg(feature = "full")]
pub(crate) fn requires_semi_to_be_stmt(expr: &Expr) -> bool {
match expr {
Expr::Macro(expr) => !expr.mac.delimiter.is_brace(),
_ => requires_comma_to_be_match_arm(expr),
}
}
#[cfg(feature = "full")]
pub(crate) fn requires_comma_to_be_match_arm(expr: &Expr) -> bool {
match expr {
Expr::If(_)
| Expr::Match(_)
| Expr::Block(_) | Expr::Unsafe(_) // both under ExprKind::Block in rustc
| Expr::While(_)
| Expr::Loop(_)
| Expr::ForLoop(_)
| Expr::TryBlock(_)
| Expr::Const(_) => false,
Expr::Array(_)
| Expr::Assign(_)
| Expr::Async(_)
| Expr::Await(_)
| Expr::Binary(_)
| Expr::Break(_)
| Expr::Call(_)
| Expr::Cast(_)
| Expr::Closure(_)
| Expr::Continue(_)
| Expr::Field(_)
| Expr::Group(_)
| Expr::Index(_)
| Expr::Infer(_)
| Expr::Let(_)
| Expr::Lit(_)
| Expr::Macro(_)
| Expr::MethodCall(_)
| Expr::Paren(_)
| Expr::Path(_)
| Expr::Range(_)
| Expr::RawAddr(_)
| Expr::Reference(_)
| Expr::Repeat(_)
| Expr::Return(_)
| Expr::Struct(_)
| Expr::Try(_)
| Expr::Tuple(_)
| Expr::Unary(_)
| Expr::Yield(_)
| Expr::Verbatim(_) => true,
}
}
#[cfg(feature = "printing")]
pub(crate) fn trailing_unparameterized_path(mut ty: &Type) -> bool {
loop {
match ty {
Type::BareFn(t) => match &t.output {
ReturnType::Default => return false,
ReturnType::Type(_, ret) => ty = ret,
},
Type::ImplTrait(t) => match last_type_in_bounds(&t.bounds) {
ControlFlow::Break(trailing_path) => return trailing_path,
ControlFlow::Continue(t) => ty = t,
},
Type::Path(t) => match last_type_in_path(&t.path) {
ControlFlow::Break(trailing_path) => return trailing_path,
ControlFlow::Continue(t) => ty = t,
},
Type::Ptr(t) => ty = &t.elem,
Type::Reference(t) => ty = &t.elem,
Type::TraitObject(t) => match last_type_in_bounds(&t.bounds) {
ControlFlow::Break(trailing_path) => return trailing_path,
ControlFlow::Continue(t) => ty = t,
},
Type::Array(_)
| Type::Group(_)
| Type::Infer(_)
| Type::Macro(_)
| Type::Never(_)
| Type::Paren(_)
| Type::Slice(_)
| Type::Tuple(_)
| Type::Verbatim(_) => return false,
}
}
fn last_type_in_path(path: &Path) -> ControlFlow<bool, &Type> {
match &path.segments.last().unwrap().arguments {
PathArguments::None => ControlFlow::Break(true),
PathArguments::AngleBracketed(_) => ControlFlow::Break(false),
PathArguments::Parenthesized(arg) => match &arg.output {
ReturnType::Default => ControlFlow::Break(false),
ReturnType::Type(_, ret) => ControlFlow::Continue(ret),
},
}
}
fn last_type_in_bounds(
bounds: &Punctuated<TypeParamBound, Token![+]>,
) -> ControlFlow<bool, &Type> {
match bounds.last().unwrap() {
TypeParamBound::Trait(t) => last_type_in_path(&t.path),
TypeParamBound::Lifetime(_)
| TypeParamBound::PreciseCapture(_)
| TypeParamBound::Verbatim(_) => ControlFlow::Break(false),
}
}
}
/// Whether the expression's first token is the label of a loop/block.
#[cfg(all(feature = "printing", feature = "full"))]
pub(crate) fn expr_leading_label(mut expr: &Expr) -> bool {
loop {
match expr {
Expr::Block(e) => return e.label.is_some(),
Expr::ForLoop(e) => return e.label.is_some(),
Expr::Loop(e) => return e.label.is_some(),
Expr::While(e) => return e.label.is_some(),
Expr::Assign(e) => expr = &e.left,
Expr::Await(e) => expr = &e.base,
Expr::Binary(e) => expr = &e.left,
Expr::Call(e) => expr = &e.func,
Expr::Cast(e) => expr = &e.expr,
Expr::Field(e) => expr = &e.base,
Expr::Index(e) => expr = &e.expr,
Expr::MethodCall(e) => expr = &e.receiver,
Expr::Range(e) => match &e.start {
Some(start) => expr = start,
None => return false,
},
Expr::Try(e) => expr = &e.expr,
Expr::Array(_)
| Expr::Async(_)
| Expr::Break(_)
| Expr::Closure(_)
| Expr::Const(_)
| Expr::Continue(_)
| Expr::Group(_)
| Expr::If(_)
| Expr::Infer(_)
| Expr::Let(_)
| Expr::Lit(_)
| Expr::Macro(_)
| Expr::Match(_)
| Expr::Paren(_)
| Expr::Path(_)
| Expr::RawAddr(_)
| Expr::Reference(_)
| Expr::Repeat(_)
| Expr::Return(_)
| Expr::Struct(_)
| Expr::TryBlock(_)
| Expr::Tuple(_)
| Expr::Unary(_)
| Expr::Unsafe(_)
| Expr::Verbatim(_)
| Expr::Yield(_) => return false,
}
}
}
/// Whether the expression's last token is `}`.
#[cfg(feature = "full")]
pub(crate) fn expr_trailing_brace(mut expr: &Expr) -> bool {
loop {
match expr {
Expr::Async(_)
| Expr::Block(_)
| Expr::Const(_)
| Expr::ForLoop(_)
| Expr::If(_)
| Expr::Loop(_)
| Expr::Match(_)
| Expr::Struct(_)
| Expr::TryBlock(_)
| Expr::Unsafe(_)
| Expr::While(_) => return true,
Expr::Assign(e) => expr = &e.right,
Expr::Binary(e) => expr = &e.right,
Expr::Break(e) => match &e.expr {
Some(e) => expr = e,
None => return false,
},
Expr::Cast(e) => return type_trailing_brace(&e.ty),
Expr::Closure(e) => expr = &e.body,
Expr::Let(e) => expr = &e.expr,
Expr::Macro(e) => return e.mac.delimiter.is_brace(),
Expr::Range(e) => match &e.end {
Some(end) => expr = end,
None => return false,
},
Expr::RawAddr(e) => expr = &e.expr,
Expr::Reference(e) => expr = &e.expr,
Expr::Return(e) => match &e.expr {
Some(e) => expr = e,
None => return false,
},
Expr::Unary(e) => expr = &e.expr,
Expr::Verbatim(e) => return tokens_trailing_brace(e),
Expr::Yield(e) => match &e.expr {
Some(e) => expr = e,
None => return false,
},
Expr::Array(_)
| Expr::Await(_)
| Expr::Call(_)
| Expr::Continue(_)
| Expr::Field(_)
| Expr::Group(_)
| Expr::Index(_)
| Expr::Infer(_)
| Expr::Lit(_)
| Expr::MethodCall(_)
| Expr::Paren(_)
| Expr::Path(_)
| Expr::Repeat(_)
| Expr::Try(_)
| Expr::Tuple(_) => return false,
}
}
fn type_trailing_brace(mut ty: &Type) -> bool {
loop {
match ty {
Type::BareFn(t) => match &t.output {
ReturnType::Default => return false,
ReturnType::Type(_, ret) => ty = ret,
},
Type::ImplTrait(t) => match last_type_in_bounds(&t.bounds) {
ControlFlow::Break(trailing_brace) => return trailing_brace,
ControlFlow::Continue(t) => ty = t,
},
Type::Macro(t) => return t.mac.delimiter.is_brace(),
Type::Path(t) => match last_type_in_path(&t.path) {
Some(t) => ty = t,
None => return false,
},
Type::Ptr(t) => ty = &t.elem,
Type::Reference(t) => ty = &t.elem,
Type::TraitObject(t) => match last_type_in_bounds(&t.bounds) {
ControlFlow::Break(trailing_brace) => return trailing_brace,
ControlFlow::Continue(t) => ty = t,
},
Type::Verbatim(t) => return tokens_trailing_brace(t),
Type::Array(_)
| Type::Group(_)
| Type::Infer(_)
| Type::Never(_)
| Type::Paren(_)
| Type::Slice(_)
| Type::Tuple(_) => return false,
}
}
}
fn last_type_in_path(path: &Path) -> Option<&Type> {
match &path.segments.last().unwrap().arguments {
PathArguments::None | PathArguments::AngleBracketed(_) => None,
PathArguments::Parenthesized(arg) => match &arg.output {
ReturnType::Default => None,
ReturnType::Type(_, ret) => Some(ret),
},
}
}
fn last_type_in_bounds(
bounds: &Punctuated<TypeParamBound, Token![+]>,
) -> ControlFlow<bool, &Type> {
match bounds.last().unwrap() {
TypeParamBound::Trait(t) => match last_type_in_path(&t.path) {
Some(t) => ControlFlow::Continue(t),
None => ControlFlow::Break(false),
},
TypeParamBound::Lifetime(_) | TypeParamBound::PreciseCapture(_) => {
ControlFlow::Break(false)
}
TypeParamBound::Verbatim(t) => ControlFlow::Break(tokens_trailing_brace(t)),
}
}
fn tokens_trailing_brace(tokens: &TokenStream) -> bool {
if let Some(TokenTree::Group(last)) = tokens.clone().into_iter().last() {
last.delimiter() == Delimiter::Brace
} else {
false
}
}
}

260
rust/syn/custom_keyword.rs Normal file
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/// Define a type that supports parsing and printing a given identifier as if it
/// were a keyword.
///
/// # Usage
///
/// As a convention, it is recommended that this macro be invoked within a
/// module called `kw` or `keyword` and that the resulting parser be invoked
/// with a `kw::` or `keyword::` prefix.
///
/// ```
/// mod kw {
/// syn::custom_keyword!(whatever);
/// }
/// ```
///
/// The generated syntax tree node supports the following operations just like
/// any built-in keyword token.
///
/// - [Peeking] — `input.peek(kw::whatever)`
///
/// - [Parsing] — `input.parse::<kw::whatever>()?`
///
/// - [Printing] — `quote!( ... #whatever_token ... )`
///
/// - Construction from a [`Span`] — `let whatever_token = kw::whatever(sp)`
///
/// - Field access to its span — `let sp = whatever_token.span`
///
/// [Peeking]: crate::parse::ParseBuffer::peek
/// [Parsing]: crate::parse::ParseBuffer::parse
/// [Printing]: quote::ToTokens
/// [`Span`]: proc_macro2::Span
///
/// # Example
///
/// This example parses input that looks like `bool = true` or `str = "value"`.
/// The key must be either the identifier `bool` or the identifier `str`. If
/// `bool`, the value may be either `true` or `false`. If `str`, the value may
/// be any string literal.
///
/// The symbols `bool` and `str` are not reserved keywords in Rust so these are
/// not considered keywords in the `syn::token` module. Like any other
/// identifier that is not a keyword, these can be declared as custom keywords
/// by crates that need to use them as such.
///
/// ```
/// use syn::{LitBool, LitStr, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// mod kw {
/// syn::custom_keyword!(bool);
/// syn::custom_keyword!(str);
/// }
///
/// enum Argument {
/// Bool {
/// bool_token: kw::bool,
/// eq_token: Token![=],
/// value: LitBool,
/// },
/// Str {
/// str_token: kw::str,
/// eq_token: Token![=],
/// value: LitStr,
/// },
/// }
///
/// impl Parse for Argument {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let lookahead = input.lookahead1();
/// if lookahead.peek(kw::bool) {
/// Ok(Argument::Bool {
/// bool_token: input.parse::<kw::bool>()?,
/// eq_token: input.parse()?,
/// value: input.parse()?,
/// })
/// } else if lookahead.peek(kw::str) {
/// Ok(Argument::Str {
/// str_token: input.parse::<kw::str>()?,
/// eq_token: input.parse()?,
/// value: input.parse()?,
/// })
/// } else {
/// Err(lookahead.error())
/// }
/// }
/// }
/// ```
#[macro_export]
macro_rules! custom_keyword {
($ident:ident) => {
#[allow(non_camel_case_types)]
pub struct $ident {
#[allow(dead_code)]
pub span: $crate::__private::Span,
}
#[doc(hidden)]
#[allow(dead_code, non_snake_case)]
pub fn $ident<__S: $crate::__private::IntoSpans<$crate::__private::Span>>(
span: __S,
) -> $ident {
$ident {
span: $crate::__private::IntoSpans::into_spans(span),
}
}
const _: () = {
impl $crate::__private::Default for $ident {
fn default() -> Self {
$ident {
span: $crate::__private::Span::call_site(),
}
}
}
$crate::impl_parse_for_custom_keyword!($ident);
$crate::impl_to_tokens_for_custom_keyword!($ident);
$crate::impl_clone_for_custom_keyword!($ident);
$crate::impl_extra_traits_for_custom_keyword!($ident);
};
};
}
// Not public API.
#[cfg(feature = "parsing")]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_parse_for_custom_keyword {
($ident:ident) => {
// For peek.
impl $crate::__private::CustomToken for $ident {
fn peek(cursor: $crate::buffer::Cursor) -> $crate::__private::bool {
if let $crate::__private::Some((ident, _rest)) = cursor.ident() {
ident == $crate::__private::stringify!($ident)
} else {
false
}
}
fn display() -> &'static $crate::__private::str {
$crate::__private::concat!("`", $crate::__private::stringify!($ident), "`")
}
}
impl $crate::parse::Parse for $ident {
fn parse(input: $crate::parse::ParseStream) -> $crate::parse::Result<$ident> {
input.step(|cursor| {
if let $crate::__private::Some((ident, rest)) = cursor.ident() {
if ident == $crate::__private::stringify!($ident) {
return $crate::__private::Ok(($ident { span: ident.span() }, rest));
}
}
$crate::__private::Err(cursor.error($crate::__private::concat!(
"expected `",
$crate::__private::stringify!($ident),
"`",
)))
})
}
}
};
}
// Not public API.
#[cfg(not(feature = "parsing"))]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_parse_for_custom_keyword {
($ident:ident) => {};
}
// Not public API.
#[cfg(feature = "printing")]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_to_tokens_for_custom_keyword {
($ident:ident) => {
impl $crate::__private::ToTokens for $ident {
fn to_tokens(&self, tokens: &mut $crate::__private::TokenStream2) {
let ident = $crate::Ident::new($crate::__private::stringify!($ident), self.span);
$crate::__private::TokenStreamExt::append(tokens, ident);
}
}
};
}
// Not public API.
#[cfg(not(feature = "printing"))]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_to_tokens_for_custom_keyword {
($ident:ident) => {};
}
// Not public API.
#[cfg(feature = "clone-impls")]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_clone_for_custom_keyword {
($ident:ident) => {
impl $crate::__private::Copy for $ident {}
#[allow(clippy::expl_impl_clone_on_copy)]
impl $crate::__private::Clone for $ident {
fn clone(&self) -> Self {
*self
}
}
};
}
// Not public API.
#[cfg(not(feature = "clone-impls"))]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_clone_for_custom_keyword {
($ident:ident) => {};
}
// Not public API.
#[cfg(feature = "extra-traits")]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_extra_traits_for_custom_keyword {
($ident:ident) => {
impl $crate::__private::Debug for $ident {
fn fmt(&self, f: &mut $crate::__private::Formatter) -> $crate::__private::FmtResult {
$crate::__private::Formatter::write_str(
f,
$crate::__private::concat!(
"Keyword [",
$crate::__private::stringify!($ident),
"]",
),
)
}
}
impl $crate::__private::Eq for $ident {}
impl $crate::__private::PartialEq for $ident {
fn eq(&self, _other: &Self) -> $crate::__private::bool {
true
}
}
impl $crate::__private::Hash for $ident {
fn hash<__H: $crate::__private::Hasher>(&self, _state: &mut __H) {}
}
};
}
// Not public API.
#[cfg(not(feature = "extra-traits"))]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_extra_traits_for_custom_keyword {
($ident:ident) => {};
}

304
rust/syn/custom_punctuation.rs Normal file
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/// Define a type that supports parsing and printing a multi-character symbol
/// as if it were a punctuation token.
///
/// # Usage
///
/// ```
/// syn::custom_punctuation!(LeftRightArrow, <=>);
/// ```
///
/// The generated syntax tree node supports the following operations just like
/// any built-in punctuation token.
///
/// - [Peeking] — `input.peek(LeftRightArrow)`
///
/// - [Parsing] — `input.parse::<LeftRightArrow>()?`
///
/// - [Printing] — `quote!( ... #lrarrow ... )`
///
/// - Construction from a [`Span`] — `let lrarrow = LeftRightArrow(sp)`
///
/// - Construction from multiple [`Span`] — `let lrarrow = LeftRightArrow([sp, sp, sp])`
///
/// - Field access to its spans — `let spans = lrarrow.spans`
///
/// [Peeking]: crate::parse::ParseBuffer::peek
/// [Parsing]: crate::parse::ParseBuffer::parse
/// [Printing]: quote::ToTokens
/// [`Span`]: proc_macro2::Span
///
/// # Example
///
/// ```
/// use proc_macro2::{TokenStream, TokenTree};
/// use syn::parse::{Parse, ParseStream, Peek, Result};
/// use syn::punctuated::Punctuated;
/// use syn::Expr;
///
/// syn::custom_punctuation!(PathSeparator, </>);
///
/// // expr </> expr </> expr ...
/// struct PathSegments {
/// segments: Punctuated<Expr, PathSeparator>,
/// }
///
/// impl Parse for PathSegments {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let mut segments = Punctuated::new();
///
/// let first = parse_until(input, PathSeparator)?;
/// segments.push_value(syn::parse2(first)?);
///
/// while input.peek(PathSeparator) {
/// segments.push_punct(input.parse()?);
///
/// let next = parse_until(input, PathSeparator)?;
/// segments.push_value(syn::parse2(next)?);
/// }
///
/// Ok(PathSegments { segments })
/// }
/// }
///
/// fn parse_until<E: Peek>(input: ParseStream, end: E) -> Result<TokenStream> {
/// let mut tokens = TokenStream::new();
/// while !input.is_empty() && !input.peek(end) {
/// let next: TokenTree = input.parse()?;
/// tokens.extend(Some(next));
/// }
/// Ok(tokens)
/// }
///
/// fn main() {
/// let input = r#" a::b </> c::d::e "#;
/// let _: PathSegments = syn::parse_str(input).unwrap();
/// }
/// ```
#[macro_export]
macro_rules! custom_punctuation {
($ident:ident, $($tt:tt)+) => {
pub struct $ident {
#[allow(dead_code)]
pub spans: $crate::custom_punctuation_repr!($($tt)+),
}
#[doc(hidden)]
#[allow(dead_code, non_snake_case)]
pub fn $ident<__S: $crate::__private::IntoSpans<$crate::custom_punctuation_repr!($($tt)+)>>(
spans: __S,
) -> $ident {
let _validate_len = 0 $(+ $crate::custom_punctuation_len!(strict, $tt))*;
$ident {
spans: $crate::__private::IntoSpans::into_spans(spans)
}
}
const _: () = {
impl $crate::__private::Default for $ident {
fn default() -> Self {
$ident($crate::__private::Span::call_site())
}
}
$crate::impl_parse_for_custom_punctuation!($ident, $($tt)+);
$crate::impl_to_tokens_for_custom_punctuation!($ident, $($tt)+);
$crate::impl_clone_for_custom_punctuation!($ident, $($tt)+);
$crate::impl_extra_traits_for_custom_punctuation!($ident, $($tt)+);
};
};
}
// Not public API.
#[cfg(feature = "parsing")]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_parse_for_custom_punctuation {
($ident:ident, $($tt:tt)+) => {
impl $crate::__private::CustomToken for $ident {
fn peek(cursor: $crate::buffer::Cursor) -> $crate::__private::bool {
$crate::__private::peek_punct(cursor, $crate::stringify_punct!($($tt)+))
}
fn display() -> &'static $crate::__private::str {
$crate::__private::concat!("`", $crate::stringify_punct!($($tt)+), "`")
}
}
impl $crate::parse::Parse for $ident {
fn parse(input: $crate::parse::ParseStream) -> $crate::parse::Result<$ident> {
let spans: $crate::custom_punctuation_repr!($($tt)+) =
$crate::__private::parse_punct(input, $crate::stringify_punct!($($tt)+))?;
Ok($ident(spans))
}
}
};
}
// Not public API.
#[cfg(not(feature = "parsing"))]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_parse_for_custom_punctuation {
($ident:ident, $($tt:tt)+) => {};
}
// Not public API.
#[cfg(feature = "printing")]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_to_tokens_for_custom_punctuation {
($ident:ident, $($tt:tt)+) => {
impl $crate::__private::ToTokens for $ident {
fn to_tokens(&self, tokens: &mut $crate::__private::TokenStream2) {
$crate::__private::print_punct($crate::stringify_punct!($($tt)+), &self.spans, tokens)
}
}
};
}
// Not public API.
#[cfg(not(feature = "printing"))]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_to_tokens_for_custom_punctuation {
($ident:ident, $($tt:tt)+) => {};
}
// Not public API.
#[cfg(feature = "clone-impls")]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_clone_for_custom_punctuation {
($ident:ident, $($tt:tt)+) => {
impl $crate::__private::Copy for $ident {}
#[allow(clippy::expl_impl_clone_on_copy)]
impl $crate::__private::Clone for $ident {
fn clone(&self) -> Self {
*self
}
}
};
}
// Not public API.
#[cfg(not(feature = "clone-impls"))]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_clone_for_custom_punctuation {
($ident:ident, $($tt:tt)+) => {};
}
// Not public API.
#[cfg(feature = "extra-traits")]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_extra_traits_for_custom_punctuation {
($ident:ident, $($tt:tt)+) => {
impl $crate::__private::Debug for $ident {
fn fmt(&self, f: &mut $crate::__private::Formatter) -> $crate::__private::FmtResult {
$crate::__private::Formatter::write_str(f, $crate::__private::stringify!($ident))
}
}
impl $crate::__private::Eq for $ident {}
impl $crate::__private::PartialEq for $ident {
fn eq(&self, _other: &Self) -> $crate::__private::bool {
true
}
}
impl $crate::__private::Hash for $ident {
fn hash<__H: $crate::__private::Hasher>(&self, _state: &mut __H) {}
}
};
}
// Not public API.
#[cfg(not(feature = "extra-traits"))]
#[doc(hidden)]
#[macro_export]
macro_rules! impl_extra_traits_for_custom_punctuation {
($ident:ident, $($tt:tt)+) => {};
}
// Not public API.
#[doc(hidden)]
#[macro_export]
macro_rules! custom_punctuation_repr {
($($tt:tt)+) => {
[$crate::__private::Span; 0 $(+ $crate::custom_punctuation_len!(lenient, $tt))+]
};
}
// Not public API.
#[doc(hidden)]
#[macro_export]
#[rustfmt::skip]
macro_rules! custom_punctuation_len {
($mode:ident, &) => { 1 };
($mode:ident, &&) => { 2 };
($mode:ident, &=) => { 2 };
($mode:ident, @) => { 1 };
($mode:ident, ^) => { 1 };
($mode:ident, ^=) => { 2 };
($mode:ident, :) => { 1 };
($mode:ident, ,) => { 1 };
($mode:ident, $) => { 1 };
($mode:ident, .) => { 1 };
($mode:ident, ..) => { 2 };
($mode:ident, ...) => { 3 };
($mode:ident, ..=) => { 3 };
($mode:ident, =) => { 1 };
($mode:ident, ==) => { 2 };
($mode:ident, =>) => { 2 };
($mode:ident, >=) => { 2 };
($mode:ident, >) => { 1 };
($mode:ident, <-) => { 2 };
($mode:ident, <=) => { 2 };
($mode:ident, <) => { 1 };
($mode:ident, -) => { 1 };
($mode:ident, -=) => { 2 };
($mode:ident, !=) => { 2 };
($mode:ident, !) => { 1 };
($mode:ident, |) => { 1 };
($mode:ident, |=) => { 2 };
($mode:ident, ||) => { 2 };
($mode:ident, ::) => { 2 };
($mode:ident, %) => { 1 };
($mode:ident, %=) => { 2 };
($mode:ident, +) => { 1 };
($mode:ident, +=) => { 2 };
($mode:ident, #) => { 1 };
($mode:ident, ?) => { 1 };
($mode:ident, ->) => { 2 };
($mode:ident, ;) => { 1 };
($mode:ident, <<) => { 2 };
($mode:ident, <<=) => { 3 };
($mode:ident, >>) => { 2 };
($mode:ident, >>=) => { 3 };
($mode:ident, /) => { 1 };
($mode:ident, /=) => { 2 };
($mode:ident, *) => { 1 };
($mode:ident, *=) => { 2 };
($mode:ident, ~) => { 1 };
(lenient, $tt:tt) => { 0 };
(strict, $tt:tt) => {{ $crate::custom_punctuation_unexpected!($tt); 0 }};
}
// Not public API.
#[doc(hidden)]
#[macro_export]
macro_rules! custom_punctuation_unexpected {
() => {};
}
// Not public API.
#[doc(hidden)]
#[macro_export]
macro_rules! stringify_punct {
($($tt:tt)+) => {
$crate::__private::concat!($($crate::__private::stringify!($tt)),+)
};
}

424
rust/syn/data.rs Normal file
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use crate::attr::Attribute;
use crate::expr::{Expr, Index, Member};
use crate::ident::Ident;
use crate::punctuated::{self, Punctuated};
use crate::restriction::{FieldMutability, Visibility};
use crate::token;
use crate::ty::Type;
ast_struct! {
/// An enum variant.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct Variant {
pub attrs: Vec<Attribute>,
/// Name of the variant.
pub ident: Ident,
/// Content stored in the variant.
pub fields: Fields,
/// Explicit discriminant: `Variant = 1`
pub discriminant: Option<(Token![=], Expr)>,
}
}
ast_enum_of_structs! {
/// Data stored within an enum variant or struct.
///
/// # Syntax tree enum
///
/// This type is a [syntax tree enum].
///
/// [syntax tree enum]: crate::expr::Expr#syntax-tree-enums
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub enum Fields {
/// Named fields of a struct or struct variant such as `Point { x: f64,
/// y: f64 }`.
Named(FieldsNamed),
/// Unnamed fields of a tuple struct or tuple variant such as `Some(T)`.
Unnamed(FieldsUnnamed),
/// Unit struct or unit variant such as `None`.
Unit,
}
}
ast_struct! {
/// Named fields of a struct or struct variant such as `Point { x: f64,
/// y: f64 }`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct FieldsNamed {
pub brace_token: token::Brace,
pub named: Punctuated<Field, Token![,]>,
}
}
ast_struct! {
/// Unnamed fields of a tuple struct or tuple variant such as `Some(T)`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct FieldsUnnamed {
pub paren_token: token::Paren,
pub unnamed: Punctuated<Field, Token![,]>,
}
}
impl Fields {
/// Get an iterator over the borrowed [`Field`] items in this object. This
/// iterator can be used to iterate over a named or unnamed struct or
/// variant's fields uniformly.
pub fn iter(&self) -> punctuated::Iter<Field> {
match self {
Fields::Unit => crate::punctuated::empty_punctuated_iter(),
Fields::Named(f) => f.named.iter(),
Fields::Unnamed(f) => f.unnamed.iter(),
}
}
/// Get an iterator over the mutably borrowed [`Field`] items in this
/// object. This iterator can be used to iterate over a named or unnamed
/// struct or variant's fields uniformly.
pub fn iter_mut(&mut self) -> punctuated::IterMut<Field> {
match self {
Fields::Unit => crate::punctuated::empty_punctuated_iter_mut(),
Fields::Named(f) => f.named.iter_mut(),
Fields::Unnamed(f) => f.unnamed.iter_mut(),
}
}
/// Returns the number of fields.
pub fn len(&self) -> usize {
match self {
Fields::Unit => 0,
Fields::Named(f) => f.named.len(),
Fields::Unnamed(f) => f.unnamed.len(),
}
}
/// Returns `true` if there are zero fields.
pub fn is_empty(&self) -> bool {
match self {
Fields::Unit => true,
Fields::Named(f) => f.named.is_empty(),
Fields::Unnamed(f) => f.unnamed.is_empty(),
}
}
return_impl_trait! {
/// Get an iterator over the fields of a struct or variant as [`Member`]s.
/// This iterator can be used to iterate over a named or unnamed struct or
/// variant's fields uniformly.
///
/// # Example
///
/// The following is a simplistic [`Clone`] derive for structs. (A more
/// complete implementation would additionally want to infer trait bounds on
/// the generic type parameters.)
///
/// ```
/// # use quote::quote;
/// #
/// fn derive_clone(input: &syn::ItemStruct) -> proc_macro2::TokenStream {
/// let ident = &input.ident;
/// let members = input.fields.members();
/// let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
/// quote! {
/// impl #impl_generics Clone for #ident #ty_generics #where_clause {
/// fn clone(&self) -> Self {
/// Self {
/// #(#members: self.#members.clone()),*
/// }
/// }
/// }
/// }
/// }
/// ```
///
/// For structs with named fields, it produces an expression like `Self { a:
/// self.a.clone() }`. For structs with unnamed fields, `Self { 0:
/// self.0.clone() }`. And for unit structs, `Self {}`.
pub fn members(&self) -> impl Iterator<Item = Member> + Clone + '_ [Members] {
Members {
fields: self.iter(),
index: 0,
}
}
}
}
impl IntoIterator for Fields {
type Item = Field;
type IntoIter = punctuated::IntoIter<Field>;
fn into_iter(self) -> Self::IntoIter {
match self {
Fields::Unit => Punctuated::<Field, ()>::new().into_iter(),
Fields::Named(f) => f.named.into_iter(),
Fields::Unnamed(f) => f.unnamed.into_iter(),
}
}
}
impl<'a> IntoIterator for &'a Fields {
type Item = &'a Field;
type IntoIter = punctuated::Iter<'a, Field>;
fn into_iter(self) -> Self::IntoIter {
self.iter()
}
}
impl<'a> IntoIterator for &'a mut Fields {
type Item = &'a mut Field;
type IntoIter = punctuated::IterMut<'a, Field>;
fn into_iter(self) -> Self::IntoIter {
self.iter_mut()
}
}
ast_struct! {
/// A field of a struct or enum variant.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct Field {
pub attrs: Vec<Attribute>,
pub vis: Visibility,
pub mutability: FieldMutability,
/// Name of the field, if any.
///
/// Fields of tuple structs have no names.
pub ident: Option<Ident>,
pub colon_token: Option<Token![:]>,
pub ty: Type,
}
}
pub struct Members<'a> {
fields: punctuated::Iter<'a, Field>,
index: u32,
}
impl<'a> Iterator for Members<'a> {
type Item = Member;
fn next(&mut self) -> Option<Self::Item> {
let field = self.fields.next()?;
let member = match &field.ident {
Some(ident) => Member::Named(ident.clone()),
None => {
#[cfg(all(feature = "parsing", feature = "printing"))]
let span = crate::spanned::Spanned::span(&field.ty);
#[cfg(not(all(feature = "parsing", feature = "printing")))]
let span = proc_macro2::Span::call_site();
Member::Unnamed(Index {
index: self.index,
span,
})
}
};
self.index += 1;
Some(member)
}
}
impl<'a> Clone for Members<'a> {
fn clone(&self) -> Self {
Members {
fields: self.fields.clone(),
index: self.index,
}
}
}
#[cfg(feature = "parsing")]
pub(crate) mod parsing {
use crate::attr::Attribute;
use crate::data::{Field, Fields, FieldsNamed, FieldsUnnamed, Variant};
use crate::error::Result;
use crate::expr::Expr;
use crate::ext::IdentExt as _;
use crate::ident::Ident;
#[cfg(not(feature = "full"))]
use crate::parse::discouraged::Speculative as _;
use crate::parse::{Parse, ParseStream};
use crate::restriction::{FieldMutability, Visibility};
#[cfg(not(feature = "full"))]
use crate::scan_expr::scan_expr;
use crate::token;
use crate::ty::Type;
use crate::verbatim;
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for Variant {
fn parse(input: ParseStream) -> Result<Self> {
let attrs = input.call(Attribute::parse_outer)?;
let _visibility: Visibility = input.parse()?;
let ident: Ident = input.parse()?;
let fields = if input.peek(token::Brace) {
Fields::Named(input.parse()?)
} else if input.peek(token::Paren) {
Fields::Unnamed(input.parse()?)
} else {
Fields::Unit
};
let discriminant = if input.peek(Token![=]) {
let eq_token: Token![=] = input.parse()?;
#[cfg(feature = "full")]
let discriminant: Expr = input.parse()?;
#[cfg(not(feature = "full"))]
let discriminant = {
let begin = input.fork();
let ahead = input.fork();
let mut discriminant: Result<Expr> = ahead.parse();
if discriminant.is_ok() {
input.advance_to(&ahead);
} else if scan_expr(input).is_ok() {
discriminant = Ok(Expr::Verbatim(verbatim::between(&begin, input)));
}
discriminant?
};
Some((eq_token, discriminant))
} else {
None
};
Ok(Variant {
attrs,
ident,
fields,
discriminant,
})
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for FieldsNamed {
fn parse(input: ParseStream) -> Result<Self> {
let content;
Ok(FieldsNamed {
brace_token: braced!(content in input),
named: content.parse_terminated(Field::parse_named, Token![,])?,
})
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for FieldsUnnamed {
fn parse(input: ParseStream) -> Result<Self> {
let content;
Ok(FieldsUnnamed {
paren_token: parenthesized!(content in input),
unnamed: content.parse_terminated(Field::parse_unnamed, Token![,])?,
})
}
}
impl Field {
/// Parses a named (braced struct) field.
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_named(input: ParseStream) -> Result<Self> {
let attrs = input.call(Attribute::parse_outer)?;
let vis: Visibility = input.parse()?;
let unnamed_field = cfg!(feature = "full") && input.peek(Token![_]);
let ident = if unnamed_field {
input.call(Ident::parse_any)
} else {
input.parse()
}?;
let colon_token: Token![:] = input.parse()?;
let ty: Type = if unnamed_field
&& (input.peek(Token![struct])
|| input.peek(Token![union]) && input.peek2(token::Brace))
{
let begin = input.fork();
input.call(Ident::parse_any)?;
input.parse::<FieldsNamed>()?;
Type::Verbatim(verbatim::between(&begin, input))
} else {
input.parse()?
};
Ok(Field {
attrs,
vis,
mutability: FieldMutability::None,
ident: Some(ident),
colon_token: Some(colon_token),
ty,
})
}
/// Parses an unnamed (tuple struct) field.
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_unnamed(input: ParseStream) -> Result<Self> {
Ok(Field {
attrs: input.call(Attribute::parse_outer)?,
vis: input.parse()?,
mutability: FieldMutability::None,
ident: None,
colon_token: None,
ty: input.parse()?,
})
}
}
}
#[cfg(feature = "printing")]
mod printing {
use crate::data::{Field, FieldsNamed, FieldsUnnamed, Variant};
use crate::print::TokensOrDefault;
use proc_macro2::TokenStream;
use quote::{ToTokens, TokenStreamExt};
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for Variant {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.append_all(&self.attrs);
self.ident.to_tokens(tokens);
self.fields.to_tokens(tokens);
if let Some((eq_token, disc)) = &self.discriminant {
eq_token.to_tokens(tokens);
disc.to_tokens(tokens);
}
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for FieldsNamed {
fn to_tokens(&self, tokens: &mut TokenStream) {
self.brace_token.surround(tokens, |tokens| {
self.named.to_tokens(tokens);
});
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for FieldsUnnamed {
fn to_tokens(&self, tokens: &mut TokenStream) {
self.paren_token.surround(tokens, |tokens| {
self.unnamed.to_tokens(tokens);
});
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for Field {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.append_all(&self.attrs);
self.vis.to_tokens(tokens);
if let Some(ident) = &self.ident {
ident.to_tokens(tokens);
TokensOrDefault(&self.colon_token).to_tokens(tokens);
}
self.ty.to_tokens(tokens);
}
}
}

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use crate::attr::Attribute;
use crate::data::{Fields, FieldsNamed, Variant};
use crate::generics::Generics;
use crate::ident::Ident;
use crate::punctuated::Punctuated;
use crate::restriction::Visibility;
use crate::token;
ast_struct! {
/// Data structure sent to a `proc_macro_derive` macro.
#[cfg_attr(docsrs, doc(cfg(feature = "derive")))]
pub struct DeriveInput {
pub attrs: Vec<Attribute>,
pub vis: Visibility,
pub ident: Ident,
pub generics: Generics,
pub data: Data,
}
}
ast_enum! {
/// The storage of a struct, enum or union data structure.
///
/// # Syntax tree enum
///
/// This type is a [syntax tree enum].
///
/// [syntax tree enum]: crate::expr::Expr#syntax-tree-enums
#[cfg_attr(docsrs, doc(cfg(feature = "derive")))]
pub enum Data {
Struct(DataStruct),
Enum(DataEnum),
Union(DataUnion),
}
}
ast_struct! {
/// A struct input to a `proc_macro_derive` macro.
#[cfg_attr(docsrs, doc(cfg(feature = "derive")))]
pub struct DataStruct {
pub struct_token: Token![struct],
pub fields: Fields,
pub semi_token: Option<Token![;]>,
}
}
ast_struct! {
/// An enum input to a `proc_macro_derive` macro.
#[cfg_attr(docsrs, doc(cfg(feature = "derive")))]
pub struct DataEnum {
pub enum_token: Token![enum],
pub brace_token: token::Brace,
pub variants: Punctuated<Variant, Token![,]>,
}
}
ast_struct! {
/// An untagged union input to a `proc_macro_derive` macro.
#[cfg_attr(docsrs, doc(cfg(feature = "derive")))]
pub struct DataUnion {
pub union_token: Token![union],
pub fields: FieldsNamed,
}
}
#[cfg(feature = "parsing")]
pub(crate) mod parsing {
use crate::attr::Attribute;
use crate::data::{Fields, FieldsNamed, Variant};
use crate::derive::{Data, DataEnum, DataStruct, DataUnion, DeriveInput};
use crate::error::Result;
use crate::generics::{Generics, WhereClause};
use crate::ident::Ident;
use crate::parse::{Parse, ParseStream};
use crate::punctuated::Punctuated;
use crate::restriction::Visibility;
use crate::token;
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for DeriveInput {
fn parse(input: ParseStream) -> Result<Self> {
let attrs = input.call(Attribute::parse_outer)?;
let vis = input.parse::<Visibility>()?;
let lookahead = input.lookahead1();
if lookahead.peek(Token![struct]) {
let struct_token = input.parse::<Token![struct]>()?;
let ident = input.parse::<Ident>()?;
let generics = input.parse::<Generics>()?;
let (where_clause, fields, semi) = data_struct(input)?;
Ok(DeriveInput {
attrs,
vis,
ident,
generics: Generics {
where_clause,
..generics
},
data: Data::Struct(DataStruct {
struct_token,
fields,
semi_token: semi,
}),
})
} else if lookahead.peek(Token![enum]) {
let enum_token = input.parse::<Token![enum]>()?;
let ident = input.parse::<Ident>()?;
let generics = input.parse::<Generics>()?;
let (where_clause, brace, variants) = data_enum(input)?;
Ok(DeriveInput {
attrs,
vis,
ident,
generics: Generics {
where_clause,
..generics
},
data: Data::Enum(DataEnum {
enum_token,
brace_token: brace,
variants,
}),
})
} else if lookahead.peek(Token![union]) {
let union_token = input.parse::<Token![union]>()?;
let ident = input.parse::<Ident>()?;
let generics = input.parse::<Generics>()?;
let (where_clause, fields) = data_union(input)?;
Ok(DeriveInput {
attrs,
vis,
ident,
generics: Generics {
where_clause,
..generics
},
data: Data::Union(DataUnion {
union_token,
fields,
}),
})
} else {
Err(lookahead.error())
}
}
}
pub(crate) fn data_struct(
input: ParseStream,
) -> Result<(Option<WhereClause>, Fields, Option<Token![;]>)> {
let mut lookahead = input.lookahead1();
let mut where_clause = None;
if lookahead.peek(Token![where]) {
where_clause = Some(input.parse()?);
lookahead = input.lookahead1();
}
if where_clause.is_none() && lookahead.peek(token::Paren) {
let fields = input.parse()?;
lookahead = input.lookahead1();
if lookahead.peek(Token![where]) {
where_clause = Some(input.parse()?);
lookahead = input.lookahead1();
}
if lookahead.peek(Token![;]) {
let semi = input.parse()?;
Ok((where_clause, Fields::Unnamed(fields), Some(semi)))
} else {
Err(lookahead.error())
}
} else if lookahead.peek(token::Brace) {
let fields = input.parse()?;
Ok((where_clause, Fields::Named(fields), None))
} else if lookahead.peek(Token![;]) {
let semi = input.parse()?;
Ok((where_clause, Fields::Unit, Some(semi)))
} else {
Err(lookahead.error())
}
}
pub(crate) fn data_enum(
input: ParseStream,
) -> Result<(
Option<WhereClause>,
token::Brace,
Punctuated<Variant, Token![,]>,
)> {
let where_clause = input.parse()?;
let content;
let brace = braced!(content in input);
let variants = content.parse_terminated(Variant::parse, Token![,])?;
Ok((where_clause, brace, variants))
}
pub(crate) fn data_union(input: ParseStream) -> Result<(Option<WhereClause>, FieldsNamed)> {
let where_clause = input.parse()?;
let fields = input.parse()?;
Ok((where_clause, fields))
}
}
#[cfg(feature = "printing")]
mod printing {
use crate::attr::FilterAttrs;
use crate::data::Fields;
use crate::derive::{Data, DeriveInput};
use crate::print::TokensOrDefault;
use proc_macro2::TokenStream;
use quote::ToTokens;
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for DeriveInput {
fn to_tokens(&self, tokens: &mut TokenStream) {
for attr in self.attrs.outer() {
attr.to_tokens(tokens);
}
self.vis.to_tokens(tokens);
match &self.data {
Data::Struct(d) => d.struct_token.to_tokens(tokens),
Data::Enum(d) => d.enum_token.to_tokens(tokens),
Data::Union(d) => d.union_token.to_tokens(tokens),
}
self.ident.to_tokens(tokens);
self.generics.to_tokens(tokens);
match &self.data {
Data::Struct(data) => match &data.fields {
Fields::Named(fields) => {
self.generics.where_clause.to_tokens(tokens);
fields.to_tokens(tokens);
}
Fields::Unnamed(fields) => {
fields.to_tokens(tokens);
self.generics.where_clause.to_tokens(tokens);
TokensOrDefault(&data.semi_token).to_tokens(tokens);
}
Fields::Unit => {
self.generics.where_clause.to_tokens(tokens);
TokensOrDefault(&data.semi_token).to_tokens(tokens);
}
},
Data::Enum(data) => {
self.generics.where_clause.to_tokens(tokens);
data.brace_token.surround(tokens, |tokens| {
data.variants.to_tokens(tokens);
});
}
Data::Union(data) => {
self.generics.where_clause.to_tokens(tokens);
data.fields.to_tokens(tokens);
}
}
}
}
}

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//! Extensions to the parsing API with niche applicability.
use crate::buffer::Cursor;
use crate::error::Result;
use crate::parse::{inner_unexpected, ParseBuffer, Unexpected};
use proc_macro2::extra::DelimSpan;
use proc_macro2::Delimiter;
use std::cell::Cell;
use std::mem;
use std::rc::Rc;
/// Extensions to the `ParseStream` API to support speculative parsing.
pub trait Speculative {
/// Advance this parse stream to the position of a forked parse stream.
///
/// This is the opposite operation to [`ParseStream::fork`]. You can fork a
/// parse stream, perform some speculative parsing, then join the original
/// stream to the fork to "commit" the parsing from the fork to the main
/// stream.
///
/// If you can avoid doing this, you should, as it limits the ability to
/// generate useful errors. That said, it is often the only way to parse
/// syntax of the form `A* B*` for arbitrary syntax `A` and `B`. The problem
/// is that when the fork fails to parse an `A`, it's impossible to tell
/// whether that was because of a syntax error and the user meant to provide
/// an `A`, or that the `A`s are finished and it's time to start parsing
/// `B`s. Use with care.
///
/// Also note that if `A` is a subset of `B`, `A* B*` can be parsed by
/// parsing `B*` and removing the leading members of `A` from the
/// repetition, bypassing the need to involve the downsides associated with
/// speculative parsing.
///
/// [`ParseStream::fork`]: ParseBuffer::fork
///
/// # Example
///
/// There has been chatter about the possibility of making the colons in the
/// turbofish syntax like `path::to::<T>` no longer required by accepting
/// `path::to<T>` in expression position. Specifically, according to [RFC
/// 2544], [`PathSegment`] parsing should always try to consume a following
/// `<` token as the start of generic arguments, and reset to the `<` if
/// that fails (e.g. the token is acting as a less-than operator).
///
/// This is the exact kind of parsing behavior which requires the "fork,
/// try, commit" behavior that [`ParseStream::fork`] discourages. With
/// `advance_to`, we can avoid having to parse the speculatively parsed
/// content a second time.
///
/// This change in behavior can be implemented in syn by replacing just the
/// `Parse` implementation for `PathSegment`:
///
/// ```
/// # use syn::ext::IdentExt;
/// use syn::parse::discouraged::Speculative;
/// # use syn::parse::{Parse, ParseStream};
/// # use syn::{Ident, PathArguments, Result, Token};
///
/// pub struct PathSegment {
/// pub ident: Ident,
/// pub arguments: PathArguments,
/// }
/// #
/// # impl<T> From<T> for PathSegment
/// # where
/// # T: Into<Ident>,
/// # {
/// # fn from(ident: T) -> Self {
/// # PathSegment {
/// # ident: ident.into(),
/// # arguments: PathArguments::None,
/// # }
/// # }
/// # }
///
/// impl Parse for PathSegment {
/// fn parse(input: ParseStream) -> Result<Self> {
/// if input.peek(Token![super])
/// || input.peek(Token![self])
/// || input.peek(Token![Self])
/// || input.peek(Token![crate])
/// {
/// let ident = input.call(Ident::parse_any)?;
/// return Ok(PathSegment::from(ident));
/// }
///
/// let ident = input.parse()?;
/// if input.peek(Token![::]) && input.peek3(Token![<]) {
/// return Ok(PathSegment {
/// ident,
/// arguments: PathArguments::AngleBracketed(input.parse()?),
/// });
/// }
/// if input.peek(Token![<]) && !input.peek(Token![<=]) {
/// let fork = input.fork();
/// if let Ok(arguments) = fork.parse() {
/// input.advance_to(&fork);
/// return Ok(PathSegment {
/// ident,
/// arguments: PathArguments::AngleBracketed(arguments),
/// });
/// }
/// }
/// Ok(PathSegment::from(ident))
/// }
/// }
///
/// # syn::parse_str::<PathSegment>("a<b,c>").unwrap();
/// ```
///
/// # Drawbacks
///
/// The main drawback of this style of speculative parsing is in error
/// presentation. Even if the lookahead is the "correct" parse, the error
/// that is shown is that of the "fallback" parse. To use the same example
/// as the turbofish above, take the following unfinished "turbofish":
///
/// ```text
/// let _ = f<&'a fn(), for<'a> serde::>();
/// ```
///
/// If this is parsed as generic arguments, we can provide the error message
///
/// ```text
/// error: expected identifier
/// --> src.rs:L:C
/// |
/// L | let _ = f<&'a fn(), for<'a> serde::>();
/// | ^
/// ```
///
/// but if parsed using the above speculative parsing, it falls back to
/// assuming that the `<` is a less-than when it fails to parse the generic
/// arguments, and tries to interpret the `&'a` as the start of a labelled
/// loop, resulting in the much less helpful error
///
/// ```text
/// error: expected `:`
/// --> src.rs:L:C
/// |
/// L | let _ = f<&'a fn(), for<'a> serde::>();
/// | ^^
/// ```
///
/// This can be mitigated with various heuristics (two examples: show both
/// forks' parse errors, or show the one that consumed more tokens), but
/// when you can control the grammar, sticking to something that can be
/// parsed LL(3) and without the LL(*) speculative parsing this makes
/// possible, displaying reasonable errors becomes much more simple.
///
/// [RFC 2544]: https://github.com/rust-lang/rfcs/pull/2544
/// [`PathSegment`]: crate::PathSegment
///
/// # Performance
///
/// This method performs a cheap fixed amount of work that does not depend
/// on how far apart the two streams are positioned.
///
/// # Panics
///
/// The forked stream in the argument of `advance_to` must have been
/// obtained by forking `self`. Attempting to advance to any other stream
/// will cause a panic.
fn advance_to(&self, fork: &Self);
}
impl<'a> Speculative for ParseBuffer<'a> {
fn advance_to(&self, fork: &Self) {
if !crate::buffer::same_scope(self.cursor(), fork.cursor()) {
panic!("fork was not derived from the advancing parse stream");
}
let (self_unexp, self_sp) = inner_unexpected(self);
let (fork_unexp, fork_sp) = inner_unexpected(fork);
if !Rc::ptr_eq(&self_unexp, &fork_unexp) {
match (fork_sp, self_sp) {
// Unexpected set on the fork, but not on `self`, copy it over.
(Some((span, delimiter)), None) => {
self_unexp.set(Unexpected::Some(span, delimiter));
}
// Unexpected unset. Use chain to propagate errors from fork.
(None, None) => {
fork_unexp.set(Unexpected::Chain(self_unexp));
// Ensure toplevel 'unexpected' tokens from the fork don't
// propagate up the chain by replacing the root `unexpected`
// pointer, only 'unexpected' tokens from existing group
// parsers should propagate.
fork.unexpected
.set(Some(Rc::new(Cell::new(Unexpected::None))));
}
// Unexpected has been set on `self`. No changes needed.
(_, Some(_)) => {}
}
}
// See comment on `cell` in the struct definition.
self.cell
.set(unsafe { mem::transmute::<Cursor, Cursor<'static>>(fork.cursor()) });
}
}
/// Extensions to the `ParseStream` API to support manipulating invisible
/// delimiters the same as if they were visible.
pub trait AnyDelimiter {
/// Returns the delimiter, the span of the delimiter token, and the nested
/// contents for further parsing.
fn parse_any_delimiter(&self) -> Result<(Delimiter, DelimSpan, ParseBuffer)>;
}
impl<'a> AnyDelimiter for ParseBuffer<'a> {
fn parse_any_delimiter(&self) -> Result<(Delimiter, DelimSpan, ParseBuffer)> {
self.step(|cursor| {
if let Some((content, delimiter, span, rest)) = cursor.any_group() {
let scope = span.close();
let nested = crate::parse::advance_step_cursor(cursor, content);
let unexpected = crate::parse::get_unexpected(self);
let content = crate::parse::new_parse_buffer(scope, nested, unexpected);
Ok(((delimiter, span, content), rest))
} else {
Err(cursor.error("expected any delimiter"))
}
})
}
}

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use std::iter;
use std::mem::ManuallyDrop;
use std::ops::{Deref, DerefMut};
use std::option;
use std::slice;
#[repr(transparent)]
pub(crate) struct NoDrop<T: ?Sized>(ManuallyDrop<T>);
impl<T> NoDrop<T> {
pub(crate) fn new(value: T) -> Self
where
T: TrivialDrop,
{
NoDrop(ManuallyDrop::new(value))
}
}
impl<T: ?Sized> Deref for NoDrop<T> {
type Target = T;
fn deref(&self) -> &Self::Target {
&self.0
}
}
impl<T: ?Sized> DerefMut for NoDrop<T> {
fn deref_mut(&mut self) -> &mut Self::Target {
&mut self.0
}
}
pub(crate) trait TrivialDrop {}
impl<T> TrivialDrop for iter::Empty<T> {}
impl<T> TrivialDrop for slice::Iter<'_, T> {}
impl<T> TrivialDrop for slice::IterMut<'_, T> {}
impl<T> TrivialDrop for option::IntoIter<&T> {}
impl<T> TrivialDrop for option::IntoIter<&mut T> {}
#[test]
fn test_needs_drop() {
use std::mem::needs_drop;
struct NeedsDrop;
impl Drop for NeedsDrop {
fn drop(&mut self) {}
}
assert!(needs_drop::<NeedsDrop>());
// Test each of the types with a handwritten TrivialDrop impl above.
assert!(!needs_drop::<iter::Empty<NeedsDrop>>());
assert!(!needs_drop::<slice::Iter<NeedsDrop>>());
assert!(!needs_drop::<slice::IterMut<NeedsDrop>>());
assert!(!needs_drop::<option::IntoIter<&NeedsDrop>>());
assert!(!needs_drop::<option::IntoIter<&mut NeedsDrop>>());
}

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#[cfg(feature = "parsing")]
use crate::buffer::Cursor;
use crate::thread::ThreadBound;
use proc_macro2::{
Delimiter, Group, Ident, LexError, Literal, Punct, Spacing, Span, TokenStream, TokenTree,
};
#[cfg(feature = "printing")]
use quote::ToTokens;
use std::fmt::{self, Debug, Display};
use std::slice;
use std::vec;
/// The result of a Syn parser.
pub type Result<T> = std::result::Result<T, Error>;
/// Error returned when a Syn parser cannot parse the input tokens.
///
/// # Error reporting in proc macros
///
/// The correct way to report errors back to the compiler from a procedural
/// macro is by emitting an appropriately spanned invocation of
/// [`compile_error!`] in the generated code. This produces a better diagnostic
/// message than simply panicking the macro.
///
/// [`compile_error!`]: std::compile_error!
///
/// When parsing macro input, the [`parse_macro_input!`] macro handles the
/// conversion to `compile_error!` automatically.
///
/// [`parse_macro_input!`]: crate::parse_macro_input!
///
/// ```
/// # extern crate proc_macro;
/// #
/// use proc_macro::TokenStream;
/// use syn::parse::{Parse, ParseStream, Result};
/// use syn::{parse_macro_input, ItemFn};
///
/// # const IGNORE: &str = stringify! {
/// #[proc_macro_attribute]
/// # };
/// pub fn my_attr(args: TokenStream, input: TokenStream) -> TokenStream {
/// let args = parse_macro_input!(args as MyAttrArgs);
/// let input = parse_macro_input!(input as ItemFn);
///
/// /* ... */
/// # TokenStream::new()
/// }
///
/// struct MyAttrArgs {
/// # _k: [(); { stringify! {
/// ...
/// # }; 0 }]
/// }
///
/// impl Parse for MyAttrArgs {
/// fn parse(input: ParseStream) -> Result<Self> {
/// # stringify! {
/// ...
/// # };
/// # unimplemented!()
/// }
/// }
/// ```
///
/// For errors that arise later than the initial parsing stage, the
/// [`.to_compile_error()`] or [`.into_compile_error()`] methods can be used to
/// perform an explicit conversion to `compile_error!`.
///
/// [`.to_compile_error()`]: Error::to_compile_error
/// [`.into_compile_error()`]: Error::into_compile_error
///
/// ```
/// # extern crate proc_macro;
/// #
/// # use proc_macro::TokenStream;
/// # use syn::{parse_macro_input, DeriveInput};
/// #
/// # const IGNORE: &str = stringify! {
/// #[proc_macro_derive(MyDerive)]
/// # };
/// pub fn my_derive(input: TokenStream) -> TokenStream {
/// let input = parse_macro_input!(input as DeriveInput);
///
/// // fn(DeriveInput) -> syn::Result<proc_macro2::TokenStream>
/// expand::my_derive(input)
/// .unwrap_or_else(syn::Error::into_compile_error)
/// .into()
/// }
/// #
/// # mod expand {
/// # use proc_macro2::TokenStream;
/// # use syn::{DeriveInput, Result};
/// #
/// # pub fn my_derive(input: DeriveInput) -> Result<TokenStream> {
/// # unimplemented!()
/// # }
/// # }
/// ```
pub struct Error {
messages: Vec<ErrorMessage>,
}
struct ErrorMessage {
// Span is implemented as an index into a thread-local interner to keep the
// size small. It is not safe to access from a different thread. We want
// errors to be Send and Sync to play nicely with ecosystem crates for error
// handling, so pin the span we're given to its original thread and assume
// it is Span::call_site if accessed from any other thread.
span: ThreadBound<SpanRange>,
message: String,
}
// Cannot use std::ops::Range<Span> because that does not implement Copy,
// whereas ThreadBound<T> requires a Copy impl as a way to ensure no Drop impls
// are involved.
struct SpanRange {
start: Span,
end: Span,
}
#[cfg(test)]
struct _Test
where
Error: Send + Sync;
impl Error {
/// Usually the [`ParseStream::error`] method will be used instead, which
/// automatically uses the correct span from the current position of the
/// parse stream.
///
/// Use `Error::new` when the error needs to be triggered on some span other
/// than where the parse stream is currently positioned.
///
/// [`ParseStream::error`]: crate::parse::ParseBuffer::error
///
/// # Example
///
/// ```
/// use syn::{Error, Ident, LitStr, Result, Token};
/// use syn::parse::ParseStream;
///
/// // Parses input that looks like `name = "string"` where the key must be
/// // the identifier `name` and the value may be any string literal.
/// // Returns the string literal.
/// fn parse_name(input: ParseStream) -> Result<LitStr> {
/// let name_token: Ident = input.parse()?;
/// if name_token != "name" {
/// // Trigger an error not on the current position of the stream,
/// // but on the position of the unexpected identifier.
/// return Err(Error::new(name_token.span(), "expected `name`"));
/// }
/// input.parse::<Token![=]>()?;
/// let s: LitStr = input.parse()?;
/// Ok(s)
/// }
/// ```
pub fn new<T: Display>(span: Span, message: T) -> Self {
return new(span, message.to_string());
fn new(span: Span, message: String) -> Error {
Error {
messages: vec![ErrorMessage {
span: ThreadBound::new(SpanRange {
start: span,
end: span,
}),
message,
}],
}
}
}
/// Creates an error with the specified message spanning the given syntax
/// tree node.
///
/// Unlike the `Error::new` constructor, this constructor takes an argument
/// `tokens` which is a syntax tree node. This allows the resulting `Error`
/// to attempt to span all tokens inside of `tokens`. While you would
/// typically be able to use the `Spanned` trait with the above `Error::new`
/// constructor, implementation limitations today mean that
/// `Error::new_spanned` may provide a higher-quality error message on
/// stable Rust.
///
/// When in doubt it's recommended to stick to `Error::new` (or
/// `ParseStream::error`)!
#[cfg(feature = "printing")]
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
pub fn new_spanned<T: ToTokens, U: Display>(tokens: T, message: U) -> Self {
return new_spanned(tokens.into_token_stream(), message.to_string());
fn new_spanned(tokens: TokenStream, message: String) -> Error {
let mut iter = tokens.into_iter();
let start = iter.next().map_or_else(Span::call_site, |t| t.span());
let end = iter.last().map_or(start, |t| t.span());
Error {
messages: vec![ErrorMessage {
span: ThreadBound::new(SpanRange { start, end }),
message,
}],
}
}
}
/// The source location of the error.
///
/// Spans are not thread-safe so this function returns `Span::call_site()`
/// if called from a different thread than the one on which the `Error` was
/// originally created.
pub fn span(&self) -> Span {
let SpanRange { start, end } = match self.messages[0].span.get() {
Some(span) => *span,
None => return Span::call_site(),
};
start.join(end).unwrap_or(start)
}
/// Render the error as an invocation of [`compile_error!`].
///
/// The [`parse_macro_input!`] macro provides a convenient way to invoke
/// this method correctly in a procedural macro.
///
/// [`compile_error!`]: std::compile_error!
/// [`parse_macro_input!`]: crate::parse_macro_input!
pub fn to_compile_error(&self) -> TokenStream {
self.messages
.iter()
.map(ErrorMessage::to_compile_error)
.collect()
}
/// Render the error as an invocation of [`compile_error!`].
///
/// [`compile_error!`]: std::compile_error!
///
/// # Example
///
/// ```
/// # extern crate proc_macro;
/// #
/// use proc_macro::TokenStream;
/// use syn::{parse_macro_input, DeriveInput, Error};
///
/// # const _: &str = stringify! {
/// #[proc_macro_derive(MyTrait)]
/// # };
/// pub fn derive_my_trait(input: TokenStream) -> TokenStream {
/// let input = parse_macro_input!(input as DeriveInput);
/// my_trait::expand(input)
/// .unwrap_or_else(Error::into_compile_error)
/// .into()
/// }
///
/// mod my_trait {
/// use proc_macro2::TokenStream;
/// use syn::{DeriveInput, Result};
///
/// pub(crate) fn expand(input: DeriveInput) -> Result<TokenStream> {
/// /* ... */
/// # unimplemented!()
/// }
/// }
/// ```
pub fn into_compile_error(self) -> TokenStream {
self.to_compile_error()
}
/// Add another error message to self such that when `to_compile_error()` is
/// called, both errors will be emitted together.
pub fn combine(&mut self, another: Error) {
self.messages.extend(another.messages);
}
}
impl ErrorMessage {
fn to_compile_error(&self) -> TokenStream {
let (start, end) = match self.span.get() {
Some(range) => (range.start, range.end),
None => (Span::call_site(), Span::call_site()),
};
// ::core::compile_error!($message)
TokenStream::from_iter([
TokenTree::Punct({
let mut punct = Punct::new(':', Spacing::Joint);
punct.set_span(start);
punct
}),
TokenTree::Punct({
let mut punct = Punct::new(':', Spacing::Alone);
punct.set_span(start);
punct
}),
TokenTree::Ident(Ident::new("core", start)),
TokenTree::Punct({
let mut punct = Punct::new(':', Spacing::Joint);
punct.set_span(start);
punct
}),
TokenTree::Punct({
let mut punct = Punct::new(':', Spacing::Alone);
punct.set_span(start);
punct
}),
TokenTree::Ident(Ident::new("compile_error", start)),
TokenTree::Punct({
let mut punct = Punct::new('!', Spacing::Alone);
punct.set_span(start);
punct
}),
TokenTree::Group({
let mut group = Group::new(Delimiter::Brace, {
TokenStream::from_iter([TokenTree::Literal({
let mut string = Literal::string(&self.message);
string.set_span(end);
string
})])
});
group.set_span(end);
group
}),
])
}
}
#[cfg(feature = "parsing")]
pub(crate) fn new_at<T: Display>(scope: Span, cursor: Cursor, message: T) -> Error {
if cursor.eof() {
Error::new(scope, format!("unexpected end of input, {}", message))
} else {
let span = crate::buffer::open_span_of_group(cursor);
Error::new(span, message)
}
}
#[cfg(all(feature = "parsing", any(feature = "full", feature = "derive")))]
pub(crate) fn new2<T: Display>(start: Span, end: Span, message: T) -> Error {
return new2(start, end, message.to_string());
fn new2(start: Span, end: Span, message: String) -> Error {
Error {
messages: vec![ErrorMessage {
span: ThreadBound::new(SpanRange { start, end }),
message,
}],
}
}
}
impl Debug for Error {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
if self.messages.len() == 1 {
formatter
.debug_tuple("Error")
.field(&self.messages[0])
.finish()
} else {
formatter
.debug_tuple("Error")
.field(&self.messages)
.finish()
}
}
}
impl Debug for ErrorMessage {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
Debug::fmt(&self.message, formatter)
}
}
impl Display for Error {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
formatter.write_str(&self.messages[0].message)
}
}
impl Clone for Error {
fn clone(&self) -> Self {
Error {
messages: self.messages.clone(),
}
}
}
impl Clone for ErrorMessage {
fn clone(&self) -> Self {
ErrorMessage {
span: self.span,
message: self.message.clone(),
}
}
}
impl Clone for SpanRange {
fn clone(&self) -> Self {
*self
}
}
impl Copy for SpanRange {}
impl std::error::Error for Error {}
impl From<LexError> for Error {
fn from(err: LexError) -> Self {
Error::new(err.span(), err)
}
}
impl IntoIterator for Error {
type Item = Error;
type IntoIter = IntoIter;
fn into_iter(self) -> Self::IntoIter {
IntoIter {
messages: self.messages.into_iter(),
}
}
}
pub struct IntoIter {
messages: vec::IntoIter<ErrorMessage>,
}
impl Iterator for IntoIter {
type Item = Error;
fn next(&mut self) -> Option<Self::Item> {
Some(Error {
messages: vec![self.messages.next()?],
})
}
}
impl<'a> IntoIterator for &'a Error {
type Item = Error;
type IntoIter = Iter<'a>;
fn into_iter(self) -> Self::IntoIter {
Iter {
messages: self.messages.iter(),
}
}
}
pub struct Iter<'a> {
messages: slice::Iter<'a, ErrorMessage>,
}
impl<'a> Iterator for Iter<'a> {
type Item = Error;
fn next(&mut self) -> Option<Self::Item> {
Some(Error {
messages: vec![self.messages.next()?.clone()],
})
}
}
impl Extend<Error> for Error {
fn extend<T: IntoIterator<Item = Error>>(&mut self, iter: T) {
for err in iter {
self.combine(err);
}
}
}

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#[doc(hidden)]
pub use std::clone::Clone;
#[doc(hidden)]
pub use std::cmp::{Eq, PartialEq};
#[doc(hidden)]
pub use std::concat;
#[doc(hidden)]
pub use std::default::Default;
#[doc(hidden)]
pub use std::fmt::Debug;
#[doc(hidden)]
pub use std::hash::{Hash, Hasher};
#[doc(hidden)]
pub use std::marker::Copy;
#[doc(hidden)]
pub use std::option::Option::{None, Some};
#[doc(hidden)]
pub use std::result::Result::{Err, Ok};
#[doc(hidden)]
pub use std::stringify;
#[doc(hidden)]
pub type Formatter<'a> = std::fmt::Formatter<'a>;
#[doc(hidden)]
pub type FmtResult = std::fmt::Result;
#[doc(hidden)]
pub type bool = std::primitive::bool;
#[doc(hidden)]
pub type str = std::primitive::str;
#[cfg(feature = "printing")]
#[doc(hidden)]
pub use quote;
#[doc(hidden)]
pub type Span = proc_macro2::Span;
#[doc(hidden)]
pub type TokenStream2 = proc_macro2::TokenStream;
#[cfg(feature = "parsing")]
#[doc(hidden)]
pub use crate::group::{parse_braces, parse_brackets, parse_parens};
#[doc(hidden)]
pub use crate::span::IntoSpans;
#[cfg(all(feature = "parsing", feature = "printing"))]
#[doc(hidden)]
pub use crate::parse_quote::parse as parse_quote;
#[cfg(feature = "parsing")]
#[doc(hidden)]
pub use crate::token::parsing::{peek_punct, punct as parse_punct};
#[cfg(feature = "printing")]
#[doc(hidden)]
pub use crate::token::printing::punct as print_punct;
#[cfg(feature = "parsing")]
#[doc(hidden)]
pub use crate::token::private::CustomToken;
#[cfg(feature = "proc-macro")]
#[doc(hidden)]
pub type TokenStream = proc_macro::TokenStream;
#[cfg(feature = "printing")]
#[doc(hidden)]
pub use quote::{ToTokens, TokenStreamExt};
#[doc(hidden)]
pub struct private(pub(crate) ());

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//! Extension traits to provide parsing methods on foreign types.
use crate::buffer::Cursor;
use crate::error::Result;
use crate::parse::ParseStream;
use crate::parse::Peek;
use crate::sealed::lookahead;
use crate::token::CustomToken;
use proc_macro2::Ident;
/// Additional methods for `Ident` not provided by proc-macro2 or libproc_macro.
///
/// This trait is sealed and cannot be implemented for types outside of Syn. It
/// is implemented only for `proc_macro2::Ident`.
pub trait IdentExt: Sized + private::Sealed {
/// Parses any identifier including keywords.
///
/// This is useful when parsing macro input which allows Rust keywords as
/// identifiers.
///
/// # Example
///
/// ```
/// use syn::{Error, Ident, Result, Token};
/// use syn::ext::IdentExt;
/// use syn::parse::ParseStream;
///
/// mod kw {
/// syn::custom_keyword!(name);
/// }
///
/// // Parses input that looks like `name = NAME` where `NAME` can be
/// // any identifier.
/// //
/// // Examples:
/// //
/// // name = anything
/// // name = impl
/// fn parse_dsl(input: ParseStream) -> Result<Ident> {
/// input.parse::<kw::name>()?;
/// input.parse::<Token![=]>()?;
/// let name = input.call(Ident::parse_any)?;
/// Ok(name)
/// }
/// ```
fn parse_any(input: ParseStream) -> Result<Self>;
/// Peeks any identifier including keywords. Usage:
/// `input.peek(Ident::peek_any)`
///
/// This is different from `input.peek(Ident)` which only returns true in
/// the case of an ident which is not a Rust keyword.
#[allow(non_upper_case_globals)]
const peek_any: private::PeekFn = private::PeekFn;
/// Strips the raw marker `r#`, if any, from the beginning of an ident.
///
/// - unraw(`x`) = `x`
/// - unraw(`move`) = `move`
/// - unraw(`r#move`) = `move`
///
/// # Example
///
/// In the case of interop with other languages like Python that have a
/// different set of keywords than Rust, we might come across macro input
/// that involves raw identifiers to refer to ordinary variables in the
/// other language with a name that happens to be a Rust keyword.
///
/// The function below appends an identifier from the caller's input onto a
/// fixed prefix. Without using `unraw()`, this would tend to produce
/// invalid identifiers like `__pyo3_get_r#move`.
///
/// ```
/// use proc_macro2::Span;
/// use syn::Ident;
/// use syn::ext::IdentExt;
///
/// fn ident_for_getter(variable: &Ident) -> Ident {
/// let getter = format!("__pyo3_get_{}", variable.unraw());
/// Ident::new(&getter, Span::call_site())
/// }
/// ```
fn unraw(&self) -> Ident;
}
impl IdentExt for Ident {
fn parse_any(input: ParseStream) -> Result<Self> {
input.step(|cursor| match cursor.ident() {
Some((ident, rest)) => Ok((ident, rest)),
None => Err(cursor.error("expected ident")),
})
}
fn unraw(&self) -> Ident {
let string = self.to_string();
if let Some(string) = string.strip_prefix("r#") {
Ident::new(string, self.span())
} else {
self.clone()
}
}
}
impl Peek for private::PeekFn {
type Token = private::IdentAny;
}
impl CustomToken for private::IdentAny {
fn peek(cursor: Cursor) -> bool {
cursor.ident().is_some()
}
fn display() -> &'static str {
"identifier"
}
}
impl lookahead::Sealed for private::PeekFn {}
mod private {
use proc_macro2::Ident;
pub trait Sealed {}
impl Sealed for Ident {}
pub struct PeekFn;
pub struct IdentAny;
impl Copy for PeekFn {}
impl Clone for PeekFn {
fn clone(&self) -> Self {
*self
}
}
}

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use crate::attr::Attribute;
use crate::item::Item;
ast_struct! {
/// A complete file of Rust source code.
///
/// Typically `File` objects are created with [`parse_file`].
///
/// [`parse_file`]: crate::parse_file
///
/// # Example
///
/// Parse a Rust source file into a `syn::File` and print out a debug
/// representation of the syntax tree.
///
/// ```
/// use std::env;
/// use std::fs;
/// use std::process;
///
/// fn main() {
/// # }
/// #
/// # fn fake_main() {
/// let mut args = env::args();
/// let _ = args.next(); // executable name
///
/// let filename = match (args.next(), args.next()) {
/// (Some(filename), None) => filename,
/// _ => {
/// eprintln!("Usage: dump-syntax path/to/filename.rs");
/// process::exit(1);
/// }
/// };
///
/// let src = fs::read_to_string(&filename).expect("unable to read file");
/// let syntax = syn::parse_file(&src).expect("unable to parse file");
///
/// // Debug impl is available if Syn is built with "extra-traits" feature.
/// println!("{:#?}", syntax);
/// }
/// ```
///
/// Running with its own source code as input, this program prints output
/// that begins with:
///
/// ```text
/// File {
/// shebang: None,
/// attrs: [],
/// items: [
/// Use(
/// ItemUse {
/// attrs: [],
/// vis: Inherited,
/// use_token: Use,
/// leading_colon: None,
/// tree: Path(
/// UsePath {
/// ident: Ident(
/// std,
/// ),
/// colon2_token: Colon2,
/// tree: Name(
/// UseName {
/// ident: Ident(
/// env,
/// ),
/// },
/// ),
/// },
/// ),
/// semi_token: Semi,
/// },
/// ),
/// ...
/// ```
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct File {
pub shebang: Option<String>,
pub attrs: Vec<Attribute>,
pub items: Vec<Item>,
}
}
#[cfg(feature = "parsing")]
pub(crate) mod parsing {
use crate::attr::Attribute;
use crate::error::Result;
use crate::file::File;
use crate::parse::{Parse, ParseStream};
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for File {
fn parse(input: ParseStream) -> Result<Self> {
Ok(File {
shebang: None,
attrs: input.call(Attribute::parse_inner)?,
items: {
let mut items = Vec::new();
while !input.is_empty() {
items.push(input.parse()?);
}
items
},
})
}
}
}
#[cfg(feature = "printing")]
mod printing {
use crate::attr::FilterAttrs;
use crate::file::File;
use proc_macro2::TokenStream;
use quote::{ToTokens, TokenStreamExt};
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for File {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.append_all(self.attrs.inner());
tokens.append_all(&self.items);
}
}
}

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use crate::classify;
use crate::expr::Expr;
#[cfg(feature = "full")]
use crate::expr::{
ExprBreak, ExprRange, ExprRawAddr, ExprReference, ExprReturn, ExprUnary, ExprYield,
};
use crate::precedence::Precedence;
#[cfg(feature = "full")]
use crate::ty::ReturnType;
pub(crate) struct FixupContext {
#[cfg(feature = "full")]
previous_operator: Precedence,
#[cfg(feature = "full")]
next_operator: Precedence,
// Print expression such that it can be parsed back as a statement
// consisting of the original expression.
//
// The effect of this is for binary operators in statement position to set
// `leftmost_subexpression_in_stmt` when printing their left-hand operand.
//
// (match x {}) - 1; // match needs parens when LHS of binary operator
//
// match x {}; // not when its own statement
//
#[cfg(feature = "full")]
stmt: bool,
// This is the difference between:
//
// (match x {}) - 1; // subexpression needs parens
//
// let _ = match x {} - 1; // no parens
//
// There are 3 distinguishable contexts in which `print_expr` might be
// called with the expression `$match` as its argument, where `$match`
// represents an expression of kind `ExprKind::Match`:
//
// - stmt=false leftmost_subexpression_in_stmt=false
//
// Example: `let _ = $match - 1;`
//
// No parentheses required.
//
// - stmt=false leftmost_subexpression_in_stmt=true
//
// Example: `$match - 1;`
//
// Must parenthesize `($match)`, otherwise parsing back the output as a
// statement would terminate the statement after the closing brace of
// the match, parsing `-1;` as a separate statement.
//
// - stmt=true leftmost_subexpression_in_stmt=false
//
// Example: `$match;`
//
// No parentheses required.
#[cfg(feature = "full")]
leftmost_subexpression_in_stmt: bool,
// Print expression such that it can be parsed as a match arm.
//
// This is almost equivalent to `stmt`, but the grammar diverges a tiny bit
// between statements and match arms when it comes to braced macro calls.
// Macro calls with brace delimiter terminate a statement without a
// semicolon, but do not terminate a match-arm without comma.
//
// m! {} - 1; // two statements: a macro call followed by -1 literal
//
// match () {
// _ => m! {} - 1, // binary subtraction operator
// }
//
#[cfg(feature = "full")]
match_arm: bool,
// This is almost equivalent to `leftmost_subexpression_in_stmt`, other than
// for braced macro calls.
//
// If we have `m! {} - 1` as an expression, the leftmost subexpression
// `m! {}` will need to be parenthesized in the statement case but not the
// match-arm case.
//
// (m! {}) - 1; // subexpression needs parens
//
// match () {
// _ => m! {} - 1, // no parens
// }
//
#[cfg(feature = "full")]
leftmost_subexpression_in_match_arm: bool,
// This is the difference between:
//
// if let _ = (Struct {}) {} // needs parens
//
// match () {
// () if let _ = Struct {} => {} // no parens
// }
//
#[cfg(feature = "full")]
condition: bool,
// This is the difference between:
//
// if break Struct {} == (break) {} // needs parens
//
// if break break == Struct {} {} // no parens
//
#[cfg(feature = "full")]
rightmost_subexpression_in_condition: bool,
// This is the difference between:
//
// if break ({ x }).field + 1 {} needs parens
//
// if break 1 + { x }.field {} // no parens
//
#[cfg(feature = "full")]
leftmost_subexpression_in_optional_operand: bool,
// This is the difference between:
//
// let _ = (return) - 1; // without paren, this would return -1
//
// let _ = return + 1; // no paren because '+' cannot begin expr
//
#[cfg(feature = "full")]
next_operator_can_begin_expr: bool,
// This is the difference between:
//
// let _ = 1 + return 1; // no parens if rightmost subexpression
//
// let _ = 1 + (return 1) + 1; // needs parens
//
#[cfg(feature = "full")]
next_operator_can_continue_expr: bool,
// This is the difference between:
//
// let _ = x as u8 + T;
//
// let _ = (x as u8) < T;
//
// Without parens, the latter would want to parse `u8<T...` as a type.
next_operator_can_begin_generics: bool,
}
impl FixupContext {
/// The default amount of fixing is minimal fixing. Fixups should be turned
/// on in a targeted fashion where needed.
pub const NONE: Self = FixupContext {
#[cfg(feature = "full")]
previous_operator: Precedence::MIN,
#[cfg(feature = "full")]
next_operator: Precedence::MIN,
#[cfg(feature = "full")]
stmt: false,
#[cfg(feature = "full")]
leftmost_subexpression_in_stmt: false,
#[cfg(feature = "full")]
match_arm: false,
#[cfg(feature = "full")]
leftmost_subexpression_in_match_arm: false,
#[cfg(feature = "full")]
condition: false,
#[cfg(feature = "full")]
rightmost_subexpression_in_condition: false,
#[cfg(feature = "full")]
leftmost_subexpression_in_optional_operand: false,
#[cfg(feature = "full")]
next_operator_can_begin_expr: false,
#[cfg(feature = "full")]
next_operator_can_continue_expr: false,
next_operator_can_begin_generics: false,
};
/// Create the initial fixup for printing an expression in statement
/// position.
#[cfg(feature = "full")]
pub fn new_stmt() -> Self {
FixupContext {
stmt: true,
..FixupContext::NONE
}
}
/// Create the initial fixup for printing an expression as the right-hand
/// side of a match arm.
#[cfg(feature = "full")]
pub fn new_match_arm() -> Self {
FixupContext {
match_arm: true,
..FixupContext::NONE
}
}
/// Create the initial fixup for printing an expression as the "condition"
/// of an `if` or `while`. There are a few other positions which are
/// grammatically equivalent and also use this, such as the iterator
/// expression in `for` and the scrutinee in `match`.
#[cfg(feature = "full")]
pub fn new_condition() -> Self {
FixupContext {
condition: true,
rightmost_subexpression_in_condition: true,
..FixupContext::NONE
}
}
/// Transform this fixup into the one that should apply when printing the
/// leftmost subexpression of the current expression.
///
/// The leftmost subexpression is any subexpression that has the same first
/// token as the current expression, but has a different last token.
///
/// For example in `$a + $b` and `$a.method()`, the subexpression `$a` is a
/// leftmost subexpression.
///
/// Not every expression has a leftmost subexpression. For example neither
/// `-$a` nor `[$a]` have one.
pub fn leftmost_subexpression_with_operator(
self,
expr: &Expr,
#[cfg(feature = "full")] next_operator_can_begin_expr: bool,
next_operator_can_begin_generics: bool,
#[cfg(feature = "full")] precedence: Precedence,
) -> (Precedence, Self) {
let fixup = FixupContext {
#[cfg(feature = "full")]
next_operator: precedence,
#[cfg(feature = "full")]
stmt: false,
#[cfg(feature = "full")]
leftmost_subexpression_in_stmt: self.stmt || self.leftmost_subexpression_in_stmt,
#[cfg(feature = "full")]
match_arm: false,
#[cfg(feature = "full")]
leftmost_subexpression_in_match_arm: self.match_arm
|| self.leftmost_subexpression_in_match_arm,
#[cfg(feature = "full")]
rightmost_subexpression_in_condition: false,
#[cfg(feature = "full")]
next_operator_can_begin_expr,
#[cfg(feature = "full")]
next_operator_can_continue_expr: true,
next_operator_can_begin_generics,
..self
};
(fixup.leftmost_subexpression_precedence(expr), fixup)
}
/// Transform this fixup into the one that should apply when printing a
/// leftmost subexpression followed by a `.` or `?` token, which confer
/// different statement boundary rules compared to other leftmost
/// subexpressions.
pub fn leftmost_subexpression_with_dot(self, expr: &Expr) -> (Precedence, Self) {
let fixup = FixupContext {
#[cfg(feature = "full")]
next_operator: Precedence::Unambiguous,
#[cfg(feature = "full")]
stmt: self.stmt || self.leftmost_subexpression_in_stmt,
#[cfg(feature = "full")]
leftmost_subexpression_in_stmt: false,
#[cfg(feature = "full")]
match_arm: self.match_arm || self.leftmost_subexpression_in_match_arm,
#[cfg(feature = "full")]
leftmost_subexpression_in_match_arm: false,
#[cfg(feature = "full")]
rightmost_subexpression_in_condition: false,
#[cfg(feature = "full")]
next_operator_can_begin_expr: false,
#[cfg(feature = "full")]
next_operator_can_continue_expr: true,
next_operator_can_begin_generics: false,
..self
};
(fixup.leftmost_subexpression_precedence(expr), fixup)
}
fn leftmost_subexpression_precedence(self, expr: &Expr) -> Precedence {
#[cfg(feature = "full")]
if !self.next_operator_can_begin_expr || self.next_operator == Precedence::Range {
if let Scan::Bailout = scan_right(expr, self, Precedence::MIN, 0, 0) {
if scan_left(expr, self) {
return Precedence::Unambiguous;
}
}
}
self.precedence(expr)
}
/// Transform this fixup into the one that should apply when printing the
/// rightmost subexpression of the current expression.
///
/// The rightmost subexpression is any subexpression that has a different
/// first token than the current expression, but has the same last token.
///
/// For example in `$a + $b` and `-$b`, the subexpression `$b` is a
/// rightmost subexpression.
///
/// Not every expression has a rightmost subexpression. For example neither
/// `[$b]` nor `$a.f($b)` have one.
pub fn rightmost_subexpression(
self,
expr: &Expr,
#[cfg(feature = "full")] precedence: Precedence,
) -> (Precedence, Self) {
let fixup = self.rightmost_subexpression_fixup(
#[cfg(feature = "full")]
false,
#[cfg(feature = "full")]
false,
#[cfg(feature = "full")]
precedence,
);
(fixup.rightmost_subexpression_precedence(expr), fixup)
}
pub fn rightmost_subexpression_fixup(
self,
#[cfg(feature = "full")] reset_allow_struct: bool,
#[cfg(feature = "full")] optional_operand: bool,
#[cfg(feature = "full")] precedence: Precedence,
) -> Self {
FixupContext {
#[cfg(feature = "full")]
previous_operator: precedence,
#[cfg(feature = "full")]
stmt: false,
#[cfg(feature = "full")]
leftmost_subexpression_in_stmt: false,
#[cfg(feature = "full")]
match_arm: false,
#[cfg(feature = "full")]
leftmost_subexpression_in_match_arm: false,
#[cfg(feature = "full")]
condition: self.condition && !reset_allow_struct,
#[cfg(feature = "full")]
leftmost_subexpression_in_optional_operand: self.condition && optional_operand,
..self
}
}
pub fn rightmost_subexpression_precedence(self, expr: &Expr) -> Precedence {
let default_prec = self.precedence(expr);
#[cfg(feature = "full")]
if match self.previous_operator {
Precedence::Assign | Precedence::Let | Precedence::Prefix => {
default_prec < self.previous_operator
}
_ => default_prec <= self.previous_operator,
} && match self.next_operator {
Precedence::Range | Precedence::Or | Precedence::And => true,
_ => !self.next_operator_can_begin_expr,
} {
if let Scan::Bailout | Scan::Fail = scan_right(expr, self, self.previous_operator, 1, 0)
{
if scan_left(expr, self) {
return Precedence::Prefix;
}
}
}
default_prec
}
/// Determine whether parentheses are needed around the given expression to
/// head off the early termination of a statement or condition.
#[cfg(feature = "full")]
pub fn parenthesize(self, expr: &Expr) -> bool {
(self.leftmost_subexpression_in_stmt && !classify::requires_semi_to_be_stmt(expr))
|| ((self.stmt || self.leftmost_subexpression_in_stmt) && matches!(expr, Expr::Let(_)))
|| (self.leftmost_subexpression_in_match_arm
&& !classify::requires_comma_to_be_match_arm(expr))
|| (self.condition && matches!(expr, Expr::Struct(_)))
|| (self.rightmost_subexpression_in_condition
&& matches!(
expr,
Expr::Return(ExprReturn { expr: None, .. })
| Expr::Yield(ExprYield { expr: None, .. })
))
|| (self.rightmost_subexpression_in_condition
&& !self.condition
&& matches!(
expr,
Expr::Break(ExprBreak { expr: None, .. })
| Expr::Path(_)
| Expr::Range(ExprRange { end: None, .. })
))
|| (self.leftmost_subexpression_in_optional_operand
&& matches!(expr, Expr::Block(expr) if expr.attrs.is_empty() && expr.label.is_none()))
}
/// Determines the effective precedence of a subexpression. Some expressions
/// have higher or lower precedence when adjacent to particular operators.
fn precedence(self, expr: &Expr) -> Precedence {
#[cfg(feature = "full")]
if self.next_operator_can_begin_expr {
// Decrease precedence of value-less jumps when followed by an
// operator that would otherwise get interpreted as beginning a
// value for the jump.
if let Expr::Break(ExprBreak { expr: None, .. })
| Expr::Return(ExprReturn { expr: None, .. })
| Expr::Yield(ExprYield { expr: None, .. }) = expr
{
return Precedence::Jump;
}
}
#[cfg(feature = "full")]
if !self.next_operator_can_continue_expr {
match expr {
// Increase precedence of expressions that extend to the end of
// current statement or group.
Expr::Break(_)
| Expr::Closure(_)
| Expr::Let(_)
| Expr::Return(_)
| Expr::Yield(_) => {
return Precedence::Prefix;
}
Expr::Range(e) if e.start.is_none() => return Precedence::Prefix,
_ => {}
}
}
if self.next_operator_can_begin_generics {
if let Expr::Cast(cast) = expr {
if classify::trailing_unparameterized_path(&cast.ty) {
return Precedence::MIN;
}
}
}
Precedence::of(expr)
}
}
impl Copy for FixupContext {}
impl Clone for FixupContext {
fn clone(&self) -> Self {
*self
}
}
#[cfg(feature = "full")]
enum Scan {
Fail,
Bailout,
Consume,
}
#[cfg(feature = "full")]
impl Copy for Scan {}
#[cfg(feature = "full")]
impl Clone for Scan {
fn clone(&self) -> Self {
*self
}
}
#[cfg(feature = "full")]
impl PartialEq for Scan {
fn eq(&self, other: &Self) -> bool {
*self as u8 == *other as u8
}
}
#[cfg(feature = "full")]
fn scan_left(expr: &Expr, fixup: FixupContext) -> bool {
match expr {
Expr::Assign(_) => fixup.previous_operator <= Precedence::Assign,
Expr::Binary(e) => match Precedence::of_binop(&e.op) {
Precedence::Assign => fixup.previous_operator <= Precedence::Assign,
binop_prec => fixup.previous_operator < binop_prec,
},
Expr::Cast(_) => fixup.previous_operator < Precedence::Cast,
Expr::Range(e) => e.start.is_none() || fixup.previous_operator < Precedence::Assign,
_ => true,
}
}
#[cfg(feature = "full")]
fn scan_right(
expr: &Expr,
fixup: FixupContext,
precedence: Precedence,
fail_offset: u8,
bailout_offset: u8,
) -> Scan {
let consume_by_precedence = if match precedence {
Precedence::Assign | Precedence::Compare => precedence <= fixup.next_operator,
_ => precedence < fixup.next_operator,
} || fixup.next_operator == Precedence::MIN
{
Scan::Consume
} else {
Scan::Bailout
};
if fixup.parenthesize(expr) {
return consume_by_precedence;
}
match expr {
Expr::Assign(e) if e.attrs.is_empty() => {
if match fixup.next_operator {
Precedence::Unambiguous => fail_offset >= 2,
_ => bailout_offset >= 1,
} {
return Scan::Consume;
}
let right_fixup = fixup.rightmost_subexpression_fixup(false, false, Precedence::Assign);
let scan = scan_right(
&e.right,
right_fixup,
Precedence::Assign,
match fixup.next_operator {
Precedence::Unambiguous => fail_offset,
_ => 1,
},
1,
);
if let Scan::Bailout | Scan::Consume = scan {
Scan::Consume
} else if let Precedence::Unambiguous = fixup.next_operator {
Scan::Fail
} else {
Scan::Bailout
}
}
Expr::Binary(e) if e.attrs.is_empty() => {
if match fixup.next_operator {
Precedence::Unambiguous => {
fail_offset >= 2
&& (consume_by_precedence == Scan::Consume || bailout_offset >= 1)
}
_ => bailout_offset >= 1,
} {
return Scan::Consume;
}
let binop_prec = Precedence::of_binop(&e.op);
if binop_prec == Precedence::Compare && fixup.next_operator == Precedence::Compare {
return Scan::Consume;
}
let right_fixup = fixup.rightmost_subexpression_fixup(false, false, binop_prec);
let scan = scan_right(
&e.right,
right_fixup,
binop_prec,
match fixup.next_operator {
Precedence::Unambiguous => fail_offset,
_ => 1,
},
consume_by_precedence as u8 - Scan::Bailout as u8,
);
match scan {
Scan::Fail => {}
Scan::Bailout => return consume_by_precedence,
Scan::Consume => return Scan::Consume,
}
let right_needs_group = binop_prec != Precedence::Assign
&& right_fixup.rightmost_subexpression_precedence(&e.right) <= binop_prec;
if right_needs_group {
consume_by_precedence
} else if let (Scan::Fail, Precedence::Unambiguous) = (scan, fixup.next_operator) {
Scan::Fail
} else {
Scan::Bailout
}
}
Expr::RawAddr(ExprRawAddr { expr, .. })
| Expr::Reference(ExprReference { expr, .. })
| Expr::Unary(ExprUnary { expr, .. }) => {
if match fixup.next_operator {
Precedence::Unambiguous => {
fail_offset >= 2
&& (consume_by_precedence == Scan::Consume || bailout_offset >= 1)
}
_ => bailout_offset >= 1,
} {
return Scan::Consume;
}
let right_fixup = fixup.rightmost_subexpression_fixup(false, false, Precedence::Prefix);
let scan = scan_right(
expr,
right_fixup,
precedence,
match fixup.next_operator {
Precedence::Unambiguous => fail_offset,
_ => 1,
},
consume_by_precedence as u8 - Scan::Bailout as u8,
);
match scan {
Scan::Fail => {}
Scan::Bailout => return consume_by_precedence,
Scan::Consume => return Scan::Consume,
}
if right_fixup.rightmost_subexpression_precedence(expr) < Precedence::Prefix {
consume_by_precedence
} else if let (Scan::Fail, Precedence::Unambiguous) = (scan, fixup.next_operator) {
Scan::Fail
} else {
Scan::Bailout
}
}
Expr::Range(e) if e.attrs.is_empty() => match &e.end {
Some(end) => {
if fail_offset >= 2 {
return Scan::Consume;
}
let right_fixup =
fixup.rightmost_subexpression_fixup(false, true, Precedence::Range);
let scan = scan_right(
end,
right_fixup,
Precedence::Range,
fail_offset,
match fixup.next_operator {
Precedence::Assign | Precedence::Range => 0,
_ => 1,
},
);
if match (scan, fixup.next_operator) {
(Scan::Fail, _) => false,
(Scan::Bailout, Precedence::Assign | Precedence::Range) => false,
(Scan::Bailout | Scan::Consume, _) => true,
} {
return Scan::Consume;
}
if right_fixup.rightmost_subexpression_precedence(end) <= Precedence::Range {
Scan::Consume
} else {
Scan::Fail
}
}
None => {
if fixup.next_operator_can_begin_expr {
Scan::Consume
} else {
Scan::Fail
}
}
},
Expr::Break(e) => match &e.expr {
Some(value) => {
if bailout_offset >= 1 || e.label.is_none() && classify::expr_leading_label(value) {
return Scan::Consume;
}
let right_fixup = fixup.rightmost_subexpression_fixup(true, true, Precedence::Jump);
match scan_right(value, right_fixup, Precedence::Jump, 1, 1) {
Scan::Fail => Scan::Bailout,
Scan::Bailout | Scan::Consume => Scan::Consume,
}
}
None => match fixup.next_operator {
Precedence::Assign if precedence > Precedence::Assign => Scan::Fail,
_ => Scan::Consume,
},
},
Expr::Return(ExprReturn { expr, .. }) | Expr::Yield(ExprYield { expr, .. }) => match expr {
Some(e) => {
if bailout_offset >= 1 {
return Scan::Consume;
}
let right_fixup =
fixup.rightmost_subexpression_fixup(true, false, Precedence::Jump);
match scan_right(e, right_fixup, Precedence::Jump, 1, 1) {
Scan::Fail => Scan::Bailout,
Scan::Bailout | Scan::Consume => Scan::Consume,
}
}
None => match fixup.next_operator {
Precedence::Assign if precedence > Precedence::Assign => Scan::Fail,
_ => Scan::Consume,
},
},
Expr::Closure(e) => {
if matches!(e.output, ReturnType::Default)
|| matches!(&*e.body, Expr::Block(body) if body.attrs.is_empty() && body.label.is_none())
{
if bailout_offset >= 1 {
return Scan::Consume;
}
let right_fixup =
fixup.rightmost_subexpression_fixup(false, false, Precedence::Jump);
match scan_right(&e.body, right_fixup, Precedence::Jump, 1, 1) {
Scan::Fail => Scan::Bailout,
Scan::Bailout | Scan::Consume => Scan::Consume,
}
} else {
Scan::Consume
}
}
Expr::Let(e) => {
if bailout_offset >= 1 {
return Scan::Consume;
}
let right_fixup = fixup.rightmost_subexpression_fixup(false, false, Precedence::Let);
let scan = scan_right(
&e.expr,
right_fixup,
Precedence::Let,
1,
if fixup.next_operator < Precedence::Let {
0
} else {
1
},
);
match scan {
Scan::Fail | Scan::Bailout if fixup.next_operator < Precedence::Let => {
return Scan::Bailout;
}
Scan::Consume => return Scan::Consume,
_ => {}
}
if right_fixup.rightmost_subexpression_precedence(&e.expr) < Precedence::Let {
Scan::Consume
} else if let Scan::Fail = scan {
Scan::Bailout
} else {
Scan::Consume
}
}
Expr::Array(_)
| Expr::Assign(_)
| Expr::Async(_)
| Expr::Await(_)
| Expr::Binary(_)
| Expr::Block(_)
| Expr::Call(_)
| Expr::Cast(_)
| Expr::Const(_)
| Expr::Continue(_)
| Expr::Field(_)
| Expr::ForLoop(_)
| Expr::Group(_)
| Expr::If(_)
| Expr::Index(_)
| Expr::Infer(_)
| Expr::Lit(_)
| Expr::Loop(_)
| Expr::Macro(_)
| Expr::Match(_)
| Expr::MethodCall(_)
| Expr::Paren(_)
| Expr::Path(_)
| Expr::Range(_)
| Expr::Repeat(_)
| Expr::Struct(_)
| Expr::Try(_)
| Expr::TryBlock(_)
| Expr::Tuple(_)
| Expr::Unsafe(_)
| Expr::Verbatim(_)
| Expr::While(_) => match fixup.next_operator {
Precedence::Assign | Precedence::Range if precedence == Precedence::Range => Scan::Fail,
_ if precedence == Precedence::Let && fixup.next_operator < Precedence::Let => {
Scan::Fail
}
_ => consume_by_precedence,
},
}
}

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@@ -0,0 +1,291 @@
use crate::error::Result;
use crate::parse::ParseBuffer;
use crate::token;
use proc_macro2::extra::DelimSpan;
use proc_macro2::Delimiter;
// Not public API.
#[doc(hidden)]
pub struct Parens<'a> {
#[doc(hidden)]
pub token: token::Paren,
#[doc(hidden)]
pub content: ParseBuffer<'a>,
}
// Not public API.
#[doc(hidden)]
pub struct Braces<'a> {
#[doc(hidden)]
pub token: token::Brace,
#[doc(hidden)]
pub content: ParseBuffer<'a>,
}
// Not public API.
#[doc(hidden)]
pub struct Brackets<'a> {
#[doc(hidden)]
pub token: token::Bracket,
#[doc(hidden)]
pub content: ParseBuffer<'a>,
}
// Not public API.
#[cfg(any(feature = "full", feature = "derive"))]
#[doc(hidden)]
pub struct Group<'a> {
#[doc(hidden)]
pub token: token::Group,
#[doc(hidden)]
pub content: ParseBuffer<'a>,
}
// Not public API.
#[doc(hidden)]
pub fn parse_parens<'a>(input: &ParseBuffer<'a>) -> Result<Parens<'a>> {
parse_delimited(input, Delimiter::Parenthesis).map(|(span, content)| Parens {
token: token::Paren(span),
content,
})
}
// Not public API.
#[doc(hidden)]
pub fn parse_braces<'a>(input: &ParseBuffer<'a>) -> Result<Braces<'a>> {
parse_delimited(input, Delimiter::Brace).map(|(span, content)| Braces {
token: token::Brace(span),
content,
})
}
// Not public API.
#[doc(hidden)]
pub fn parse_brackets<'a>(input: &ParseBuffer<'a>) -> Result<Brackets<'a>> {
parse_delimited(input, Delimiter::Bracket).map(|(span, content)| Brackets {
token: token::Bracket(span),
content,
})
}
#[cfg(any(feature = "full", feature = "derive"))]
pub(crate) fn parse_group<'a>(input: &ParseBuffer<'a>) -> Result<Group<'a>> {
parse_delimited(input, Delimiter::None).map(|(span, content)| Group {
token: token::Group(span.join()),
content,
})
}
fn parse_delimited<'a>(
input: &ParseBuffer<'a>,
delimiter: Delimiter,
) -> Result<(DelimSpan, ParseBuffer<'a>)> {
input.step(|cursor| {
if let Some((content, span, rest)) = cursor.group(delimiter) {
let scope = span.close();
let nested = crate::parse::advance_step_cursor(cursor, content);
let unexpected = crate::parse::get_unexpected(input);
let content = crate::parse::new_parse_buffer(scope, nested, unexpected);
Ok(((span, content), rest))
} else {
let message = match delimiter {
Delimiter::Parenthesis => "expected parentheses",
Delimiter::Brace => "expected curly braces",
Delimiter::Bracket => "expected square brackets",
Delimiter::None => "expected invisible group",
};
Err(cursor.error(message))
}
})
}
/// Parse a set of parentheses and expose their content to subsequent parsers.
///
/// # Example
///
/// ```
/// # use quote::quote;
/// #
/// use syn::{parenthesized, token, Ident, Result, Token, Type};
/// use syn::parse::{Parse, ParseStream};
/// use syn::punctuated::Punctuated;
///
/// // Parse a simplified tuple struct syntax like:
/// //
/// // struct S(A, B);
/// struct TupleStruct {
/// struct_token: Token![struct],
/// ident: Ident,
/// paren_token: token::Paren,
/// fields: Punctuated<Type, Token![,]>,
/// semi_token: Token![;],
/// }
///
/// impl Parse for TupleStruct {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let content;
/// Ok(TupleStruct {
/// struct_token: input.parse()?,
/// ident: input.parse()?,
/// paren_token: parenthesized!(content in input),
/// fields: content.parse_terminated(Type::parse, Token![,])?,
/// semi_token: input.parse()?,
/// })
/// }
/// }
/// #
/// # fn main() {
/// # let input = quote! {
/// # struct S(A, B);
/// # };
/// # syn::parse2::<TupleStruct>(input).unwrap();
/// # }
/// ```
#[macro_export]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
macro_rules! parenthesized {
($content:ident in $cursor:expr) => {
match $crate::__private::parse_parens(&$cursor) {
$crate::__private::Ok(parens) => {
$content = parens.content;
parens.token
}
$crate::__private::Err(error) => {
return $crate::__private::Err(error);
}
}
};
}
/// Parse a set of curly braces and expose their content to subsequent parsers.
///
/// # Example
///
/// ```
/// # use quote::quote;
/// #
/// use syn::{braced, token, Ident, Result, Token, Type};
/// use syn::parse::{Parse, ParseStream};
/// use syn::punctuated::Punctuated;
///
/// // Parse a simplified struct syntax like:
/// //
/// // struct S {
/// // a: A,
/// // b: B,
/// // }
/// struct Struct {
/// struct_token: Token![struct],
/// ident: Ident,
/// brace_token: token::Brace,
/// fields: Punctuated<Field, Token![,]>,
/// }
///
/// struct Field {
/// name: Ident,
/// colon_token: Token![:],
/// ty: Type,
/// }
///
/// impl Parse for Struct {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let content;
/// Ok(Struct {
/// struct_token: input.parse()?,
/// ident: input.parse()?,
/// brace_token: braced!(content in input),
/// fields: content.parse_terminated(Field::parse, Token![,])?,
/// })
/// }
/// }
///
/// impl Parse for Field {
/// fn parse(input: ParseStream) -> Result<Self> {
/// Ok(Field {
/// name: input.parse()?,
/// colon_token: input.parse()?,
/// ty: input.parse()?,
/// })
/// }
/// }
/// #
/// # fn main() {
/// # let input = quote! {
/// # struct S {
/// # a: A,
/// # b: B,
/// # }
/// # };
/// # syn::parse2::<Struct>(input).unwrap();
/// # }
/// ```
#[macro_export]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
macro_rules! braced {
($content:ident in $cursor:expr) => {
match $crate::__private::parse_braces(&$cursor) {
$crate::__private::Ok(braces) => {
$content = braces.content;
braces.token
}
$crate::__private::Err(error) => {
return $crate::__private::Err(error);
}
}
};
}
/// Parse a set of square brackets and expose their content to subsequent
/// parsers.
///
/// # Example
///
/// ```
/// # use quote::quote;
/// #
/// use proc_macro2::TokenStream;
/// use syn::{bracketed, token, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Parse an outer attribute like:
/// //
/// // #[repr(C, packed)]
/// struct OuterAttribute {
/// pound_token: Token![#],
/// bracket_token: token::Bracket,
/// content: TokenStream,
/// }
///
/// impl Parse for OuterAttribute {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let content;
/// Ok(OuterAttribute {
/// pound_token: input.parse()?,
/// bracket_token: bracketed!(content in input),
/// content: content.parse()?,
/// })
/// }
/// }
/// #
/// # fn main() {
/// # let input = quote! {
/// # #[repr(C, packed)]
/// # };
/// # syn::parse2::<OuterAttribute>(input).unwrap();
/// # }
/// ```
#[macro_export]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
macro_rules! bracketed {
($content:ident in $cursor:expr) => {
match $crate::__private::parse_brackets(&$cursor) {
$crate::__private::Ok(brackets) => {
$content = brackets.content;
brackets.token
}
$crate::__private::Err(error) => {
return $crate::__private::Err(error);
}
}
};
}

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#[cfg(feature = "parsing")]
use crate::lookahead;
pub use proc_macro2::Ident;
#[cfg(feature = "parsing")]
pub_if_not_doc! {
#[doc(hidden)]
#[allow(non_snake_case)]
pub fn Ident(marker: lookahead::TokenMarker) -> Ident {
match marker {}
}
}
macro_rules! ident_from_token {
($token:ident) => {
impl From<Token![$token]> for Ident {
fn from(token: Token![$token]) -> Ident {
Ident::new(stringify!($token), token.span)
}
}
};
}
ident_from_token!(self);
ident_from_token!(Self);
ident_from_token!(super);
ident_from_token!(crate);
ident_from_token!(extern);
impl From<Token![_]> for Ident {
fn from(token: Token![_]) -> Ident {
Ident::new("_", token.span)
}
}
pub(crate) fn xid_ok(symbol: &str) -> bool {
let mut chars = symbol.chars();
let first = chars.next().unwrap();
if !(first == '_' || unicode_ident::is_xid_start(first)) {
return false;
}
for ch in chars {
if !unicode_ident::is_xid_continue(ch) {
return false;
}
}
true
}
#[cfg(feature = "parsing")]
mod parsing {
use crate::buffer::Cursor;
use crate::error::Result;
use crate::parse::{Parse, ParseStream};
use crate::token::Token;
use proc_macro2::Ident;
fn accept_as_ident(ident: &Ident) -> bool {
match ident.to_string().as_str() {
"_" |
// Based on https://doc.rust-lang.org/1.65.0/reference/keywords.html
"abstract" | "as" | "async" | "await" | "become" | "box" | "break" |
"const" | "continue" | "crate" | "do" | "dyn" | "else" | "enum" |
"extern" | "false" | "final" | "fn" | "for" | "if" | "impl" | "in" |
"let" | "loop" | "macro" | "match" | "mod" | "move" | "mut" |
"override" | "priv" | "pub" | "ref" | "return" | "Self" | "self" |
"static" | "struct" | "super" | "trait" | "true" | "try" | "type" |
"typeof" | "unsafe" | "unsized" | "use" | "virtual" | "where" |
"while" | "yield" => false,
_ => true,
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for Ident {
fn parse(input: ParseStream) -> Result<Self> {
input.step(|cursor| {
if let Some((ident, rest)) = cursor.ident() {
if accept_as_ident(&ident) {
Ok((ident, rest))
} else {
Err(cursor.error(format_args!(
"expected identifier, found keyword `{}`",
ident,
)))
}
} else {
Err(cursor.error("expected identifier"))
}
})
}
}
impl Token for Ident {
fn peek(cursor: Cursor) -> bool {
if let Some((ident, _rest)) = cursor.ident() {
accept_as_ident(&ident)
} else {
false
}
}
fn display() -> &'static str {
"identifier"
}
}
}

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#[cfg(feature = "parsing")]
use crate::lookahead;
use proc_macro2::{Ident, Span};
use std::cmp::Ordering;
use std::fmt::{self, Display};
use std::hash::{Hash, Hasher};
/// A Rust lifetime: `'a`.
///
/// Lifetime names must conform to the following rules:
///
/// - Must start with an apostrophe.
/// - Must not consist of just an apostrophe: `'`.
/// - Character after the apostrophe must be `_` or a Unicode code point with
/// the XID_Start property.
/// - All following characters must be Unicode code points with the XID_Continue
/// property.
pub struct Lifetime {
pub apostrophe: Span,
pub ident: Ident,
}
impl Lifetime {
/// # Panics
///
/// Panics if the lifetime does not conform to the bulleted rules above.
///
/// # Invocation
///
/// ```
/// # use proc_macro2::Span;
/// # use syn::Lifetime;
/// #
/// # fn f() -> Lifetime {
/// Lifetime::new("'a", Span::call_site())
/// # }
/// ```
pub fn new(symbol: &str, span: Span) -> Self {
if !symbol.starts_with('\'') {
panic!(
"lifetime name must start with apostrophe as in \"'a\", got {:?}",
symbol
);
}
if symbol == "'" {
panic!("lifetime name must not be empty");
}
if !crate::ident::xid_ok(&symbol[1..]) {
panic!("{:?} is not a valid lifetime name", symbol);
}
Lifetime {
apostrophe: span,
ident: Ident::new(&symbol[1..], span),
}
}
pub fn span(&self) -> Span {
self.apostrophe
.join(self.ident.span())
.unwrap_or(self.apostrophe)
}
pub fn set_span(&mut self, span: Span) {
self.apostrophe = span;
self.ident.set_span(span);
}
}
impl Display for Lifetime {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
"'".fmt(formatter)?;
self.ident.fmt(formatter)
}
}
impl Clone for Lifetime {
fn clone(&self) -> Self {
Lifetime {
apostrophe: self.apostrophe,
ident: self.ident.clone(),
}
}
}
impl PartialEq for Lifetime {
fn eq(&self, other: &Lifetime) -> bool {
self.ident.eq(&other.ident)
}
}
impl Eq for Lifetime {}
impl PartialOrd for Lifetime {
fn partial_cmp(&self, other: &Lifetime) -> Option<Ordering> {
Some(self.cmp(other))
}
}
impl Ord for Lifetime {
fn cmp(&self, other: &Lifetime) -> Ordering {
self.ident.cmp(&other.ident)
}
}
impl Hash for Lifetime {
fn hash<H: Hasher>(&self, h: &mut H) {
self.ident.hash(h);
}
}
#[cfg(feature = "parsing")]
pub_if_not_doc! {
#[doc(hidden)]
#[allow(non_snake_case)]
pub fn Lifetime(marker: lookahead::TokenMarker) -> Lifetime {
match marker {}
}
}
#[cfg(feature = "parsing")]
pub(crate) mod parsing {
use crate::error::Result;
use crate::lifetime::Lifetime;
use crate::parse::{Parse, ParseStream};
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for Lifetime {
fn parse(input: ParseStream) -> Result<Self> {
input.step(|cursor| {
cursor
.lifetime()
.ok_or_else(|| cursor.error("expected lifetime"))
})
}
}
}
#[cfg(feature = "printing")]
mod printing {
use crate::lifetime::Lifetime;
use proc_macro2::{Punct, Spacing, TokenStream};
use quote::{ToTokens, TokenStreamExt};
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for Lifetime {
fn to_tokens(&self, tokens: &mut TokenStream) {
let mut apostrophe = Punct::new('\'', Spacing::Joint);
apostrophe.set_span(self.apostrophe);
tokens.append(apostrophe);
self.ident.to_tokens(tokens);
}
}
}

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use crate::buffer::Cursor;
use crate::error::{self, Error};
use crate::sealed::lookahead::Sealed;
use crate::span::IntoSpans;
use crate::token::{CustomToken, Token};
use proc_macro2::{Delimiter, Span};
use std::cell::RefCell;
/// Support for checking the next token in a stream to decide how to parse.
///
/// An important advantage over [`ParseStream::peek`] is that here we
/// automatically construct an appropriate error message based on the token
/// alternatives that get peeked. If you are producing your own error message,
/// go ahead and use `ParseStream::peek` instead.
///
/// Use [`ParseStream::lookahead1`] to construct this object.
///
/// [`ParseStream::peek`]: crate::parse::ParseBuffer::peek
/// [`ParseStream::lookahead1`]: crate::parse::ParseBuffer::lookahead1
///
/// Consuming tokens from the source stream after constructing a lookahead
/// object does not also advance the lookahead object.
///
/// # Example
///
/// ```
/// use syn::{ConstParam, Ident, Lifetime, LifetimeParam, Result, Token, TypeParam};
/// use syn::parse::{Parse, ParseStream};
///
/// // A generic parameter, a single one of the comma-separated elements inside
/// // angle brackets in:
/// //
/// // fn f<T: Clone, 'a, 'b: 'a, const N: usize>() { ... }
/// //
/// // On invalid input, lookahead gives us a reasonable error message.
/// //
/// // error: expected one of: identifier, lifetime, `const`
/// // |
/// // 5 | fn f<!Sized>() {}
/// // | ^
/// enum GenericParam {
/// Type(TypeParam),
/// Lifetime(LifetimeParam),
/// Const(ConstParam),
/// }
///
/// impl Parse for GenericParam {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let lookahead = input.lookahead1();
/// if lookahead.peek(Ident) {
/// input.parse().map(GenericParam::Type)
/// } else if lookahead.peek(Lifetime) {
/// input.parse().map(GenericParam::Lifetime)
/// } else if lookahead.peek(Token![const]) {
/// input.parse().map(GenericParam::Const)
/// } else {
/// Err(lookahead.error())
/// }
/// }
/// }
/// ```
pub struct Lookahead1<'a> {
scope: Span,
cursor: Cursor<'a>,
comparisons: RefCell<Vec<&'static str>>,
}
pub(crate) fn new(scope: Span, cursor: Cursor) -> Lookahead1 {
Lookahead1 {
scope,
cursor,
comparisons: RefCell::new(Vec::new()),
}
}
fn peek_impl(
lookahead: &Lookahead1,
peek: fn(Cursor) -> bool,
display: fn() -> &'static str,
) -> bool {
if peek(lookahead.cursor) {
return true;
}
lookahead.comparisons.borrow_mut().push(display());
false
}
impl<'a> Lookahead1<'a> {
/// Looks at the next token in the parse stream to determine whether it
/// matches the requested type of token.
///
/// # Syntax
///
/// Note that this method does not use turbofish syntax. Pass the peek type
/// inside of parentheses.
///
/// - `input.peek(Token![struct])`
/// - `input.peek(Token![==])`
/// - `input.peek(Ident)`&emsp;*(does not accept keywords)*
/// - `input.peek(Ident::peek_any)`
/// - `input.peek(Lifetime)`
/// - `input.peek(token::Brace)`
pub fn peek<T: Peek>(&self, token: T) -> bool {
let _ = token;
peek_impl(self, T::Token::peek, T::Token::display)
}
/// Triggers an error at the current position of the parse stream.
///
/// The error message will identify all of the expected token types that
/// have been peeked against this lookahead instance.
pub fn error(self) -> Error {
let mut comparisons = self.comparisons.into_inner();
comparisons.retain_mut(|display| {
if *display == "`)`" {
*display = match self.cursor.scope_delimiter() {
Delimiter::Parenthesis => "`)`",
Delimiter::Brace => "`}`",
Delimiter::Bracket => "`]`",
Delimiter::None => return false,
}
}
true
});
match comparisons.len() {
0 => {
if self.cursor.eof() {
Error::new(self.scope, "unexpected end of input")
} else {
Error::new(self.cursor.span(), "unexpected token")
}
}
1 => {
let message = format!("expected {}", comparisons[0]);
error::new_at(self.scope, self.cursor, message)
}
2 => {
let message = format!("expected {} or {}", comparisons[0], comparisons[1]);
error::new_at(self.scope, self.cursor, message)
}
_ => {
let join = comparisons.join(", ");
let message = format!("expected one of: {}", join);
error::new_at(self.scope, self.cursor, message)
}
}
}
}
/// Types that can be parsed by looking at just one token.
///
/// Use [`ParseStream::peek`] to peek one of these types in a parse stream
/// without consuming it from the stream.
///
/// This trait is sealed and cannot be implemented for types outside of Syn.
///
/// [`ParseStream::peek`]: crate::parse::ParseBuffer::peek
pub trait Peek: Sealed {
// Not public API.
#[doc(hidden)]
type Token: Token;
}
/// Pseudo-token used for peeking the end of a parse stream.
///
/// This type is only useful as an argument to one of the following functions:
///
/// - [`ParseStream::peek`][crate::parse::ParseBuffer::peek]
/// - [`ParseStream::peek2`][crate::parse::ParseBuffer::peek2]
/// - [`ParseStream::peek3`][crate::parse::ParseBuffer::peek3]
/// - [`Lookahead1::peek`]
///
/// The peek will return `true` if there are no remaining tokens after that
/// point in the parse stream.
///
/// # Example
///
/// Suppose we are parsing attributes containing core::fmt inspired formatting
/// arguments:
///
/// - `#[fmt("simple example")]`
/// - `#[fmt("interpolation e{}ample", self.x)]`
/// - `#[fmt("interpolation e{x}ample")]`
///
/// and we want to recognize the cases where no interpolation occurs so that
/// more efficient code can be generated.
///
/// The following implementation uses `input.peek(Token![,]) &&
/// input.peek2(End)` to recognize the case of a trailing comma without
/// consuming the comma from the parse stream, because if it isn't a trailing
/// comma, that same comma needs to be parsed as part of `args`.
///
/// ```
/// use proc_macro2::TokenStream;
/// use quote::quote;
/// use syn::parse::{End, Parse, ParseStream, Result};
/// use syn::{parse_quote, Attribute, LitStr, Token};
///
/// struct FormatArgs {
/// template: LitStr, // "...{}..."
/// args: TokenStream, // , self.x
/// }
///
/// impl Parse for FormatArgs {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let template: LitStr = input.parse()?;
///
/// let args = if input.is_empty()
/// || input.peek(Token![,]) && input.peek2(End)
/// {
/// input.parse::<Option<Token![,]>>()?;
/// TokenStream::new()
/// } else {
/// input.parse()?
/// };
///
/// Ok(FormatArgs {
/// template,
/// args,
/// })
/// }
/// }
///
/// fn main() -> Result<()> {
/// let attrs: Vec<Attribute> = parse_quote! {
/// #[fmt("simple example")]
/// #[fmt("interpolation e{}ample", self.x)]
/// #[fmt("interpolation e{x}ample")]
/// };
///
/// for attr in &attrs {
/// let FormatArgs { template, args } = attr.parse_args()?;
/// let requires_fmt_machinery =
/// !args.is_empty() || template.value().contains(['{', '}']);
/// let out = if requires_fmt_machinery {
/// quote! {
/// ::core::write!(__formatter, #template #args)
/// }
/// } else {
/// quote! {
/// __formatter.write_str(#template)
/// }
/// };
/// println!("{}", out);
/// }
/// Ok(())
/// }
/// ```
///
/// Implementing this parsing logic without `peek2(End)` is more clumsy because
/// we'd need a parse stream actually advanced past the comma before being able
/// to find out whether there is anything after it. It would look something
/// like:
///
/// ```
/// # use proc_macro2::TokenStream;
/// # use syn::parse::{ParseStream, Result};
/// # use syn::Token;
/// #
/// # fn parse(input: ParseStream) -> Result<()> {
/// use syn::parse::discouraged::Speculative as _;
///
/// let ahead = input.fork();
/// ahead.parse::<Option<Token![,]>>()?;
/// let args = if ahead.is_empty() {
/// input.advance_to(&ahead);
/// TokenStream::new()
/// } else {
/// input.parse()?
/// };
/// # Ok(())
/// # }
/// ```
///
/// or:
///
/// ```
/// # use proc_macro2::TokenStream;
/// # use syn::parse::{ParseStream, Result};
/// # use syn::Token;
/// #
/// # fn parse(input: ParseStream) -> Result<()> {
/// use quote::ToTokens as _;
///
/// let comma: Option<Token![,]> = input.parse()?;
/// let mut args = TokenStream::new();
/// if !input.is_empty() {
/// comma.to_tokens(&mut args);
/// input.parse::<TokenStream>()?.to_tokens(&mut args);
/// }
/// # Ok(())
/// # }
/// ```
pub struct End;
impl Copy for End {}
impl Clone for End {
fn clone(&self) -> Self {
*self
}
}
impl Peek for End {
type Token = Self;
}
impl CustomToken for End {
fn peek(cursor: Cursor) -> bool {
cursor.eof()
}
fn display() -> &'static str {
"`)`" // Lookahead1 error message will fill in the expected close delimiter
}
}
impl<F: Copy + FnOnce(TokenMarker) -> T, T: Token> Peek for F {
type Token = T;
}
pub enum TokenMarker {}
impl<S> IntoSpans<S> for TokenMarker {
fn into_spans(self) -> S {
match self {}
}
}
impl<F: Copy + FnOnce(TokenMarker) -> T, T: Token> Sealed for F {}
impl Sealed for End {}

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#[cfg(feature = "parsing")]
use crate::error::Result;
#[cfg(feature = "parsing")]
use crate::parse::{Parse, ParseStream, Parser};
use crate::path::Path;
use crate::token::{Brace, Bracket, Paren};
use proc_macro2::extra::DelimSpan;
#[cfg(feature = "parsing")]
use proc_macro2::Delimiter;
use proc_macro2::TokenStream;
#[cfg(feature = "parsing")]
use proc_macro2::TokenTree;
ast_struct! {
/// A macro invocation: `println!("{}", mac)`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct Macro {
pub path: Path,
pub bang_token: Token![!],
pub delimiter: MacroDelimiter,
pub tokens: TokenStream,
}
}
ast_enum! {
/// A grouping token that surrounds a macro body: `m!(...)` or `m!{...}` or `m![...]`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub enum MacroDelimiter {
Paren(Paren),
Brace(Brace),
Bracket(Bracket),
}
}
impl MacroDelimiter {
pub fn span(&self) -> &DelimSpan {
match self {
MacroDelimiter::Paren(token) => &token.span,
MacroDelimiter::Brace(token) => &token.span,
MacroDelimiter::Bracket(token) => &token.span,
}
}
#[cfg(all(feature = "full", any(feature = "parsing", feature = "printing")))]
pub(crate) fn is_brace(&self) -> bool {
match self {
MacroDelimiter::Brace(_) => true,
MacroDelimiter::Paren(_) | MacroDelimiter::Bracket(_) => false,
}
}
}
impl Macro {
/// Parse the tokens within the macro invocation's delimiters into a syntax
/// tree.
///
/// This is equivalent to `syn::parse2::<T>(mac.tokens)` except that it
/// produces a more useful span when `tokens` is empty.
///
/// # Example
///
/// ```
/// use syn::{parse_quote, Expr, ExprLit, Ident, Lit, LitStr, Macro, Token};
/// use syn::ext::IdentExt;
/// use syn::parse::{Error, Parse, ParseStream, Result};
/// use syn::punctuated::Punctuated;
///
/// // The arguments expected by libcore's format_args macro, and as a
/// // result most other formatting and printing macros like println.
/// //
/// // println!("{} is {number:.prec$}", "x", prec=5, number=0.01)
/// struct FormatArgs {
/// format_string: Expr,
/// positional_args: Vec<Expr>,
/// named_args: Vec<(Ident, Expr)>,
/// }
///
/// impl Parse for FormatArgs {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let format_string: Expr;
/// let mut positional_args = Vec::new();
/// let mut named_args = Vec::new();
///
/// format_string = input.parse()?;
/// while !input.is_empty() {
/// input.parse::<Token![,]>()?;
/// if input.is_empty() {
/// break;
/// }
/// if input.peek(Ident::peek_any) && input.peek2(Token![=]) {
/// while !input.is_empty() {
/// let name: Ident = input.call(Ident::parse_any)?;
/// input.parse::<Token![=]>()?;
/// let value: Expr = input.parse()?;
/// named_args.push((name, value));
/// if input.is_empty() {
/// break;
/// }
/// input.parse::<Token![,]>()?;
/// }
/// break;
/// }
/// positional_args.push(input.parse()?);
/// }
///
/// Ok(FormatArgs {
/// format_string,
/// positional_args,
/// named_args,
/// })
/// }
/// }
///
/// // Extract the first argument, the format string literal, from an
/// // invocation of a formatting or printing macro.
/// fn get_format_string(m: &Macro) -> Result<LitStr> {
/// let args: FormatArgs = m.parse_body()?;
/// match args.format_string {
/// Expr::Lit(ExprLit { lit: Lit::Str(lit), .. }) => Ok(lit),
/// other => {
/// // First argument was not a string literal expression.
/// // Maybe something like: println!(concat!(...), ...)
/// Err(Error::new_spanned(other, "format string must be a string literal"))
/// }
/// }
/// }
///
/// fn main() {
/// let invocation = parse_quote! {
/// println!("{:?}", Instant::now())
/// };
/// let lit = get_format_string(&invocation).unwrap();
/// assert_eq!(lit.value(), "{:?}");
/// }
/// ```
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_body<T: Parse>(&self) -> Result<T> {
self.parse_body_with(T::parse)
}
/// Parse the tokens within the macro invocation's delimiters using the
/// given parser.
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_body_with<F: Parser>(&self, parser: F) -> Result<F::Output> {
let scope = self.delimiter.span().close();
crate::parse::parse_scoped(parser, scope, self.tokens.clone())
}
}
#[cfg(feature = "parsing")]
pub(crate) fn parse_delimiter(input: ParseStream) -> Result<(MacroDelimiter, TokenStream)> {
input.step(|cursor| {
if let Some((TokenTree::Group(g), rest)) = cursor.token_tree() {
let span = g.delim_span();
let delimiter = match g.delimiter() {
Delimiter::Parenthesis => MacroDelimiter::Paren(Paren(span)),
Delimiter::Brace => MacroDelimiter::Brace(Brace(span)),
Delimiter::Bracket => MacroDelimiter::Bracket(Bracket(span)),
Delimiter::None => {
return Err(cursor.error("expected delimiter"));
}
};
Ok(((delimiter, g.stream()), rest))
} else {
Err(cursor.error("expected delimiter"))
}
})
}
#[cfg(feature = "parsing")]
pub(crate) mod parsing {
use crate::error::Result;
use crate::mac::{parse_delimiter, Macro};
use crate::parse::{Parse, ParseStream};
use crate::path::Path;
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for Macro {
fn parse(input: ParseStream) -> Result<Self> {
let tokens;
Ok(Macro {
path: input.call(Path::parse_mod_style)?,
bang_token: input.parse()?,
delimiter: {
let (delimiter, content) = parse_delimiter(input)?;
tokens = content;
delimiter
},
tokens,
})
}
}
}
#[cfg(feature = "printing")]
mod printing {
use crate::mac::{Macro, MacroDelimiter};
use crate::path;
use crate::path::printing::PathStyle;
use crate::token;
use proc_macro2::{Delimiter, TokenStream};
use quote::ToTokens;
impl MacroDelimiter {
pub(crate) fn surround(&self, tokens: &mut TokenStream, inner: TokenStream) {
let (delim, span) = match self {
MacroDelimiter::Paren(paren) => (Delimiter::Parenthesis, paren.span),
MacroDelimiter::Brace(brace) => (Delimiter::Brace, brace.span),
MacroDelimiter::Bracket(bracket) => (Delimiter::Bracket, bracket.span),
};
token::printing::delim(delim, span.join(), tokens, inner);
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for Macro {
fn to_tokens(&self, tokens: &mut TokenStream) {
path::printing::print_path(tokens, &self.path, PathStyle::Mod);
self.bang_token.to_tokens(tokens);
self.delimiter.surround(tokens, self.tokens.clone());
}
}
}

182
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#[cfg_attr(
not(any(feature = "full", feature = "derive")),
allow(unknown_lints, unused_macro_rules)
)]
macro_rules! ast_struct {
(
$(#[$attr:meta])*
$pub:ident $struct:ident $name:ident #full $body:tt
) => {
check_keyword_matches!(pub $pub);
check_keyword_matches!(struct $struct);
#[cfg(feature = "full")]
$(#[$attr])* $pub $struct $name $body
#[cfg(not(feature = "full"))]
$(#[$attr])* $pub $struct $name {
_noconstruct: ::std::marker::PhantomData<::proc_macro2::Span>,
}
#[cfg(all(not(feature = "full"), feature = "printing"))]
impl ::quote::ToTokens for $name {
fn to_tokens(&self, _: &mut ::proc_macro2::TokenStream) {
unreachable!()
}
}
};
(
$(#[$attr:meta])*
$pub:ident $struct:ident $name:ident $body:tt
) => {
check_keyword_matches!(pub $pub);
check_keyword_matches!(struct $struct);
$(#[$attr])* $pub $struct $name $body
};
}
#[cfg(any(feature = "full", feature = "derive"))]
macro_rules! ast_enum {
(
$(#[$enum_attr:meta])*
$pub:ident $enum:ident $name:ident $body:tt
) => {
check_keyword_matches!(pub $pub);
check_keyword_matches!(enum $enum);
$(#[$enum_attr])* $pub $enum $name $body
};
}
macro_rules! ast_enum_of_structs {
(
$(#[$enum_attr:meta])*
$pub:ident $enum:ident $name:ident $body:tt
) => {
check_keyword_matches!(pub $pub);
check_keyword_matches!(enum $enum);
$(#[$enum_attr])* $pub $enum $name $body
ast_enum_of_structs_impl!($name $body);
#[cfg(feature = "printing")]
generate_to_tokens!(() tokens $name $body);
};
}
macro_rules! ast_enum_of_structs_impl {
(
$name:ident {
$(
$(#[cfg $cfg_attr:tt])*
$(#[doc $($doc_attr:tt)*])*
$variant:ident $( ($member:ident) )*,
)*
}
) => {
$($(
ast_enum_from_struct!($name::$variant, $member);
)*)*
};
}
macro_rules! ast_enum_from_struct {
// No From<TokenStream> for verbatim variants.
($name:ident::Verbatim, $member:ident) => {};
($name:ident::$variant:ident, $member:ident) => {
impl From<$member> for $name {
fn from(e: $member) -> $name {
$name::$variant(e)
}
}
};
}
#[cfg(feature = "printing")]
macro_rules! generate_to_tokens {
(
($($arms:tt)*) $tokens:ident $name:ident {
$(#[cfg $cfg_attr:tt])*
$(#[doc $($doc_attr:tt)*])*
$variant:ident,
$($next:tt)*
}
) => {
generate_to_tokens!(
($($arms)* $(#[cfg $cfg_attr])* $name::$variant => {})
$tokens $name { $($next)* }
);
};
(
($($arms:tt)*) $tokens:ident $name:ident {
$(#[cfg $cfg_attr:tt])*
$(#[doc $($doc_attr:tt)*])*
$variant:ident($member:ident),
$($next:tt)*
}
) => {
generate_to_tokens!(
($($arms)* $(#[cfg $cfg_attr])* $name::$variant(_e) => _e.to_tokens($tokens),)
$tokens $name { $($next)* }
);
};
(($($arms:tt)*) $tokens:ident $name:ident {}) => {
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ::quote::ToTokens for $name {
fn to_tokens(&self, $tokens: &mut ::proc_macro2::TokenStream) {
match self {
$($arms)*
}
}
}
};
}
// Rustdoc bug: does not respect the doc(hidden) on some items.
#[cfg(all(doc, feature = "parsing"))]
macro_rules! pub_if_not_doc {
($(#[$m:meta])* $pub:ident $($item:tt)*) => {
check_keyword_matches!(pub $pub);
$(#[$m])*
$pub(crate) $($item)*
};
}
#[cfg(all(not(doc), feature = "parsing"))]
macro_rules! pub_if_not_doc {
($(#[$m:meta])* $pub:ident $($item:tt)*) => {
check_keyword_matches!(pub $pub);
$(#[$m])*
$pub $($item)*
};
}
macro_rules! check_keyword_matches {
(enum enum) => {};
(pub pub) => {};
(struct struct) => {};
}
#[cfg(any(feature = "full", feature = "derive"))]
macro_rules! return_impl_trait {
(
$(#[$attr:meta])*
$vis:vis fn $name:ident $args:tt -> $impl_trait:ty [$concrete:ty] $body:block
) => {
#[cfg(not(docsrs))]
$(#[$attr])*
$vis fn $name $args -> $concrete $body
#[cfg(docsrs)]
$(#[$attr])*
$vis fn $name $args -> $impl_trait $body
};
}

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//! Facility for interpreting structured content inside of an `Attribute`.
use crate::error::{Error, Result};
use crate::ext::IdentExt as _;
use crate::lit::Lit;
use crate::parse::{ParseStream, Parser};
use crate::path::{Path, PathSegment};
use crate::punctuated::Punctuated;
use proc_macro2::Ident;
use std::fmt::Display;
/// Make a parser that is usable with `parse_macro_input!` in a
/// `#[proc_macro_attribute]` macro.
///
/// *Warning:* When parsing attribute args **other than** the
/// `proc_macro::TokenStream` input of a `proc_macro_attribute`, you do **not**
/// need this function. In several cases your callers will get worse error
/// messages if you use this function, because the surrounding delimiter's span
/// is concealed from attribute macros by rustc. Use
/// [`Attribute::parse_nested_meta`] instead.
///
/// [`Attribute::parse_nested_meta`]: crate::Attribute::parse_nested_meta
///
/// # Example
///
/// This example implements an attribute macro whose invocations look like this:
///
/// ```
/// # const IGNORE: &str = stringify! {
/// #[tea(kind = "EarlGrey", hot)]
/// struct Picard {...}
/// # };
/// ```
///
/// The "parameters" supported by the attribute are:
///
/// - `kind = "..."`
/// - `hot`
/// - `with(sugar, milk, ...)`, a comma-separated list of ingredients
///
/// ```
/// # extern crate proc_macro;
/// #
/// use proc_macro::TokenStream;
/// use syn::{parse_macro_input, LitStr, Path};
///
/// # const IGNORE: &str = stringify! {
/// #[proc_macro_attribute]
/// # };
/// pub fn tea(args: TokenStream, input: TokenStream) -> TokenStream {
/// let mut kind: Option<LitStr> = None;
/// let mut hot: bool = false;
/// let mut with: Vec<Path> = Vec::new();
/// let tea_parser = syn::meta::parser(|meta| {
/// if meta.path.is_ident("kind") {
/// kind = Some(meta.value()?.parse()?);
/// Ok(())
/// } else if meta.path.is_ident("hot") {
/// hot = true;
/// Ok(())
/// } else if meta.path.is_ident("with") {
/// meta.parse_nested_meta(|meta| {
/// with.push(meta.path);
/// Ok(())
/// })
/// } else {
/// Err(meta.error("unsupported tea property"))
/// }
/// });
///
/// parse_macro_input!(args with tea_parser);
/// eprintln!("kind={kind:?} hot={hot} with={with:?}");
///
/// /* ... */
/// # TokenStream::new()
/// }
/// ```
///
/// The `syn::meta` library will take care of dealing with the commas including
/// trailing commas, and producing sensible error messages on unexpected input.
///
/// ```console
/// error: expected `,`
/// --> src/main.rs:3:37
/// |
/// 3 | #[tea(kind = "EarlGrey", with(sugar = "lol", milk))]
/// | ^
/// ```
///
/// # Example
///
/// Same as above but we factor out most of the logic into a separate function.
///
/// ```
/// # extern crate proc_macro;
/// #
/// use proc_macro::TokenStream;
/// use syn::meta::ParseNestedMeta;
/// use syn::parse::{Parser, Result};
/// use syn::{parse_macro_input, LitStr, Path};
///
/// # const IGNORE: &str = stringify! {
/// #[proc_macro_attribute]
/// # };
/// pub fn tea(args: TokenStream, input: TokenStream) -> TokenStream {
/// let mut attrs = TeaAttributes::default();
/// let tea_parser = syn::meta::parser(|meta| attrs.parse(meta));
/// parse_macro_input!(args with tea_parser);
///
/// /* ... */
/// # TokenStream::new()
/// }
///
/// #[derive(Default)]
/// struct TeaAttributes {
/// kind: Option<LitStr>,
/// hot: bool,
/// with: Vec<Path>,
/// }
///
/// impl TeaAttributes {
/// fn parse(&mut self, meta: ParseNestedMeta) -> Result<()> {
/// if meta.path.is_ident("kind") {
/// self.kind = Some(meta.value()?.parse()?);
/// Ok(())
/// } else /* just like in last example */
/// # { unimplemented!() }
///
/// }
/// }
/// ```
pub fn parser(logic: impl FnMut(ParseNestedMeta) -> Result<()>) -> impl Parser<Output = ()> {
|input: ParseStream| {
if input.is_empty() {
Ok(())
} else {
parse_nested_meta(input, logic)
}
}
}
/// Context for parsing a single property in the conventional syntax for
/// structured attributes.
///
/// # Examples
///
/// Refer to usage examples on the following two entry-points:
///
/// - [`Attribute::parse_nested_meta`] if you have an entire `Attribute` to
/// parse. Always use this if possible. Generally this is able to produce
/// better error messages because `Attribute` holds span information for all
/// of the delimiters therein.
///
/// - [`syn::meta::parser`] if you are implementing a `proc_macro_attribute`
/// macro and parsing the arguments to the attribute macro, i.e. the ones
/// written in the same attribute that dispatched the macro invocation. Rustc
/// does not pass span information for the surrounding delimiters into the
/// attribute macro invocation in this situation, so error messages might be
/// less precise.
///
/// [`Attribute::parse_nested_meta`]: crate::Attribute::parse_nested_meta
/// [`syn::meta::parser`]: crate::meta::parser
#[non_exhaustive]
pub struct ParseNestedMeta<'a> {
pub path: Path,
pub input: ParseStream<'a>,
}
impl<'a> ParseNestedMeta<'a> {
/// Used when parsing `key = "value"` syntax.
///
/// All it does is advance `meta.input` past the `=` sign in the input. You
/// could accomplish the same effect by writing
/// `meta.parse::<Token![=]>()?`, so at most it is a minor convenience to
/// use `meta.value()?`.
///
/// # Example
///
/// ```
/// use syn::{parse_quote, Attribute, LitStr};
///
/// let attr: Attribute = parse_quote! {
/// #[tea(kind = "EarlGrey")]
/// };
/// // conceptually:
/// if attr.path().is_ident("tea") { // this parses the `tea`
/// attr.parse_nested_meta(|meta| { // this parses the `(`
/// if meta.path.is_ident("kind") { // this parses the `kind`
/// let value = meta.value()?; // this parses the `=`
/// let s: LitStr = value.parse()?; // this parses `"EarlGrey"`
/// if s.value() == "EarlGrey" {
/// // ...
/// }
/// Ok(())
/// } else {
/// Err(meta.error("unsupported attribute"))
/// }
/// })?;
/// }
/// # anyhow::Ok(())
/// ```
pub fn value(&self) -> Result<ParseStream<'a>> {
self.input.parse::<Token![=]>()?;
Ok(self.input)
}
/// Used when parsing `list(...)` syntax **if** the content inside the
/// nested parentheses is also expected to conform to Rust's structured
/// attribute convention.
///
/// # Example
///
/// ```
/// use syn::{parse_quote, Attribute};
///
/// let attr: Attribute = parse_quote! {
/// #[tea(with(sugar, milk))]
/// };
///
/// if attr.path().is_ident("tea") {
/// attr.parse_nested_meta(|meta| {
/// if meta.path.is_ident("with") {
/// meta.parse_nested_meta(|meta| { // <---
/// if meta.path.is_ident("sugar") {
/// // Here we can go even deeper if needed.
/// Ok(())
/// } else if meta.path.is_ident("milk") {
/// Ok(())
/// } else {
/// Err(meta.error("unsupported ingredient"))
/// }
/// })
/// } else {
/// Err(meta.error("unsupported tea property"))
/// }
/// })?;
/// }
/// # anyhow::Ok(())
/// ```
///
/// # Counterexample
///
/// If you don't need `parse_nested_meta`'s help in parsing the content
/// written within the nested parentheses, keep in mind that you can always
/// just parse it yourself from the exposed ParseStream. Rust syntax permits
/// arbitrary tokens within those parentheses so for the crazier stuff,
/// `parse_nested_meta` is not what you want.
///
/// ```
/// use syn::{parenthesized, parse_quote, Attribute, LitInt};
///
/// let attr: Attribute = parse_quote! {
/// #[repr(align(32))]
/// };
///
/// let mut align: Option<LitInt> = None;
/// if attr.path().is_ident("repr") {
/// attr.parse_nested_meta(|meta| {
/// if meta.path.is_ident("align") {
/// let content;
/// parenthesized!(content in meta.input);
/// align = Some(content.parse()?);
/// Ok(())
/// } else {
/// Err(meta.error("unsupported repr"))
/// }
/// })?;
/// }
/// # anyhow::Ok(())
/// ```
pub fn parse_nested_meta(
&self,
logic: impl FnMut(ParseNestedMeta) -> Result<()>,
) -> Result<()> {
let content;
parenthesized!(content in self.input);
parse_nested_meta(&content, logic)
}
/// Report that the attribute's content did not conform to expectations.
///
/// The span of the resulting error will cover `meta.path` *and* everything
/// that has been parsed so far since it.
///
/// There are 2 ways you might call this. First, if `meta.path` is not
/// something you recognize:
///
/// ```
/// # use syn::Attribute;
/// #
/// # fn example(attr: &Attribute) -> syn::Result<()> {
/// attr.parse_nested_meta(|meta| {
/// if meta.path.is_ident("kind") {
/// // ...
/// Ok(())
/// } else {
/// Err(meta.error("unsupported tea property"))
/// }
/// })?;
/// # Ok(())
/// # }
/// ```
///
/// In this case, it behaves exactly like
/// `syn::Error::new_spanned(&meta.path, "message...")`.
///
/// ```console
/// error: unsupported tea property
/// --> src/main.rs:3:26
/// |
/// 3 | #[tea(kind = "EarlGrey", wat = "foo")]
/// | ^^^
/// ```
///
/// More usefully, the second place is if you've already parsed a value but
/// have decided not to accept the value:
///
/// ```
/// # use syn::Attribute;
/// #
/// # fn example(attr: &Attribute) -> syn::Result<()> {
/// use syn::Expr;
///
/// attr.parse_nested_meta(|meta| {
/// if meta.path.is_ident("kind") {
/// let expr: Expr = meta.value()?.parse()?;
/// match expr {
/// Expr::Lit(expr) => /* ... */
/// # unimplemented!(),
/// Expr::Path(expr) => /* ... */
/// # unimplemented!(),
/// Expr::Macro(expr) => /* ... */
/// # unimplemented!(),
/// _ => Err(meta.error("tea kind must be a string literal, path, or macro")),
/// }
/// } else /* as above */
/// # { unimplemented!() }
///
/// })?;
/// # Ok(())
/// # }
/// ```
///
/// ```console
/// error: tea kind must be a string literal, path, or macro
/// --> src/main.rs:3:7
/// |
/// 3 | #[tea(kind = async { replicator.await })]
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/// ```
///
/// Often you may want to use `syn::Error::new_spanned` even in this
/// situation. In the above code, that would be:
///
/// ```
/// # use syn::{Error, Expr};
/// #
/// # fn example(expr: Expr) -> syn::Result<()> {
/// match expr {
/// Expr::Lit(expr) => /* ... */
/// # unimplemented!(),
/// Expr::Path(expr) => /* ... */
/// # unimplemented!(),
/// Expr::Macro(expr) => /* ... */
/// # unimplemented!(),
/// _ => Err(Error::new_spanned(expr, "unsupported expression type for `kind`")),
/// }
/// # }
/// ```
///
/// ```console
/// error: unsupported expression type for `kind`
/// --> src/main.rs:3:14
/// |
/// 3 | #[tea(kind = async { replicator.await })]
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^
/// ```
pub fn error(&self, msg: impl Display) -> Error {
let start_span = self.path.segments[0].ident.span();
let end_span = self.input.cursor().prev_span();
crate::error::new2(start_span, end_span, msg)
}
}
pub(crate) fn parse_nested_meta(
input: ParseStream,
mut logic: impl FnMut(ParseNestedMeta) -> Result<()>,
) -> Result<()> {
loop {
let path = input.call(parse_meta_path)?;
logic(ParseNestedMeta { path, input })?;
if input.is_empty() {
return Ok(());
}
input.parse::<Token![,]>()?;
if input.is_empty() {
return Ok(());
}
}
}
// Like Path::parse_mod_style, but accepts keywords in the path.
fn parse_meta_path(input: ParseStream) -> Result<Path> {
Ok(Path {
leading_colon: input.parse()?,
segments: {
let mut segments = Punctuated::new();
if input.peek(Ident::peek_any) {
let ident = Ident::parse_any(input)?;
segments.push_value(PathSegment::from(ident));
} else if input.is_empty() {
return Err(input.error("expected nested attribute"));
} else if input.peek(Lit) {
return Err(input.error("unexpected literal in nested attribute, expected ident"));
} else {
return Err(input.error("unexpected token in nested attribute, expected ident"));
}
while input.peek(Token![::]) {
let punct = input.parse()?;
segments.push_punct(punct);
let ident = Ident::parse_any(input)?;
segments.push_value(PathSegment::from(ident));
}
segments
},
})
}

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rust/syn/op.rs Normal file
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ast_enum! {
/// A binary operator: `+`, `+=`, `&`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
#[non_exhaustive]
pub enum BinOp {
/// The `+` operator (addition)
Add(Token![+]),
/// The `-` operator (subtraction)
Sub(Token![-]),
/// The `*` operator (multiplication)
Mul(Token![*]),
/// The `/` operator (division)
Div(Token![/]),
/// The `%` operator (modulus)
Rem(Token![%]),
/// The `&&` operator (logical and)
And(Token![&&]),
/// The `||` operator (logical or)
Or(Token![||]),
/// The `^` operator (bitwise xor)
BitXor(Token![^]),
/// The `&` operator (bitwise and)
BitAnd(Token![&]),
/// The `|` operator (bitwise or)
BitOr(Token![|]),
/// The `<<` operator (shift left)
Shl(Token![<<]),
/// The `>>` operator (shift right)
Shr(Token![>>]),
/// The `==` operator (equality)
Eq(Token![==]),
/// The `<` operator (less than)
Lt(Token![<]),
/// The `<=` operator (less than or equal to)
Le(Token![<=]),
/// The `!=` operator (not equal to)
Ne(Token![!=]),
/// The `>=` operator (greater than or equal to)
Ge(Token![>=]),
/// The `>` operator (greater than)
Gt(Token![>]),
/// The `+=` operator
AddAssign(Token![+=]),
/// The `-=` operator
SubAssign(Token![-=]),
/// The `*=` operator
MulAssign(Token![*=]),
/// The `/=` operator
DivAssign(Token![/=]),
/// The `%=` operator
RemAssign(Token![%=]),
/// The `^=` operator
BitXorAssign(Token![^=]),
/// The `&=` operator
BitAndAssign(Token![&=]),
/// The `|=` operator
BitOrAssign(Token![|=]),
/// The `<<=` operator
ShlAssign(Token![<<=]),
/// The `>>=` operator
ShrAssign(Token![>>=]),
}
}
ast_enum! {
/// A unary operator: `*`, `!`, `-`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
#[non_exhaustive]
pub enum UnOp {
/// The `*` operator for dereferencing
Deref(Token![*]),
/// The `!` operator for logical inversion
Not(Token![!]),
/// The `-` operator for negation
Neg(Token![-]),
}
}
#[cfg(feature = "parsing")]
pub(crate) mod parsing {
use crate::error::Result;
use crate::op::{BinOp, UnOp};
use crate::parse::{Parse, ParseStream};
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for BinOp {
fn parse(input: ParseStream) -> Result<Self> {
if input.peek(Token![+=]) {
input.parse().map(BinOp::AddAssign)
} else if input.peek(Token![-=]) {
input.parse().map(BinOp::SubAssign)
} else if input.peek(Token![*=]) {
input.parse().map(BinOp::MulAssign)
} else if input.peek(Token![/=]) {
input.parse().map(BinOp::DivAssign)
} else if input.peek(Token![%=]) {
input.parse().map(BinOp::RemAssign)
} else if input.peek(Token![^=]) {
input.parse().map(BinOp::BitXorAssign)
} else if input.peek(Token![&=]) {
input.parse().map(BinOp::BitAndAssign)
} else if input.peek(Token![|=]) {
input.parse().map(BinOp::BitOrAssign)
} else if input.peek(Token![<<=]) {
input.parse().map(BinOp::ShlAssign)
} else if input.peek(Token![>>=]) {
input.parse().map(BinOp::ShrAssign)
} else if input.peek(Token![&&]) {
input.parse().map(BinOp::And)
} else if input.peek(Token![||]) {
input.parse().map(BinOp::Or)
} else if input.peek(Token![<<]) {
input.parse().map(BinOp::Shl)
} else if input.peek(Token![>>]) {
input.parse().map(BinOp::Shr)
} else if input.peek(Token![==]) {
input.parse().map(BinOp::Eq)
} else if input.peek(Token![<=]) {
input.parse().map(BinOp::Le)
} else if input.peek(Token![!=]) {
input.parse().map(BinOp::Ne)
} else if input.peek(Token![>=]) {
input.parse().map(BinOp::Ge)
} else if input.peek(Token![+]) {
input.parse().map(BinOp::Add)
} else if input.peek(Token![-]) {
input.parse().map(BinOp::Sub)
} else if input.peek(Token![*]) {
input.parse().map(BinOp::Mul)
} else if input.peek(Token![/]) {
input.parse().map(BinOp::Div)
} else if input.peek(Token![%]) {
input.parse().map(BinOp::Rem)
} else if input.peek(Token![^]) {
input.parse().map(BinOp::BitXor)
} else if input.peek(Token![&]) {
input.parse().map(BinOp::BitAnd)
} else if input.peek(Token![|]) {
input.parse().map(BinOp::BitOr)
} else if input.peek(Token![<]) {
input.parse().map(BinOp::Lt)
} else if input.peek(Token![>]) {
input.parse().map(BinOp::Gt)
} else {
Err(input.error("expected binary operator"))
}
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for UnOp {
fn parse(input: ParseStream) -> Result<Self> {
let lookahead = input.lookahead1();
if lookahead.peek(Token![*]) {
input.parse().map(UnOp::Deref)
} else if lookahead.peek(Token![!]) {
input.parse().map(UnOp::Not)
} else if lookahead.peek(Token![-]) {
input.parse().map(UnOp::Neg)
} else {
Err(lookahead.error())
}
}
}
}
#[cfg(feature = "printing")]
mod printing {
use crate::op::{BinOp, UnOp};
use proc_macro2::TokenStream;
use quote::ToTokens;
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for BinOp {
fn to_tokens(&self, tokens: &mut TokenStream) {
match self {
BinOp::Add(t) => t.to_tokens(tokens),
BinOp::Sub(t) => t.to_tokens(tokens),
BinOp::Mul(t) => t.to_tokens(tokens),
BinOp::Div(t) => t.to_tokens(tokens),
BinOp::Rem(t) => t.to_tokens(tokens),
BinOp::And(t) => t.to_tokens(tokens),
BinOp::Or(t) => t.to_tokens(tokens),
BinOp::BitXor(t) => t.to_tokens(tokens),
BinOp::BitAnd(t) => t.to_tokens(tokens),
BinOp::BitOr(t) => t.to_tokens(tokens),
BinOp::Shl(t) => t.to_tokens(tokens),
BinOp::Shr(t) => t.to_tokens(tokens),
BinOp::Eq(t) => t.to_tokens(tokens),
BinOp::Lt(t) => t.to_tokens(tokens),
BinOp::Le(t) => t.to_tokens(tokens),
BinOp::Ne(t) => t.to_tokens(tokens),
BinOp::Ge(t) => t.to_tokens(tokens),
BinOp::Gt(t) => t.to_tokens(tokens),
BinOp::AddAssign(t) => t.to_tokens(tokens),
BinOp::SubAssign(t) => t.to_tokens(tokens),
BinOp::MulAssign(t) => t.to_tokens(tokens),
BinOp::DivAssign(t) => t.to_tokens(tokens),
BinOp::RemAssign(t) => t.to_tokens(tokens),
BinOp::BitXorAssign(t) => t.to_tokens(tokens),
BinOp::BitAndAssign(t) => t.to_tokens(tokens),
BinOp::BitOrAssign(t) => t.to_tokens(tokens),
BinOp::ShlAssign(t) => t.to_tokens(tokens),
BinOp::ShrAssign(t) => t.to_tokens(tokens),
}
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for UnOp {
fn to_tokens(&self, tokens: &mut TokenStream) {
match self {
UnOp::Deref(t) => t.to_tokens(tokens),
UnOp::Not(t) => t.to_tokens(tokens),
UnOp::Neg(t) => t.to_tokens(tokens),
}
}
}
}

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/// Parse the input TokenStream of a macro, triggering a compile error if the
/// tokens fail to parse.
///
/// Refer to the [`parse` module] documentation for more details about parsing
/// in Syn.
///
/// [`parse` module]: mod@crate::parse
///
/// <br>
///
/// # Intended usage
///
/// This macro must be called from a function that returns
/// `proc_macro::TokenStream`. Usually this will be your proc macro entry point,
/// the function that has the #\[proc_macro\] / #\[proc_macro_derive\] /
/// #\[proc_macro_attribute\] attribute.
///
/// ```
/// # extern crate proc_macro;
/// #
/// use proc_macro::TokenStream;
/// use syn::{parse_macro_input, Result};
/// use syn::parse::{Parse, ParseStream};
///
/// struct MyMacroInput {
/// /* ... */
/// }
///
/// impl Parse for MyMacroInput {
/// fn parse(input: ParseStream) -> Result<Self> {
/// /* ... */
/// # Ok(MyMacroInput {})
/// }
/// }
///
/// # const IGNORE: &str = stringify! {
/// #[proc_macro]
/// # };
/// pub fn my_macro(tokens: TokenStream) -> TokenStream {
/// let input = parse_macro_input!(tokens as MyMacroInput);
///
/// /* ... */
/// # TokenStream::new()
/// }
/// ```
///
/// <br>
///
/// # Usage with Parser
///
/// This macro can also be used with the [`Parser` trait] for types that have
/// multiple ways that they can be parsed.
///
/// [`Parser` trait]: crate::parse::Parser
///
/// ```
/// # extern crate proc_macro;
/// #
/// # use proc_macro::TokenStream;
/// # use syn::{parse_macro_input, Result};
/// # use syn::parse::ParseStream;
/// #
/// # struct MyMacroInput {}
/// #
/// impl MyMacroInput {
/// fn parse_alternate(input: ParseStream) -> Result<Self> {
/// /* ... */
/// # Ok(MyMacroInput {})
/// }
/// }
///
/// # const IGNORE: &str = stringify! {
/// #[proc_macro]
/// # };
/// pub fn my_macro(tokens: TokenStream) -> TokenStream {
/// let input = parse_macro_input!(tokens with MyMacroInput::parse_alternate);
///
/// /* ... */
/// # TokenStream::new()
/// }
/// ```
///
/// <br>
///
/// # Expansion
///
/// `parse_macro_input!($variable as $Type)` expands to something like:
///
/// ```no_run
/// # extern crate proc_macro;
/// #
/// # macro_rules! doc_test {
/// # ($variable:ident as $Type:ty) => {
/// match syn::parse::<$Type>($variable) {
/// Ok(syntax_tree) => syntax_tree,
/// Err(err) => return proc_macro::TokenStream::from(err.to_compile_error()),
/// }
/// # };
/// # }
/// #
/// # fn test(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
/// # let _ = doc_test!(input as syn::Ident);
/// # proc_macro::TokenStream::new()
/// # }
/// ```
#[macro_export]
#[cfg_attr(docsrs, doc(cfg(all(feature = "parsing", feature = "proc-macro"))))]
macro_rules! parse_macro_input {
($tokenstream:ident as $ty:ty) => {
match $crate::parse::<$ty>($tokenstream) {
$crate::__private::Ok(data) => data,
$crate::__private::Err(err) => {
return $crate::__private::TokenStream::from(err.to_compile_error());
}
}
};
($tokenstream:ident with $parser:path) => {
match $crate::parse::Parser::parse($parser, $tokenstream) {
$crate::__private::Ok(data) => data,
$crate::__private::Err(err) => {
return $crate::__private::TokenStream::from(err.to_compile_error());
}
}
};
($tokenstream:ident) => {
$crate::parse_macro_input!($tokenstream as _)
};
}

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/// Quasi-quotation macro that accepts input like the [`quote!`] macro but uses
/// type inference to figure out a return type for those tokens.
///
/// [`quote!`]: https://docs.rs/quote/1.0/quote/index.html
///
/// The return type can be any syntax tree node that implements the [`Parse`]
/// trait.
///
/// [`Parse`]: crate::parse::Parse
///
/// ```
/// use quote::quote;
/// use syn::{parse_quote, Stmt};
///
/// fn main() {
/// let name = quote!(v);
/// let ty = quote!(u8);
///
/// let stmt: Stmt = parse_quote! {
/// let #name: #ty = Default::default();
/// };
///
/// println!("{:#?}", stmt);
/// }
/// ```
///
/// *This macro is available only if Syn is built with both the `"parsing"` and
/// `"printing"` features.*
///
/// # Example
///
/// The following helper function adds a bound `T: HeapSize` to every type
/// parameter `T` in the input generics.
///
/// ```
/// use syn::{parse_quote, Generics, GenericParam};
///
/// // Add a bound `T: HeapSize` to every type parameter T.
/// fn add_trait_bounds(mut generics: Generics) -> Generics {
/// for param in &mut generics.params {
/// if let GenericParam::Type(type_param) = param {
/// type_param.bounds.push(parse_quote!(HeapSize));
/// }
/// }
/// generics
/// }
/// ```
///
/// # Special cases
///
/// This macro can parse the following additional types as a special case even
/// though they do not implement the `Parse` trait.
///
/// - [`Attribute`] — parses one attribute, allowing either outer like `#[...]`
/// or inner like `#![...]`
/// - [`Vec<Attribute>`] — parses multiple attributes, including mixed kinds in
/// any order
/// - [`Punctuated<T, P>`] — parses zero or more `T` separated by punctuation
/// `P` with optional trailing punctuation
/// - [`Vec<Arm>`] — parses arms separated by optional commas according to the
/// same grammar as the inside of a `match` expression
/// - [`Vec<Stmt>`] — parses the same as `Block::parse_within`
/// - [`Pat`], [`Box<Pat>`] — parses the same as
/// `Pat::parse_multi_with_leading_vert`
/// - [`Field`] — parses a named or unnamed struct field
///
/// [`Vec<Attribute>`]: Attribute
/// [`Vec<Arm>`]: Arm
/// [`Vec<Stmt>`]: Block::parse_within
/// [`Pat`]: Pat::parse_multi_with_leading_vert
/// [`Box<Pat>`]: Pat::parse_multi_with_leading_vert
///
/// # Panics
///
/// Panics if the tokens fail to parse as the expected syntax tree type. The
/// caller is responsible for ensuring that the input tokens are syntactically
/// valid.
#[cfg_attr(docsrs, doc(cfg(all(feature = "parsing", feature = "printing"))))]
#[macro_export]
macro_rules! parse_quote {
($($tt:tt)*) => {
$crate::__private::parse_quote($crate::__private::quote::quote!($($tt)*))
};
}
/// This macro is [`parse_quote!`] + [`quote_spanned!`][quote::quote_spanned].
///
/// Please refer to each of their documentation.
///
/// # Example
///
/// ```
/// use quote::{quote, quote_spanned};
/// use syn::spanned::Spanned;
/// use syn::{parse_quote_spanned, ReturnType, Signature};
///
/// // Changes `fn()` to `fn() -> Pin<Box<dyn Future<Output = ()>>>`,
/// // and `fn() -> T` to `fn() -> Pin<Box<dyn Future<Output = T>>>`,
/// // without introducing any call_site() spans.
/// fn make_ret_pinned_future(sig: &mut Signature) {
/// let ret = match &sig.output {
/// ReturnType::Default => quote_spanned!(sig.paren_token.span=> ()),
/// ReturnType::Type(_, ret) => quote!(#ret),
/// };
/// sig.output = parse_quote_spanned! {ret.span()=>
/// -> ::std::pin::Pin<::std::boxed::Box<dyn ::std::future::Future<Output = #ret>>>
/// };
/// }
/// ```
#[cfg_attr(docsrs, doc(cfg(all(feature = "parsing", feature = "printing"))))]
#[macro_export]
macro_rules! parse_quote_spanned {
($span:expr=> $($tt:tt)*) => {
$crate::__private::parse_quote($crate::__private::quote::quote_spanned!($span=> $($tt)*))
};
}
////////////////////////////////////////////////////////////////////////////////
// Can parse any type that implements Parse.
use crate::error::Result;
use crate::parse::{Parse, ParseStream, Parser};
use proc_macro2::TokenStream;
// Not public API.
#[doc(hidden)]
#[track_caller]
pub fn parse<T: ParseQuote>(token_stream: TokenStream) -> T {
let parser = T::parse;
match parser.parse2(token_stream) {
Ok(t) => t,
Err(err) => panic!("{}", err),
}
}
#[doc(hidden)]
pub trait ParseQuote: Sized {
fn parse(input: ParseStream) -> Result<Self>;
}
impl<T: Parse> ParseQuote for T {
fn parse(input: ParseStream) -> Result<Self> {
<T as Parse>::parse(input)
}
}
////////////////////////////////////////////////////////////////////////////////
// Any other types that we want `parse_quote!` to be able to parse.
use crate::punctuated::Punctuated;
#[cfg(any(feature = "full", feature = "derive"))]
use crate::{attr, Attribute, Field, FieldMutability, Ident, Type, Visibility};
#[cfg(feature = "full")]
use crate::{Arm, Block, Pat, Stmt};
#[cfg(any(feature = "full", feature = "derive"))]
impl ParseQuote for Attribute {
fn parse(input: ParseStream) -> Result<Self> {
if input.peek(Token![#]) && input.peek2(Token![!]) {
attr::parsing::single_parse_inner(input)
} else {
attr::parsing::single_parse_outer(input)
}
}
}
#[cfg(any(feature = "full", feature = "derive"))]
impl ParseQuote for Vec<Attribute> {
fn parse(input: ParseStream) -> Result<Self> {
let mut attrs = Vec::new();
while !input.is_empty() {
attrs.push(ParseQuote::parse(input)?);
}
Ok(attrs)
}
}
#[cfg(any(feature = "full", feature = "derive"))]
impl ParseQuote for Field {
fn parse(input: ParseStream) -> Result<Self> {
let attrs = input.call(Attribute::parse_outer)?;
let vis: Visibility = input.parse()?;
let ident: Option<Ident>;
let colon_token: Option<Token![:]>;
let is_named = input.peek(Ident) && input.peek2(Token![:]) && !input.peek2(Token![::]);
if is_named {
ident = Some(input.parse()?);
colon_token = Some(input.parse()?);
} else {
ident = None;
colon_token = None;
}
let ty: Type = input.parse()?;
Ok(Field {
attrs,
vis,
mutability: FieldMutability::None,
ident,
colon_token,
ty,
})
}
}
#[cfg(feature = "full")]
impl ParseQuote for Pat {
fn parse(input: ParseStream) -> Result<Self> {
Pat::parse_multi_with_leading_vert(input)
}
}
#[cfg(feature = "full")]
impl ParseQuote for Box<Pat> {
fn parse(input: ParseStream) -> Result<Self> {
<Pat as ParseQuote>::parse(input).map(Box::new)
}
}
impl<T: Parse, P: Parse> ParseQuote for Punctuated<T, P> {
fn parse(input: ParseStream) -> Result<Self> {
Self::parse_terminated(input)
}
}
#[cfg(feature = "full")]
impl ParseQuote for Vec<Stmt> {
fn parse(input: ParseStream) -> Result<Self> {
Block::parse_within(input)
}
}
#[cfg(feature = "full")]
impl ParseQuote for Vec<Arm> {
fn parse(input: ParseStream) -> Result<Self> {
Arm::parse_multiple(input)
}
}

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use crate::attr::Attribute;
use crate::expr::Member;
use crate::ident::Ident;
use crate::path::{Path, QSelf};
use crate::punctuated::Punctuated;
use crate::token;
use crate::ty::Type;
use proc_macro2::TokenStream;
pub use crate::expr::{
ExprConst as PatConst, ExprLit as PatLit, ExprMacro as PatMacro, ExprPath as PatPath,
ExprRange as PatRange,
};
ast_enum_of_structs! {
/// A pattern in a local binding, function signature, match expression, or
/// various other places.
///
/// # Syntax tree enum
///
/// This type is a [syntax tree enum].
///
/// [syntax tree enum]: crate::expr::Expr#syntax-tree-enums
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
#[non_exhaustive]
pub enum Pat {
/// A const block: `const { ... }`.
Const(PatConst),
/// A pattern that binds a new variable: `ref mut binding @ SUBPATTERN`.
Ident(PatIdent),
/// A literal pattern: `0`.
Lit(PatLit),
/// A macro in pattern position.
Macro(PatMacro),
/// A pattern that matches any one of a set of cases.
Or(PatOr),
/// A parenthesized pattern: `(A | B)`.
Paren(PatParen),
/// A path pattern like `Color::Red`, optionally qualified with a
/// self-type.
///
/// Unqualified path patterns can legally refer to variants, structs,
/// constants or associated constants. Qualified path patterns like
/// `<A>::B::C` and `<A as Trait>::B::C` can only legally refer to
/// associated constants.
Path(PatPath),
/// A range pattern: `1..=2`.
Range(PatRange),
/// A reference pattern: `&mut var`.
Reference(PatReference),
/// The dots in a tuple or slice pattern: `[0, 1, ..]`.
Rest(PatRest),
/// A dynamically sized slice pattern: `[a, b, ref i @ .., y, z]`.
Slice(PatSlice),
/// A struct or struct variant pattern: `Variant { x, y, .. }`.
Struct(PatStruct),
/// A tuple pattern: `(a, b)`.
Tuple(PatTuple),
/// A tuple struct or tuple variant pattern: `Variant(x, y, .., z)`.
TupleStruct(PatTupleStruct),
/// A type ascription pattern: `foo: f64`.
Type(PatType),
/// Tokens in pattern position not interpreted by Syn.
Verbatim(TokenStream),
/// A pattern that matches any value: `_`.
Wild(PatWild),
// For testing exhaustiveness in downstream code, use the following idiom:
//
// match pat {
// #![cfg_attr(test, deny(non_exhaustive_omitted_patterns))]
//
// Pat::Box(pat) => {...}
// Pat::Ident(pat) => {...}
// ...
// Pat::Wild(pat) => {...}
//
// _ => { /* some sane fallback */ }
// }
//
// This way we fail your tests but don't break your library when adding
// a variant. You will be notified by a test failure when a variant is
// added, so that you can add code to handle it, but your library will
// continue to compile and work for downstream users in the interim.
}
}
ast_struct! {
/// A pattern that binds a new variable: `ref mut binding @ SUBPATTERN`.
///
/// It may also be a unit struct or struct variant (e.g. `None`), or a
/// constant; these cannot be distinguished syntactically.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct PatIdent {
pub attrs: Vec<Attribute>,
pub by_ref: Option<Token![ref]>,
pub mutability: Option<Token![mut]>,
pub ident: Ident,
pub subpat: Option<(Token![@], Box<Pat>)>,
}
}
ast_struct! {
/// A pattern that matches any one of a set of cases.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct PatOr {
pub attrs: Vec<Attribute>,
pub leading_vert: Option<Token![|]>,
pub cases: Punctuated<Pat, Token![|]>,
}
}
ast_struct! {
/// A parenthesized pattern: `(A | B)`.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct PatParen {
pub attrs: Vec<Attribute>,
pub paren_token: token::Paren,
pub pat: Box<Pat>,
}
}
ast_struct! {
/// A reference pattern: `&mut var`.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct PatReference {
pub attrs: Vec<Attribute>,
pub and_token: Token![&],
pub mutability: Option<Token![mut]>,
pub pat: Box<Pat>,
}
}
ast_struct! {
/// The dots in a tuple or slice pattern: `[0, 1, ..]`.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct PatRest {
pub attrs: Vec<Attribute>,
pub dot2_token: Token![..],
}
}
ast_struct! {
/// A dynamically sized slice pattern: `[a, b, ref i @ .., y, z]`.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct PatSlice {
pub attrs: Vec<Attribute>,
pub bracket_token: token::Bracket,
pub elems: Punctuated<Pat, Token![,]>,
}
}
ast_struct! {
/// A struct or struct variant pattern: `Variant { x, y, .. }`.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct PatStruct {
pub attrs: Vec<Attribute>,
pub qself: Option<QSelf>,
pub path: Path,
pub brace_token: token::Brace,
pub fields: Punctuated<FieldPat, Token![,]>,
pub rest: Option<PatRest>,
}
}
ast_struct! {
/// A tuple pattern: `(a, b)`.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct PatTuple {
pub attrs: Vec<Attribute>,
pub paren_token: token::Paren,
pub elems: Punctuated<Pat, Token![,]>,
}
}
ast_struct! {
/// A tuple struct or tuple variant pattern: `Variant(x, y, .., z)`.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct PatTupleStruct {
pub attrs: Vec<Attribute>,
pub qself: Option<QSelf>,
pub path: Path,
pub paren_token: token::Paren,
pub elems: Punctuated<Pat, Token![,]>,
}
}
ast_struct! {
/// A type ascription pattern: `foo: f64`.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct PatType {
pub attrs: Vec<Attribute>,
pub pat: Box<Pat>,
pub colon_token: Token![:],
pub ty: Box<Type>,
}
}
ast_struct! {
/// A pattern that matches any value: `_`.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct PatWild {
pub attrs: Vec<Attribute>,
pub underscore_token: Token![_],
}
}
ast_struct! {
/// A single field in a struct pattern.
///
/// Patterns like the fields of Foo `{ x, ref y, ref mut z }` are treated
/// the same as `x: x, y: ref y, z: ref mut z` but there is no colon token.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct FieldPat {
pub attrs: Vec<Attribute>,
pub member: Member,
pub colon_token: Option<Token![:]>,
pub pat: Box<Pat>,
}
}
#[cfg(feature = "parsing")]
pub(crate) mod parsing {
use crate::attr::Attribute;
use crate::error::{self, Result};
use crate::expr::{
Expr, ExprConst, ExprLit, ExprMacro, ExprPath, ExprRange, Member, RangeLimits,
};
use crate::ext::IdentExt as _;
use crate::ident::Ident;
use crate::lit::Lit;
use crate::mac::{self, Macro};
use crate::parse::{Parse, ParseBuffer, ParseStream};
use crate::pat::{
FieldPat, Pat, PatIdent, PatOr, PatParen, PatReference, PatRest, PatSlice, PatStruct,
PatTuple, PatTupleStruct, PatType, PatWild,
};
use crate::path::{self, Path, QSelf};
use crate::punctuated::Punctuated;
use crate::stmt::Block;
use crate::token;
use crate::verbatim;
use proc_macro2::TokenStream;
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Pat {
/// Parse a pattern that does _not_ involve `|` at the top level.
///
/// This parser matches the behavior of the `$:pat_param` macro_rules
/// matcher, and on editions prior to Rust 2021, the behavior of
/// `$:pat`.
///
/// In Rust syntax, some examples of where this syntax would occur are
/// in the argument pattern of functions and closures. Patterns using
/// `|` are not allowed to occur in these positions.
///
/// ```compile_fail
/// fn f(Some(_) | None: Option<T>) {
/// let _ = |Some(_) | None: Option<T>| {};
/// // ^^^^^^^^^^^^^^^^^^^^^^^^^??? :(
/// }
/// ```
///
/// ```console
/// error: top-level or-patterns are not allowed in function parameters
/// --> src/main.rs:1:6
/// |
/// 1 | fn f(Some(_) | None: Option<T>) {
/// | ^^^^^^^^^^^^^^ help: wrap the pattern in parentheses: `(Some(_) | None)`
/// ```
pub fn parse_single(input: ParseStream) -> Result<Self> {
let begin = input.fork();
let lookahead = input.lookahead1();
if lookahead.peek(Ident)
&& (input.peek2(Token![::])
|| input.peek2(Token![!])
|| input.peek2(token::Brace)
|| input.peek2(token::Paren)
|| input.peek2(Token![..]))
|| input.peek(Token![self]) && input.peek2(Token![::])
|| lookahead.peek(Token![::])
|| lookahead.peek(Token![<])
|| input.peek(Token![Self])
|| input.peek(Token![super])
|| input.peek(Token![crate])
{
pat_path_or_macro_or_struct_or_range(input)
} else if lookahead.peek(Token![_]) {
input.call(pat_wild).map(Pat::Wild)
} else if input.peek(Token![box]) {
pat_box(begin, input)
} else if input.peek(Token![-]) || lookahead.peek(Lit) || lookahead.peek(Token![const])
{
pat_lit_or_range(input)
} else if lookahead.peek(Token![ref])
|| lookahead.peek(Token![mut])
|| input.peek(Token![self])
|| input.peek(Ident)
{
input.call(pat_ident).map(Pat::Ident)
} else if lookahead.peek(Token![&]) {
input.call(pat_reference).map(Pat::Reference)
} else if lookahead.peek(token::Paren) {
input.call(pat_paren_or_tuple)
} else if lookahead.peek(token::Bracket) {
input.call(pat_slice).map(Pat::Slice)
} else if lookahead.peek(Token![..]) && !input.peek(Token![...]) {
pat_range_half_open(input)
} else if lookahead.peek(Token![const]) {
input.call(pat_const).map(Pat::Verbatim)
} else {
Err(lookahead.error())
}
}
/// Parse a pattern, possibly involving `|`, but not a leading `|`.
pub fn parse_multi(input: ParseStream) -> Result<Self> {
multi_pat_impl(input, None)
}
/// Parse a pattern, possibly involving `|`, possibly including a
/// leading `|`.
///
/// This parser matches the behavior of the Rust 2021 edition's `$:pat`
/// macro_rules matcher.
///
/// In Rust syntax, an example of where this syntax would occur is in
/// the pattern of a `match` arm, where the language permits an optional
/// leading `|`, although it is not idiomatic to write one there in
/// handwritten code.
///
/// ```
/// # let wat = None;
/// match wat {
/// | None | Some(false) => {}
/// | Some(true) => {}
/// }
/// ```
///
/// The compiler accepts it only to facilitate some situations in
/// macro-generated code where a macro author might need to write:
///
/// ```
/// # macro_rules! doc {
/// # ($value:expr, ($($conditions1:pat),*), ($($conditions2:pat),*), $then:expr) => {
/// match $value {
/// $(| $conditions1)* $(| $conditions2)* => $then
/// }
/// # };
/// # }
/// #
/// # doc!(true, (true), (false), {});
/// # doc!(true, (), (true, false), {});
/// # doc!(true, (true, false), (), {});
/// ```
///
/// Expressing the same thing correctly in the case that either one (but
/// not both) of `$conditions1` and `$conditions2` might be empty,
/// without leading `|`, is complex.
///
/// Use [`Pat::parse_multi`] instead if you are not intending to support
/// macro-generated macro input.
pub fn parse_multi_with_leading_vert(input: ParseStream) -> Result<Self> {
let leading_vert: Option<Token![|]> = input.parse()?;
multi_pat_impl(input, leading_vert)
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for PatType {
fn parse(input: ParseStream) -> Result<Self> {
Ok(PatType {
attrs: Vec::new(),
pat: Box::new(Pat::parse_single(input)?),
colon_token: input.parse()?,
ty: input.parse()?,
})
}
}
fn multi_pat_impl(input: ParseStream, leading_vert: Option<Token![|]>) -> Result<Pat> {
let mut pat = Pat::parse_single(input)?;
if leading_vert.is_some()
|| input.peek(Token![|]) && !input.peek(Token![||]) && !input.peek(Token![|=])
{
let mut cases = Punctuated::new();
cases.push_value(pat);
while input.peek(Token![|]) && !input.peek(Token![||]) && !input.peek(Token![|=]) {
let punct = input.parse()?;
cases.push_punct(punct);
let pat = Pat::parse_single(input)?;
cases.push_value(pat);
}
pat = Pat::Or(PatOr {
attrs: Vec::new(),
leading_vert,
cases,
});
}
Ok(pat)
}
fn pat_path_or_macro_or_struct_or_range(input: ParseStream) -> Result<Pat> {
let expr_style = true;
let (qself, path) = path::parsing::qpath(input, expr_style)?;
if qself.is_none()
&& input.peek(Token![!])
&& !input.peek(Token![!=])
&& path.is_mod_style()
{
let bang_token: Token![!] = input.parse()?;
let (delimiter, tokens) = mac::parse_delimiter(input)?;
return Ok(Pat::Macro(ExprMacro {
attrs: Vec::new(),
mac: Macro {
path,
bang_token,
delimiter,
tokens,
},
}));
}
if input.peek(token::Brace) {
pat_struct(input, qself, path).map(Pat::Struct)
} else if input.peek(token::Paren) {
pat_tuple_struct(input, qself, path).map(Pat::TupleStruct)
} else if input.peek(Token![..]) {
pat_range(input, qself, path)
} else {
Ok(Pat::Path(ExprPath {
attrs: Vec::new(),
qself,
path,
}))
}
}
fn pat_wild(input: ParseStream) -> Result<PatWild> {
Ok(PatWild {
attrs: Vec::new(),
underscore_token: input.parse()?,
})
}
fn pat_box(begin: ParseBuffer, input: ParseStream) -> Result<Pat> {
input.parse::<Token![box]>()?;
Pat::parse_single(input)?;
Ok(Pat::Verbatim(verbatim::between(&begin, input)))
}
fn pat_ident(input: ParseStream) -> Result<PatIdent> {
Ok(PatIdent {
attrs: Vec::new(),
by_ref: input.parse()?,
mutability: input.parse()?,
ident: {
if input.peek(Token![self]) {
input.call(Ident::parse_any)?
} else {
input.parse()?
}
},
subpat: {
if input.peek(Token![@]) {
let at_token: Token![@] = input.parse()?;
let subpat = Pat::parse_single(input)?;
Some((at_token, Box::new(subpat)))
} else {
None
}
},
})
}
fn pat_tuple_struct(
input: ParseStream,
qself: Option<QSelf>,
path: Path,
) -> Result<PatTupleStruct> {
let content;
let paren_token = parenthesized!(content in input);
let mut elems = Punctuated::new();
while !content.is_empty() {
let value = Pat::parse_multi_with_leading_vert(&content)?;
elems.push_value(value);
if content.is_empty() {
break;
}
let punct = content.parse()?;
elems.push_punct(punct);
}
Ok(PatTupleStruct {
attrs: Vec::new(),
qself,
path,
paren_token,
elems,
})
}
fn pat_struct(input: ParseStream, qself: Option<QSelf>, path: Path) -> Result<PatStruct> {
let content;
let brace_token = braced!(content in input);
let mut fields = Punctuated::new();
let mut rest = None;
while !content.is_empty() {
let attrs = content.call(Attribute::parse_outer)?;
if content.peek(Token![..]) {
rest = Some(PatRest {
attrs,
dot2_token: content.parse()?,
});
break;
}
let mut value = content.call(field_pat)?;
value.attrs = attrs;
fields.push_value(value);
if content.is_empty() {
break;
}
let punct: Token![,] = content.parse()?;
fields.push_punct(punct);
}
Ok(PatStruct {
attrs: Vec::new(),
qself,
path,
brace_token,
fields,
rest,
})
}
fn field_pat(input: ParseStream) -> Result<FieldPat> {
let begin = input.fork();
let boxed: Option<Token![box]> = input.parse()?;
let by_ref: Option<Token![ref]> = input.parse()?;
let mutability: Option<Token![mut]> = input.parse()?;
let member = if boxed.is_some() || by_ref.is_some() || mutability.is_some() {
input.parse().map(Member::Named)
} else {
input.parse()
}?;
if boxed.is_none() && by_ref.is_none() && mutability.is_none() && input.peek(Token![:])
|| !member.is_named()
{
return Ok(FieldPat {
attrs: Vec::new(),
member,
colon_token: Some(input.parse()?),
pat: Box::new(Pat::parse_multi_with_leading_vert(input)?),
});
}
let ident = match member {
Member::Named(ident) => ident,
Member::Unnamed(_) => unreachable!(),
};
let pat = if boxed.is_some() {
Pat::Verbatim(verbatim::between(&begin, input))
} else {
Pat::Ident(PatIdent {
attrs: Vec::new(),
by_ref,
mutability,
ident: ident.clone(),
subpat: None,
})
};
Ok(FieldPat {
attrs: Vec::new(),
member: Member::Named(ident),
colon_token: None,
pat: Box::new(pat),
})
}
fn pat_range(input: ParseStream, qself: Option<QSelf>, path: Path) -> Result<Pat> {
let limits = RangeLimits::parse_obsolete(input)?;
let end = input.call(pat_range_bound)?;
if let (RangeLimits::Closed(_), None) = (&limits, &end) {
return Err(input.error("expected range upper bound"));
}
Ok(Pat::Range(ExprRange {
attrs: Vec::new(),
start: Some(Box::new(Expr::Path(ExprPath {
attrs: Vec::new(),
qself,
path,
}))),
limits,
end: end.map(PatRangeBound::into_expr),
}))
}
fn pat_range_half_open(input: ParseStream) -> Result<Pat> {
let limits: RangeLimits = input.parse()?;
let end = input.call(pat_range_bound)?;
if end.is_some() {
Ok(Pat::Range(ExprRange {
attrs: Vec::new(),
start: None,
limits,
end: end.map(PatRangeBound::into_expr),
}))
} else {
match limits {
RangeLimits::HalfOpen(dot2_token) => Ok(Pat::Rest(PatRest {
attrs: Vec::new(),
dot2_token,
})),
RangeLimits::Closed(_) => Err(input.error("expected range upper bound")),
}
}
}
fn pat_paren_or_tuple(input: ParseStream) -> Result<Pat> {
let content;
let paren_token = parenthesized!(content in input);
let mut elems = Punctuated::new();
while !content.is_empty() {
let value = Pat::parse_multi_with_leading_vert(&content)?;
if content.is_empty() {
if elems.is_empty() && !matches!(value, Pat::Rest(_)) {
return Ok(Pat::Paren(PatParen {
attrs: Vec::new(),
paren_token,
pat: Box::new(value),
}));
}
elems.push_value(value);
break;
}
elems.push_value(value);
let punct = content.parse()?;
elems.push_punct(punct);
}
Ok(Pat::Tuple(PatTuple {
attrs: Vec::new(),
paren_token,
elems,
}))
}
fn pat_reference(input: ParseStream) -> Result<PatReference> {
Ok(PatReference {
attrs: Vec::new(),
and_token: input.parse()?,
mutability: input.parse()?,
pat: Box::new(Pat::parse_single(input)?),
})
}
fn pat_lit_or_range(input: ParseStream) -> Result<Pat> {
let start = input.call(pat_range_bound)?.unwrap();
if input.peek(Token![..]) {
let limits = RangeLimits::parse_obsolete(input)?;
let end = input.call(pat_range_bound)?;
if let (RangeLimits::Closed(_), None) = (&limits, &end) {
return Err(input.error("expected range upper bound"));
}
Ok(Pat::Range(ExprRange {
attrs: Vec::new(),
start: Some(start.into_expr()),
limits,
end: end.map(PatRangeBound::into_expr),
}))
} else {
Ok(start.into_pat())
}
}
// Patterns that can appear on either side of a range pattern.
enum PatRangeBound {
Const(ExprConst),
Lit(ExprLit),
Path(ExprPath),
}
impl PatRangeBound {
fn into_expr(self) -> Box<Expr> {
Box::new(match self {
PatRangeBound::Const(pat) => Expr::Const(pat),
PatRangeBound::Lit(pat) => Expr::Lit(pat),
PatRangeBound::Path(pat) => Expr::Path(pat),
})
}
fn into_pat(self) -> Pat {
match self {
PatRangeBound::Const(pat) => Pat::Const(pat),
PatRangeBound::Lit(pat) => Pat::Lit(pat),
PatRangeBound::Path(pat) => Pat::Path(pat),
}
}
}
fn pat_range_bound(input: ParseStream) -> Result<Option<PatRangeBound>> {
if input.is_empty()
|| input.peek(Token![|])
|| input.peek(Token![=])
|| input.peek(Token![:]) && !input.peek(Token![::])
|| input.peek(Token![,])
|| input.peek(Token![;])
|| input.peek(Token![if])
{
return Ok(None);
}
let lookahead = input.lookahead1();
let expr = if lookahead.peek(Lit) {
PatRangeBound::Lit(input.parse()?)
} else if lookahead.peek(Ident)
|| lookahead.peek(Token![::])
|| lookahead.peek(Token![<])
|| lookahead.peek(Token![self])
|| lookahead.peek(Token![Self])
|| lookahead.peek(Token![super])
|| lookahead.peek(Token![crate])
{
PatRangeBound::Path(input.parse()?)
} else if lookahead.peek(Token![const]) {
PatRangeBound::Const(input.parse()?)
} else {
return Err(lookahead.error());
};
Ok(Some(expr))
}
fn pat_slice(input: ParseStream) -> Result<PatSlice> {
let content;
let bracket_token = bracketed!(content in input);
let mut elems = Punctuated::new();
while !content.is_empty() {
let value = Pat::parse_multi_with_leading_vert(&content)?;
match value {
Pat::Range(pat) if pat.start.is_none() || pat.end.is_none() => {
let (start, end) = match pat.limits {
RangeLimits::HalfOpen(dot_dot) => (dot_dot.spans[0], dot_dot.spans[1]),
RangeLimits::Closed(dot_dot_eq) => {
(dot_dot_eq.spans[0], dot_dot_eq.spans[2])
}
};
let msg = "range pattern is not allowed unparenthesized inside slice pattern";
return Err(error::new2(start, end, msg));
}
_ => {}
}
elems.push_value(value);
if content.is_empty() {
break;
}
let punct = content.parse()?;
elems.push_punct(punct);
}
Ok(PatSlice {
attrs: Vec::new(),
bracket_token,
elems,
})
}
fn pat_const(input: ParseStream) -> Result<TokenStream> {
let begin = input.fork();
input.parse::<Token![const]>()?;
let content;
braced!(content in input);
content.call(Attribute::parse_inner)?;
content.call(Block::parse_within)?;
Ok(verbatim::between(&begin, input))
}
}
#[cfg(feature = "printing")]
mod printing {
use crate::attr::FilterAttrs;
use crate::pat::{
FieldPat, Pat, PatIdent, PatOr, PatParen, PatReference, PatRest, PatSlice, PatStruct,
PatTuple, PatTupleStruct, PatType, PatWild,
};
use crate::path;
use crate::path::printing::PathStyle;
use proc_macro2::TokenStream;
use quote::{ToTokens, TokenStreamExt};
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for PatIdent {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.append_all(self.attrs.outer());
self.by_ref.to_tokens(tokens);
self.mutability.to_tokens(tokens);
self.ident.to_tokens(tokens);
if let Some((at_token, subpat)) = &self.subpat {
at_token.to_tokens(tokens);
subpat.to_tokens(tokens);
}
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for PatOr {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.append_all(self.attrs.outer());
self.leading_vert.to_tokens(tokens);
self.cases.to_tokens(tokens);
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for PatParen {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.append_all(self.attrs.outer());
self.paren_token.surround(tokens, |tokens| {
self.pat.to_tokens(tokens);
});
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for PatReference {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.append_all(self.attrs.outer());
self.and_token.to_tokens(tokens);
self.mutability.to_tokens(tokens);
self.pat.to_tokens(tokens);
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for PatRest {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.append_all(self.attrs.outer());
self.dot2_token.to_tokens(tokens);
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for PatSlice {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.append_all(self.attrs.outer());
self.bracket_token.surround(tokens, |tokens| {
self.elems.to_tokens(tokens);
});
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for PatStruct {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.append_all(self.attrs.outer());
path::printing::print_qpath(tokens, &self.qself, &self.path, PathStyle::Expr);
self.brace_token.surround(tokens, |tokens| {
self.fields.to_tokens(tokens);
// NOTE: We need a comma before the dot2 token if it is present.
if !self.fields.empty_or_trailing() && self.rest.is_some() {
<Token![,]>::default().to_tokens(tokens);
}
self.rest.to_tokens(tokens);
});
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for PatTuple {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.append_all(self.attrs.outer());
self.paren_token.surround(tokens, |tokens| {
self.elems.to_tokens(tokens);
// If there is only one element, a trailing comma is needed to
// distinguish PatTuple from PatParen, unless this is `(..)`
// which is a tuple pattern even without comma.
if self.elems.len() == 1
&& !self.elems.trailing_punct()
&& !matches!(self.elems[0], Pat::Rest { .. })
{
<Token![,]>::default().to_tokens(tokens);
}
});
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for PatTupleStruct {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.append_all(self.attrs.outer());
path::printing::print_qpath(tokens, &self.qself, &self.path, PathStyle::Expr);
self.paren_token.surround(tokens, |tokens| {
self.elems.to_tokens(tokens);
});
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for PatType {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.append_all(self.attrs.outer());
self.pat.to_tokens(tokens);
self.colon_token.to_tokens(tokens);
self.ty.to_tokens(tokens);
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for PatWild {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.append_all(self.attrs.outer());
self.underscore_token.to_tokens(tokens);
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for FieldPat {
fn to_tokens(&self, tokens: &mut TokenStream) {
tokens.append_all(self.attrs.outer());
if let Some(colon_token) = &self.colon_token {
self.member.to_tokens(tokens);
colon_token.to_tokens(tokens);
}
self.pat.to_tokens(tokens);
}
}
}

966
rust/syn/path.rs Normal file
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@@ -0,0 +1,966 @@
#[cfg(feature = "parsing")]
use crate::error::Result;
use crate::expr::Expr;
use crate::generics::TypeParamBound;
use crate::ident::Ident;
use crate::lifetime::Lifetime;
use crate::punctuated::Punctuated;
use crate::token;
use crate::ty::{ReturnType, Type};
ast_struct! {
/// A path at which a named item is exported (e.g. `std::collections::HashMap`).
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct Path {
pub leading_colon: Option<Token![::]>,
pub segments: Punctuated<PathSegment, Token![::]>,
}
}
impl<T> From<T> for Path
where
T: Into<PathSegment>,
{
fn from(segment: T) -> Self {
let mut path = Path {
leading_colon: None,
segments: Punctuated::new(),
};
path.segments.push_value(segment.into());
path
}
}
impl Path {
/// Determines whether this is a path of length 1 equal to the given
/// ident.
///
/// For them to compare equal, it must be the case that:
///
/// - the path has no leading colon,
/// - the number of path segments is 1,
/// - the first path segment has no angle bracketed or parenthesized
/// path arguments, and
/// - the ident of the first path segment is equal to the given one.
///
/// # Example
///
/// ```
/// use proc_macro2::TokenStream;
/// use syn::{Attribute, Error, Meta, Result};
///
/// fn get_serde_meta_item(attr: &Attribute) -> Result<Option<&TokenStream>> {
/// if attr.path().is_ident("serde") {
/// match &attr.meta {
/// Meta::List(meta) => Ok(Some(&meta.tokens)),
/// bad => Err(Error::new_spanned(bad, "unrecognized attribute")),
/// }
/// } else {
/// Ok(None)
/// }
/// }
/// ```
pub fn is_ident<I>(&self, ident: &I) -> bool
where
I: ?Sized,
Ident: PartialEq<I>,
{
match self.get_ident() {
Some(id) => id == ident,
None => false,
}
}
/// If this path consists of a single ident, returns the ident.
///
/// A path is considered an ident if:
///
/// - the path has no leading colon,
/// - the number of path segments is 1, and
/// - the first path segment has no angle bracketed or parenthesized
/// path arguments.
pub fn get_ident(&self) -> Option<&Ident> {
if self.leading_colon.is_none()
&& self.segments.len() == 1
&& self.segments[0].arguments.is_none()
{
Some(&self.segments[0].ident)
} else {
None
}
}
/// An error if this path is not a single ident, as defined in `get_ident`.
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn require_ident(&self) -> Result<&Ident> {
self.get_ident().ok_or_else(|| {
crate::error::new2(
self.segments.first().unwrap().ident.span(),
self.segments.last().unwrap().ident.span(),
"expected this path to be an identifier",
)
})
}
}
ast_struct! {
/// A segment of a path together with any path arguments on that segment.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct PathSegment {
pub ident: Ident,
pub arguments: PathArguments,
}
}
impl<T> From<T> for PathSegment
where
T: Into<Ident>,
{
fn from(ident: T) -> Self {
PathSegment {
ident: ident.into(),
arguments: PathArguments::None,
}
}
}
ast_enum! {
/// Angle bracketed or parenthesized arguments of a path segment.
///
/// ## Angle bracketed
///
/// The `<'a, T>` in `std::slice::iter<'a, T>`.
///
/// ## Parenthesized
///
/// The `(A, B) -> C` in `Fn(A, B) -> C`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub enum PathArguments {
None,
/// The `<'a, T>` in `std::slice::iter<'a, T>`.
AngleBracketed(AngleBracketedGenericArguments),
/// The `(A, B) -> C` in `Fn(A, B) -> C`.
Parenthesized(ParenthesizedGenericArguments),
}
}
impl Default for PathArguments {
fn default() -> Self {
PathArguments::None
}
}
impl PathArguments {
pub fn is_empty(&self) -> bool {
match self {
PathArguments::None => true,
PathArguments::AngleBracketed(bracketed) => bracketed.args.is_empty(),
PathArguments::Parenthesized(_) => false,
}
}
pub fn is_none(&self) -> bool {
match self {
PathArguments::None => true,
PathArguments::AngleBracketed(_) | PathArguments::Parenthesized(_) => false,
}
}
}
ast_enum! {
/// An individual generic argument, like `'a`, `T`, or `Item = T`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
#[non_exhaustive]
pub enum GenericArgument {
/// A lifetime argument.
Lifetime(Lifetime),
/// A type argument.
Type(Type),
/// A const expression. Must be inside of a block.
///
/// NOTE: Identity expressions are represented as Type arguments, as
/// they are indistinguishable syntactically.
Const(Expr),
/// A binding (equality constraint) on an associated type: the `Item =
/// u8` in `Iterator<Item = u8>`.
AssocType(AssocType),
/// An equality constraint on an associated constant: the `PANIC =
/// false` in `Trait<PANIC = false>`.
AssocConst(AssocConst),
/// An associated type bound: `Iterator<Item: Display>`.
Constraint(Constraint),
}
}
ast_struct! {
/// Angle bracketed arguments of a path segment: the `<K, V>` in `HashMap<K,
/// V>`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct AngleBracketedGenericArguments {
pub colon2_token: Option<Token![::]>,
pub lt_token: Token![<],
pub args: Punctuated<GenericArgument, Token![,]>,
pub gt_token: Token![>],
}
}
ast_struct! {
/// A binding (equality constraint) on an associated type: the `Item = u8`
/// in `Iterator<Item = u8>`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct AssocType {
pub ident: Ident,
pub generics: Option<AngleBracketedGenericArguments>,
pub eq_token: Token![=],
pub ty: Type,
}
}
ast_struct! {
/// An equality constraint on an associated constant: the `PANIC = false` in
/// `Trait<PANIC = false>`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct AssocConst {
pub ident: Ident,
pub generics: Option<AngleBracketedGenericArguments>,
pub eq_token: Token![=],
pub value: Expr,
}
}
ast_struct! {
/// An associated type bound: `Iterator<Item: Display>`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct Constraint {
pub ident: Ident,
pub generics: Option<AngleBracketedGenericArguments>,
pub colon_token: Token![:],
pub bounds: Punctuated<TypeParamBound, Token![+]>,
}
}
ast_struct! {
/// Arguments of a function path segment: the `(A, B) -> C` in `Fn(A,B) ->
/// C`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct ParenthesizedGenericArguments {
pub paren_token: token::Paren,
/// `(A, B)`
pub inputs: Punctuated<Type, Token![,]>,
/// `C`
pub output: ReturnType,
}
}
ast_struct! {
/// The explicit Self type in a qualified path: the `T` in `<T as
/// Display>::fmt`.
///
/// The actual path, including the trait and the associated item, is stored
/// separately. The `position` field represents the index of the associated
/// item qualified with this Self type.
///
/// ```text
/// <Vec<T> as a::b::Trait>::AssociatedItem
/// ^~~~~~ ~~~~~~~~~~~~~~^
/// ty position = 3
///
/// <Vec<T>>::AssociatedItem
/// ^~~~~~ ^
/// ty position = 0
/// ```
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct QSelf {
pub lt_token: Token![<],
pub ty: Box<Type>,
pub position: usize,
pub as_token: Option<Token![as]>,
pub gt_token: Token![>],
}
}
#[cfg(feature = "parsing")]
pub(crate) mod parsing {
use crate::error::Result;
#[cfg(feature = "full")]
use crate::expr::ExprBlock;
use crate::expr::{Expr, ExprPath};
use crate::ext::IdentExt as _;
#[cfg(feature = "full")]
use crate::generics::TypeParamBound;
use crate::ident::Ident;
use crate::lifetime::Lifetime;
use crate::lit::Lit;
use crate::parse::{Parse, ParseStream};
#[cfg(feature = "full")]
use crate::path::Constraint;
use crate::path::{
AngleBracketedGenericArguments, AssocConst, AssocType, GenericArgument,
ParenthesizedGenericArguments, Path, PathArguments, PathSegment, QSelf,
};
use crate::punctuated::Punctuated;
use crate::token;
use crate::ty::{ReturnType, Type};
#[cfg(not(feature = "full"))]
use crate::verbatim;
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for Path {
fn parse(input: ParseStream) -> Result<Self> {
Self::parse_helper(input, false)
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for GenericArgument {
fn parse(input: ParseStream) -> Result<Self> {
if input.peek(Lifetime) && !input.peek2(Token![+]) {
return Ok(GenericArgument::Lifetime(input.parse()?));
}
if input.peek(Lit) || input.peek(token::Brace) {
return const_argument(input).map(GenericArgument::Const);
}
let mut argument: Type = input.parse()?;
match argument {
Type::Path(mut ty)
if ty.qself.is_none()
&& ty.path.leading_colon.is_none()
&& ty.path.segments.len() == 1
&& match &ty.path.segments[0].arguments {
PathArguments::None | PathArguments::AngleBracketed(_) => true,
PathArguments::Parenthesized(_) => false,
} =>
{
if let Some(eq_token) = input.parse::<Option<Token![=]>>()? {
let segment = ty.path.segments.pop().unwrap().into_value();
let ident = segment.ident;
let generics = match segment.arguments {
PathArguments::None => None,
PathArguments::AngleBracketed(arguments) => Some(arguments),
PathArguments::Parenthesized(_) => unreachable!(),
};
return if input.peek(Lit) || input.peek(token::Brace) {
Ok(GenericArgument::AssocConst(AssocConst {
ident,
generics,
eq_token,
value: const_argument(input)?,
}))
} else {
Ok(GenericArgument::AssocType(AssocType {
ident,
generics,
eq_token,
ty: input.parse()?,
}))
};
}
#[cfg(feature = "full")]
if let Some(colon_token) = input.parse::<Option<Token![:]>>()? {
let segment = ty.path.segments.pop().unwrap().into_value();
return Ok(GenericArgument::Constraint(Constraint {
ident: segment.ident,
generics: match segment.arguments {
PathArguments::None => None,
PathArguments::AngleBracketed(arguments) => Some(arguments),
PathArguments::Parenthesized(_) => unreachable!(),
},
colon_token,
bounds: {
let mut bounds = Punctuated::new();
loop {
if input.peek(Token![,]) || input.peek(Token![>]) {
break;
}
bounds.push_value({
let allow_precise_capture = false;
let allow_const = true;
TypeParamBound::parse_single(
input,
allow_precise_capture,
allow_const,
)?
});
if !input.peek(Token![+]) {
break;
}
let punct: Token![+] = input.parse()?;
bounds.push_punct(punct);
}
bounds
},
}));
}
argument = Type::Path(ty);
}
_ => {}
}
Ok(GenericArgument::Type(argument))
}
}
pub(crate) fn const_argument(input: ParseStream) -> Result<Expr> {
let lookahead = input.lookahead1();
if input.peek(Lit) {
let lit = input.parse()?;
return Ok(Expr::Lit(lit));
}
if input.peek(Ident) {
let ident: Ident = input.parse()?;
return Ok(Expr::Path(ExprPath {
attrs: Vec::new(),
qself: None,
path: Path::from(ident),
}));
}
if input.peek(token::Brace) {
#[cfg(feature = "full")]
{
let block: ExprBlock = input.parse()?;
return Ok(Expr::Block(block));
}
#[cfg(not(feature = "full"))]
{
let begin = input.fork();
let content;
braced!(content in input);
content.parse::<Expr>()?;
let verbatim = verbatim::between(&begin, input);
return Ok(Expr::Verbatim(verbatim));
}
}
Err(lookahead.error())
}
impl AngleBracketedGenericArguments {
/// Parse `::<…>` with mandatory leading `::`.
///
/// The ordinary [`Parse`] impl for `AngleBracketedGenericArguments`
/// parses optional leading `::`.
#[cfg(feature = "full")]
#[cfg_attr(docsrs, doc(cfg(all(feature = "parsing", feature = "full"))))]
pub fn parse_turbofish(input: ParseStream) -> Result<Self> {
let colon2_token: Token![::] = input.parse()?;
Self::do_parse(Some(colon2_token), input)
}
pub(crate) fn do_parse(
colon2_token: Option<Token![::]>,
input: ParseStream,
) -> Result<Self> {
Ok(AngleBracketedGenericArguments {
colon2_token,
lt_token: input.parse()?,
args: {
let mut args = Punctuated::new();
loop {
if input.peek(Token![>]) {
break;
}
let value: GenericArgument = input.parse()?;
args.push_value(value);
if input.peek(Token![>]) {
break;
}
let punct: Token![,] = input.parse()?;
args.push_punct(punct);
}
args
},
gt_token: input.parse()?,
})
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for AngleBracketedGenericArguments {
fn parse(input: ParseStream) -> Result<Self> {
let colon2_token: Option<Token![::]> = input.parse()?;
Self::do_parse(colon2_token, input)
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for ParenthesizedGenericArguments {
fn parse(input: ParseStream) -> Result<Self> {
let content;
Ok(ParenthesizedGenericArguments {
paren_token: parenthesized!(content in input),
inputs: content.parse_terminated(Type::parse, Token![,])?,
output: input.call(ReturnType::without_plus)?,
})
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for PathSegment {
fn parse(input: ParseStream) -> Result<Self> {
Self::parse_helper(input, false)
}
}
impl PathSegment {
fn parse_helper(input: ParseStream, expr_style: bool) -> Result<Self> {
if input.peek(Token![super])
|| input.peek(Token![self])
|| input.peek(Token![crate])
|| cfg!(feature = "full") && input.peek(Token![try])
{
let ident = input.call(Ident::parse_any)?;
return Ok(PathSegment::from(ident));
}
let ident = if input.peek(Token![Self]) {
input.call(Ident::parse_any)?
} else {
input.parse()?
};
if !expr_style
&& input.peek(Token![<])
&& !input.peek(Token![<=])
&& !input.peek(Token![<<=])
|| input.peek(Token![::]) && input.peek3(Token![<])
{
Ok(PathSegment {
ident,
arguments: PathArguments::AngleBracketed(input.parse()?),
})
} else {
Ok(PathSegment::from(ident))
}
}
}
impl Path {
/// Parse a `Path` containing no path arguments on any of its segments.
///
/// # Example
///
/// ```
/// use syn::{Path, Result, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // A simplified single `use` statement like:
/// //
/// // use std::collections::HashMap;
/// //
/// // Note that generic parameters are not allowed in a `use` statement
/// // so the following must not be accepted.
/// //
/// // use a::<b>::c;
/// struct SingleUse {
/// use_token: Token![use],
/// path: Path,
/// }
///
/// impl Parse for SingleUse {
/// fn parse(input: ParseStream) -> Result<Self> {
/// Ok(SingleUse {
/// use_token: input.parse()?,
/// path: input.call(Path::parse_mod_style)?,
/// })
/// }
/// }
/// ```
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_mod_style(input: ParseStream) -> Result<Self> {
Ok(Path {
leading_colon: input.parse()?,
segments: {
let mut segments = Punctuated::new();
loop {
if !input.peek(Ident)
&& !input.peek(Token![super])
&& !input.peek(Token![self])
&& !input.peek(Token![Self])
&& !input.peek(Token![crate])
{
break;
}
let ident = Ident::parse_any(input)?;
segments.push_value(PathSegment::from(ident));
if !input.peek(Token![::]) {
break;
}
let punct = input.parse()?;
segments.push_punct(punct);
}
if segments.is_empty() {
return Err(input.parse::<Ident>().unwrap_err());
} else if segments.trailing_punct() {
return Err(input.error("expected path segment after `::`"));
}
segments
},
})
}
pub(crate) fn parse_helper(input: ParseStream, expr_style: bool) -> Result<Self> {
let mut path = Path {
leading_colon: input.parse()?,
segments: {
let mut segments = Punctuated::new();
let value = PathSegment::parse_helper(input, expr_style)?;
segments.push_value(value);
segments
},
};
Path::parse_rest(input, &mut path, expr_style)?;
Ok(path)
}
pub(crate) fn parse_rest(
input: ParseStream,
path: &mut Self,
expr_style: bool,
) -> Result<()> {
while input.peek(Token![::]) && !input.peek3(token::Paren) {
let punct: Token![::] = input.parse()?;
path.segments.push_punct(punct);
let value = PathSegment::parse_helper(input, expr_style)?;
path.segments.push_value(value);
}
Ok(())
}
pub(crate) fn is_mod_style(&self) -> bool {
self.segments
.iter()
.all(|segment| segment.arguments.is_none())
}
}
pub(crate) fn qpath(input: ParseStream, expr_style: bool) -> Result<(Option<QSelf>, Path)> {
if input.peek(Token![<]) {
let lt_token: Token![<] = input.parse()?;
let this: Type = input.parse()?;
let path = if input.peek(Token![as]) {
let as_token: Token![as] = input.parse()?;
let path: Path = input.parse()?;
Some((as_token, path))
} else {
None
};
let gt_token: Token![>] = input.parse()?;
let colon2_token: Token![::] = input.parse()?;
let mut rest = Punctuated::new();
loop {
let path = PathSegment::parse_helper(input, expr_style)?;
rest.push_value(path);
if !input.peek(Token![::]) {
break;
}
let punct: Token![::] = input.parse()?;
rest.push_punct(punct);
}
let (position, as_token, path) = match path {
Some((as_token, mut path)) => {
let pos = path.segments.len();
path.segments.push_punct(colon2_token);
path.segments.extend(rest.into_pairs());
(pos, Some(as_token), path)
}
None => {
let path = Path {
leading_colon: Some(colon2_token),
segments: rest,
};
(0, None, path)
}
};
let qself = QSelf {
lt_token,
ty: Box::new(this),
position,
as_token,
gt_token,
};
Ok((Some(qself), path))
} else {
let path = Path::parse_helper(input, expr_style)?;
Ok((None, path))
}
}
}
#[cfg(feature = "printing")]
pub(crate) mod printing {
use crate::generics;
use crate::path::{
AngleBracketedGenericArguments, AssocConst, AssocType, Constraint, GenericArgument,
ParenthesizedGenericArguments, Path, PathArguments, PathSegment, QSelf,
};
use crate::print::TokensOrDefault;
#[cfg(feature = "parsing")]
use crate::spanned::Spanned;
#[cfg(feature = "parsing")]
use proc_macro2::Span;
use proc_macro2::TokenStream;
use quote::ToTokens;
use std::cmp;
pub(crate) enum PathStyle {
Expr,
Mod,
AsWritten,
}
impl Copy for PathStyle {}
impl Clone for PathStyle {
fn clone(&self) -> Self {
*self
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for Path {
fn to_tokens(&self, tokens: &mut TokenStream) {
print_path(tokens, self, PathStyle::AsWritten);
}
}
pub(crate) fn print_path(tokens: &mut TokenStream, path: &Path, style: PathStyle) {
path.leading_colon.to_tokens(tokens);
for segment in path.segments.pairs() {
print_path_segment(tokens, segment.value(), style);
segment.punct().to_tokens(tokens);
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for PathSegment {
fn to_tokens(&self, tokens: &mut TokenStream) {
print_path_segment(tokens, self, PathStyle::AsWritten);
}
}
fn print_path_segment(tokens: &mut TokenStream, segment: &PathSegment, style: PathStyle) {
segment.ident.to_tokens(tokens);
print_path_arguments(tokens, &segment.arguments, style);
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for PathArguments {
fn to_tokens(&self, tokens: &mut TokenStream) {
print_path_arguments(tokens, self, PathStyle::AsWritten);
}
}
fn print_path_arguments(tokens: &mut TokenStream, arguments: &PathArguments, style: PathStyle) {
match arguments {
PathArguments::None => {}
PathArguments::AngleBracketed(arguments) => {
print_angle_bracketed_generic_arguments(tokens, arguments, style);
}
PathArguments::Parenthesized(arguments) => {
print_parenthesized_generic_arguments(tokens, arguments, style);
}
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for GenericArgument {
#[allow(clippy::match_same_arms)]
fn to_tokens(&self, tokens: &mut TokenStream) {
match self {
GenericArgument::Lifetime(lt) => lt.to_tokens(tokens),
GenericArgument::Type(ty) => ty.to_tokens(tokens),
GenericArgument::Const(expr) => {
generics::printing::print_const_argument(expr, tokens);
}
GenericArgument::AssocType(assoc) => assoc.to_tokens(tokens),
GenericArgument::AssocConst(assoc) => assoc.to_tokens(tokens),
GenericArgument::Constraint(constraint) => constraint.to_tokens(tokens),
}
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for AngleBracketedGenericArguments {
fn to_tokens(&self, tokens: &mut TokenStream) {
print_angle_bracketed_generic_arguments(tokens, self, PathStyle::AsWritten);
}
}
pub(crate) fn print_angle_bracketed_generic_arguments(
tokens: &mut TokenStream,
arguments: &AngleBracketedGenericArguments,
style: PathStyle,
) {
if let PathStyle::Mod = style {
return;
}
conditionally_print_turbofish(tokens, &arguments.colon2_token, style);
arguments.lt_token.to_tokens(tokens);
// Print lifetimes before types/consts/bindings, regardless of their
// order in args.
let mut trailing_or_empty = true;
for param in arguments.args.pairs() {
match param.value() {
GenericArgument::Lifetime(_) => {
param.to_tokens(tokens);
trailing_or_empty = param.punct().is_some();
}
GenericArgument::Type(_)
| GenericArgument::Const(_)
| GenericArgument::AssocType(_)
| GenericArgument::AssocConst(_)
| GenericArgument::Constraint(_) => {}
}
}
for param in arguments.args.pairs() {
match param.value() {
GenericArgument::Type(_)
| GenericArgument::Const(_)
| GenericArgument::AssocType(_)
| GenericArgument::AssocConst(_)
| GenericArgument::Constraint(_) => {
if !trailing_or_empty {
<Token![,]>::default().to_tokens(tokens);
}
param.to_tokens(tokens);
trailing_or_empty = param.punct().is_some();
}
GenericArgument::Lifetime(_) => {}
}
}
arguments.gt_token.to_tokens(tokens);
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for AssocType {
fn to_tokens(&self, tokens: &mut TokenStream) {
self.ident.to_tokens(tokens);
self.generics.to_tokens(tokens);
self.eq_token.to_tokens(tokens);
self.ty.to_tokens(tokens);
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for AssocConst {
fn to_tokens(&self, tokens: &mut TokenStream) {
self.ident.to_tokens(tokens);
self.generics.to_tokens(tokens);
self.eq_token.to_tokens(tokens);
generics::printing::print_const_argument(&self.value, tokens);
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for Constraint {
fn to_tokens(&self, tokens: &mut TokenStream) {
self.ident.to_tokens(tokens);
self.generics.to_tokens(tokens);
self.colon_token.to_tokens(tokens);
self.bounds.to_tokens(tokens);
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for ParenthesizedGenericArguments {
fn to_tokens(&self, tokens: &mut TokenStream) {
print_parenthesized_generic_arguments(tokens, self, PathStyle::AsWritten);
}
}
fn print_parenthesized_generic_arguments(
tokens: &mut TokenStream,
arguments: &ParenthesizedGenericArguments,
style: PathStyle,
) {
if let PathStyle::Mod = style {
return;
}
conditionally_print_turbofish(tokens, &None, style);
arguments.paren_token.surround(tokens, |tokens| {
arguments.inputs.to_tokens(tokens);
});
arguments.output.to_tokens(tokens);
}
pub(crate) fn print_qpath(
tokens: &mut TokenStream,
qself: &Option<QSelf>,
path: &Path,
style: PathStyle,
) {
let qself = match qself {
Some(qself) => qself,
None => {
print_path(tokens, path, style);
return;
}
};
qself.lt_token.to_tokens(tokens);
qself.ty.to_tokens(tokens);
let pos = cmp::min(qself.position, path.segments.len());
let mut segments = path.segments.pairs();
if pos > 0 {
TokensOrDefault(&qself.as_token).to_tokens(tokens);
path.leading_colon.to_tokens(tokens);
for (i, segment) in segments.by_ref().take(pos).enumerate() {
print_path_segment(tokens, segment.value(), PathStyle::AsWritten);
if i + 1 == pos {
qself.gt_token.to_tokens(tokens);
}
segment.punct().to_tokens(tokens);
}
} else {
qself.gt_token.to_tokens(tokens);
path.leading_colon.to_tokens(tokens);
}
for segment in segments {
print_path_segment(tokens, segment.value(), style);
segment.punct().to_tokens(tokens);
}
}
fn conditionally_print_turbofish(
tokens: &mut TokenStream,
colon2_token: &Option<Token![::]>,
style: PathStyle,
) {
match style {
PathStyle::Expr => TokensOrDefault(colon2_token).to_tokens(tokens),
PathStyle::Mod => unreachable!(),
PathStyle::AsWritten => colon2_token.to_tokens(tokens),
}
}
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(all(feature = "parsing", feature = "printing"))))]
impl Spanned for QSelf {
fn span(&self) -> Span {
struct QSelfDelimiters<'a>(&'a QSelf);
impl<'a> ToTokens for QSelfDelimiters<'a> {
fn to_tokens(&self, tokens: &mut TokenStream) {
self.0.lt_token.to_tokens(tokens);
self.0.gt_token.to_tokens(tokens);
}
}
QSelfDelimiters(self).span()
}
}
}

210
rust/syn/precedence.rs Normal file
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#[cfg(all(feature = "printing", feature = "full"))]
use crate::attr::{AttrStyle, Attribute};
#[cfg(feature = "printing")]
use crate::expr::Expr;
#[cfg(all(feature = "printing", feature = "full"))]
use crate::expr::{
ExprArray, ExprAsync, ExprAwait, ExprBlock, ExprBreak, ExprCall, ExprConst, ExprContinue,
ExprField, ExprForLoop, ExprGroup, ExprIf, ExprIndex, ExprInfer, ExprLit, ExprLoop, ExprMacro,
ExprMatch, ExprMethodCall, ExprParen, ExprPath, ExprRepeat, ExprReturn, ExprStruct, ExprTry,
ExprTryBlock, ExprTuple, ExprUnsafe, ExprWhile, ExprYield,
};
use crate::op::BinOp;
#[cfg(all(feature = "printing", feature = "full"))]
use crate::ty::ReturnType;
use std::cmp::Ordering;
// Reference: https://doc.rust-lang.org/reference/expressions.html#expression-precedence
pub(crate) enum Precedence {
// return, break, closures
Jump,
// = += -= *= /= %= &= |= ^= <<= >>=
Assign,
// .. ..=
Range,
// ||
Or,
// &&
And,
// let
#[cfg(feature = "printing")]
Let,
// == != < > <= >=
Compare,
// |
BitOr,
// ^
BitXor,
// &
BitAnd,
// << >>
Shift,
// + -
Sum,
// * / %
Product,
// as
Cast,
// unary - * ! & &mut
#[cfg(feature = "printing")]
Prefix,
// paths, loops, function calls, array indexing, field expressions, method calls
#[cfg(feature = "printing")]
Unambiguous,
}
impl Precedence {
pub(crate) const MIN: Self = Precedence::Jump;
pub(crate) fn of_binop(op: &BinOp) -> Self {
match op {
BinOp::Add(_) | BinOp::Sub(_) => Precedence::Sum,
BinOp::Mul(_) | BinOp::Div(_) | BinOp::Rem(_) => Precedence::Product,
BinOp::And(_) => Precedence::And,
BinOp::Or(_) => Precedence::Or,
BinOp::BitXor(_) => Precedence::BitXor,
BinOp::BitAnd(_) => Precedence::BitAnd,
BinOp::BitOr(_) => Precedence::BitOr,
BinOp::Shl(_) | BinOp::Shr(_) => Precedence::Shift,
BinOp::Eq(_)
| BinOp::Lt(_)
| BinOp::Le(_)
| BinOp::Ne(_)
| BinOp::Ge(_)
| BinOp::Gt(_) => Precedence::Compare,
BinOp::AddAssign(_)
| BinOp::SubAssign(_)
| BinOp::MulAssign(_)
| BinOp::DivAssign(_)
| BinOp::RemAssign(_)
| BinOp::BitXorAssign(_)
| BinOp::BitAndAssign(_)
| BinOp::BitOrAssign(_)
| BinOp::ShlAssign(_)
| BinOp::ShrAssign(_) => Precedence::Assign,
}
}
#[cfg(feature = "printing")]
pub(crate) fn of(e: &Expr) -> Self {
#[cfg(feature = "full")]
fn prefix_attrs(attrs: &[Attribute]) -> Precedence {
for attr in attrs {
if let AttrStyle::Outer = attr.style {
return Precedence::Prefix;
}
}
Precedence::Unambiguous
}
match e {
#[cfg(feature = "full")]
Expr::Closure(e) => match e.output {
ReturnType::Default => Precedence::Jump,
ReturnType::Type(..) => prefix_attrs(&e.attrs),
},
#[cfg(feature = "full")]
Expr::Break(ExprBreak { expr, .. })
| Expr::Return(ExprReturn { expr, .. })
| Expr::Yield(ExprYield { expr, .. }) => match expr {
Some(_) => Precedence::Jump,
None => Precedence::Unambiguous,
},
Expr::Assign(_) => Precedence::Assign,
Expr::Range(_) => Precedence::Range,
Expr::Binary(e) => Precedence::of_binop(&e.op),
Expr::Let(_) => Precedence::Let,
Expr::Cast(_) => Precedence::Cast,
Expr::RawAddr(_) | Expr::Reference(_) | Expr::Unary(_) => Precedence::Prefix,
#[cfg(feature = "full")]
Expr::Array(ExprArray { attrs, .. })
| Expr::Async(ExprAsync { attrs, .. })
| Expr::Await(ExprAwait { attrs, .. })
| Expr::Block(ExprBlock { attrs, .. })
| Expr::Call(ExprCall { attrs, .. })
| Expr::Const(ExprConst { attrs, .. })
| Expr::Continue(ExprContinue { attrs, .. })
| Expr::Field(ExprField { attrs, .. })
| Expr::ForLoop(ExprForLoop { attrs, .. })
| Expr::Group(ExprGroup { attrs, .. })
| Expr::If(ExprIf { attrs, .. })
| Expr::Index(ExprIndex { attrs, .. })
| Expr::Infer(ExprInfer { attrs, .. })
| Expr::Lit(ExprLit { attrs, .. })
| Expr::Loop(ExprLoop { attrs, .. })
| Expr::Macro(ExprMacro { attrs, .. })
| Expr::Match(ExprMatch { attrs, .. })
| Expr::MethodCall(ExprMethodCall { attrs, .. })
| Expr::Paren(ExprParen { attrs, .. })
| Expr::Path(ExprPath { attrs, .. })
| Expr::Repeat(ExprRepeat { attrs, .. })
| Expr::Struct(ExprStruct { attrs, .. })
| Expr::Try(ExprTry { attrs, .. })
| Expr::TryBlock(ExprTryBlock { attrs, .. })
| Expr::Tuple(ExprTuple { attrs, .. })
| Expr::Unsafe(ExprUnsafe { attrs, .. })
| Expr::While(ExprWhile { attrs, .. }) => prefix_attrs(attrs),
#[cfg(not(feature = "full"))]
Expr::Array(_)
| Expr::Async(_)
| Expr::Await(_)
| Expr::Block(_)
| Expr::Call(_)
| Expr::Const(_)
| Expr::Continue(_)
| Expr::Field(_)
| Expr::ForLoop(_)
| Expr::Group(_)
| Expr::If(_)
| Expr::Index(_)
| Expr::Infer(_)
| Expr::Lit(_)
| Expr::Loop(_)
| Expr::Macro(_)
| Expr::Match(_)
| Expr::MethodCall(_)
| Expr::Paren(_)
| Expr::Path(_)
| Expr::Repeat(_)
| Expr::Struct(_)
| Expr::Try(_)
| Expr::TryBlock(_)
| Expr::Tuple(_)
| Expr::Unsafe(_)
| Expr::While(_) => Precedence::Unambiguous,
Expr::Verbatim(_) => Precedence::Unambiguous,
#[cfg(not(feature = "full"))]
Expr::Break(_) | Expr::Closure(_) | Expr::Return(_) | Expr::Yield(_) => unreachable!(),
}
}
}
impl Copy for Precedence {}
impl Clone for Precedence {
fn clone(&self) -> Self {
*self
}
}
impl PartialEq for Precedence {
fn eq(&self, other: &Self) -> bool {
*self as u8 == *other as u8
}
}
impl PartialOrd for Precedence {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
let this = *self as u8;
let other = *other as u8;
Some(this.cmp(&other))
}
}

16
rust/syn/print.rs Normal file
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use proc_macro2::TokenStream;
use quote::ToTokens;
pub(crate) struct TokensOrDefault<'a, T: 'a>(pub &'a Option<T>);
impl<'a, T> ToTokens for TokensOrDefault<'a, T>
where
T: ToTokens + Default,
{
fn to_tokens(&self, tokens: &mut TokenStream) {
match self.0 {
Some(t) => t.to_tokens(tokens),
None => T::default().to_tokens(tokens),
}
}
}

1155
rust/syn/punctuated.rs Normal file
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178
rust/syn/restriction.rs Normal file
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use crate::path::Path;
use crate::token;
ast_enum! {
/// The visibility level of an item: inherited or `pub` or
/// `pub(restricted)`.
///
/// # Syntax tree enum
///
/// This type is a [syntax tree enum].
///
/// [syntax tree enum]: crate::expr::Expr#syntax-tree-enums
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub enum Visibility {
/// A public visibility level: `pub`.
Public(Token![pub]),
/// A visibility level restricted to some path: `pub(self)` or
/// `pub(super)` or `pub(crate)` or `pub(in some::module)`.
Restricted(VisRestricted),
/// An inherited visibility, which usually means private.
Inherited,
}
}
ast_struct! {
/// A visibility level restricted to some path: `pub(self)` or
/// `pub(super)` or `pub(crate)` or `pub(in some::module)`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct VisRestricted {
pub pub_token: Token![pub],
pub paren_token: token::Paren,
pub in_token: Option<Token![in]>,
pub path: Box<Path>,
}
}
ast_enum! {
/// Unused, but reserved for RFC 3323 restrictions.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
#[non_exhaustive]
pub enum FieldMutability {
None,
// TODO: https://rust-lang.github.io/rfcs/3323-restrictions.html
//
// FieldMutability::Restricted(MutRestricted)
//
// pub struct MutRestricted {
// pub mut_token: Token![mut],
// pub paren_token: token::Paren,
// pub in_token: Option<Token![in]>,
// pub path: Box<Path>,
// }
}
}
#[cfg(feature = "parsing")]
pub(crate) mod parsing {
use crate::error::Result;
use crate::ext::IdentExt as _;
use crate::ident::Ident;
use crate::parse::discouraged::Speculative as _;
use crate::parse::{Parse, ParseStream};
use crate::path::Path;
use crate::restriction::{VisRestricted, Visibility};
use crate::token;
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for Visibility {
fn parse(input: ParseStream) -> Result<Self> {
// Recognize an empty None-delimited group, as produced by a $:vis
// matcher that matched no tokens.
if input.peek(token::Group) {
let ahead = input.fork();
let group = crate::group::parse_group(&ahead)?;
if group.content.is_empty() {
input.advance_to(&ahead);
return Ok(Visibility::Inherited);
}
}
if input.peek(Token![pub]) {
Self::parse_pub(input)
} else {
Ok(Visibility::Inherited)
}
}
}
impl Visibility {
fn parse_pub(input: ParseStream) -> Result<Self> {
let pub_token = input.parse::<Token![pub]>()?;
if input.peek(token::Paren) {
let ahead = input.fork();
let content;
let paren_token = parenthesized!(content in ahead);
if content.peek(Token![crate])
|| content.peek(Token![self])
|| content.peek(Token![super])
{
let path = content.call(Ident::parse_any)?;
// Ensure there are no additional tokens within `content`.
// Without explicitly checking, we may misinterpret a tuple
// field as a restricted visibility, causing a parse error.
// e.g. `pub (crate::A, crate::B)` (Issue #720).
if content.is_empty() {
input.advance_to(&ahead);
return Ok(Visibility::Restricted(VisRestricted {
pub_token,
paren_token,
in_token: None,
path: Box::new(Path::from(path)),
}));
}
} else if content.peek(Token![in]) {
let in_token: Token![in] = content.parse()?;
let path = content.call(Path::parse_mod_style)?;
input.advance_to(&ahead);
return Ok(Visibility::Restricted(VisRestricted {
pub_token,
paren_token,
in_token: Some(in_token),
path: Box::new(path),
}));
}
}
Ok(Visibility::Public(pub_token))
}
#[cfg(feature = "full")]
pub(crate) fn is_some(&self) -> bool {
match self {
Visibility::Inherited => false,
_ => true,
}
}
}
}
#[cfg(feature = "printing")]
mod printing {
use crate::path;
use crate::path::printing::PathStyle;
use crate::restriction::{VisRestricted, Visibility};
use proc_macro2::TokenStream;
use quote::ToTokens;
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for Visibility {
fn to_tokens(&self, tokens: &mut TokenStream) {
match self {
Visibility::Public(pub_token) => pub_token.to_tokens(tokens),
Visibility::Restricted(vis_restricted) => vis_restricted.to_tokens(tokens),
Visibility::Inherited => {}
}
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for VisRestricted {
fn to_tokens(&self, tokens: &mut TokenStream) {
self.pub_token.to_tokens(tokens);
self.paren_token.surround(tokens, |tokens| {
// TODO: If we have a path which is not "self" or "super" or
// "crate", automatically add the "in" token.
self.in_token.to_tokens(tokens);
path::printing::print_path(tokens, &self.path, PathStyle::Mod);
});
}
}
}

265
rust/syn/scan_expr.rs Normal file
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use self::{Action::*, Input::*};
use proc_macro2::{Delimiter, Ident, Spacing, TokenTree};
use syn::parse::{ParseStream, Result};
use syn::{AngleBracketedGenericArguments, BinOp, Expr, ExprPath, Lifetime, Lit, Token, Type};
enum Input {
Keyword(&'static str),
Punct(&'static str),
ConsumeAny,
ConsumeBinOp,
ConsumeBrace,
ConsumeDelimiter,
ConsumeIdent,
ConsumeLifetime,
ConsumeLiteral,
ConsumeNestedBrace,
ExpectPath,
ExpectTurbofish,
ExpectType,
CanBeginExpr,
Otherwise,
Empty,
}
enum Action {
SetState(&'static [(Input, Action)]),
IncDepth,
DecDepth,
Finish,
}
static INIT: [(Input, Action); 28] = [
(ConsumeDelimiter, SetState(&POSTFIX)),
(Keyword("async"), SetState(&ASYNC)),
(Keyword("break"), SetState(&BREAK_LABEL)),
(Keyword("const"), SetState(&CONST)),
(Keyword("continue"), SetState(&CONTINUE)),
(Keyword("for"), SetState(&FOR)),
(Keyword("if"), IncDepth),
(Keyword("let"), SetState(&PATTERN)),
(Keyword("loop"), SetState(&BLOCK)),
(Keyword("match"), IncDepth),
(Keyword("move"), SetState(&CLOSURE)),
(Keyword("return"), SetState(&RETURN)),
(Keyword("static"), SetState(&CLOSURE)),
(Keyword("unsafe"), SetState(&BLOCK)),
(Keyword("while"), IncDepth),
(Keyword("yield"), SetState(&RETURN)),
(Keyword("_"), SetState(&POSTFIX)),
(Punct("!"), SetState(&INIT)),
(Punct("#"), SetState(&[(ConsumeDelimiter, SetState(&INIT))])),
(Punct("&"), SetState(&REFERENCE)),
(Punct("*"), SetState(&INIT)),
(Punct("-"), SetState(&INIT)),
(Punct("..="), SetState(&INIT)),
(Punct(".."), SetState(&RANGE)),
(Punct("|"), SetState(&CLOSURE_ARGS)),
(ConsumeLifetime, SetState(&[(Punct(":"), SetState(&INIT))])),
(ConsumeLiteral, SetState(&POSTFIX)),
(ExpectPath, SetState(&PATH)),
];
static POSTFIX: [(Input, Action); 10] = [
(Keyword("as"), SetState(&[(ExpectType, SetState(&POSTFIX))])),
(Punct("..="), SetState(&INIT)),
(Punct(".."), SetState(&RANGE)),
(Punct("."), SetState(&DOT)),
(Punct("?"), SetState(&POSTFIX)),
(ConsumeBinOp, SetState(&INIT)),
(Punct("="), SetState(&INIT)),
(ConsumeNestedBrace, SetState(&IF_THEN)),
(ConsumeDelimiter, SetState(&POSTFIX)),
(Empty, Finish),
];
static ASYNC: [(Input, Action); 3] = [
(Keyword("move"), SetState(&ASYNC)),
(Punct("|"), SetState(&CLOSURE_ARGS)),
(ConsumeBrace, SetState(&POSTFIX)),
];
static BLOCK: [(Input, Action); 1] = [(ConsumeBrace, SetState(&POSTFIX))];
static BREAK_LABEL: [(Input, Action); 2] = [
(ConsumeLifetime, SetState(&BREAK_VALUE)),
(Otherwise, SetState(&BREAK_VALUE)),
];
static BREAK_VALUE: [(Input, Action); 3] = [
(ConsumeNestedBrace, SetState(&IF_THEN)),
(CanBeginExpr, SetState(&INIT)),
(Otherwise, SetState(&POSTFIX)),
];
static CLOSURE: [(Input, Action); 7] = [
(Keyword("async"), SetState(&CLOSURE)),
(Keyword("move"), SetState(&CLOSURE)),
(Punct(","), SetState(&CLOSURE)),
(Punct(">"), SetState(&CLOSURE)),
(Punct("|"), SetState(&CLOSURE_ARGS)),
(ConsumeLifetime, SetState(&CLOSURE)),
(ConsumeIdent, SetState(&CLOSURE)),
];
static CLOSURE_ARGS: [(Input, Action); 2] = [
(Punct("|"), SetState(&CLOSURE_RET)),
(ConsumeAny, SetState(&CLOSURE_ARGS)),
];
static CLOSURE_RET: [(Input, Action); 2] = [
(Punct("->"), SetState(&[(ExpectType, SetState(&BLOCK))])),
(Otherwise, SetState(&INIT)),
];
static CONST: [(Input, Action); 2] = [
(Punct("|"), SetState(&CLOSURE_ARGS)),
(ConsumeBrace, SetState(&POSTFIX)),
];
static CONTINUE: [(Input, Action); 2] = [
(ConsumeLifetime, SetState(&POSTFIX)),
(Otherwise, SetState(&POSTFIX)),
];
static DOT: [(Input, Action); 3] = [
(Keyword("await"), SetState(&POSTFIX)),
(ConsumeIdent, SetState(&METHOD)),
(ConsumeLiteral, SetState(&POSTFIX)),
];
static FOR: [(Input, Action); 2] = [
(Punct("<"), SetState(&CLOSURE)),
(Otherwise, SetState(&PATTERN)),
];
static IF_ELSE: [(Input, Action); 2] = [(Keyword("if"), SetState(&INIT)), (ConsumeBrace, DecDepth)];
static IF_THEN: [(Input, Action); 2] =
[(Keyword("else"), SetState(&IF_ELSE)), (Otherwise, DecDepth)];
static METHOD: [(Input, Action); 1] = [(ExpectTurbofish, SetState(&POSTFIX))];
static PATH: [(Input, Action); 4] = [
(Punct("!="), SetState(&INIT)),
(Punct("!"), SetState(&INIT)),
(ConsumeNestedBrace, SetState(&IF_THEN)),
(Otherwise, SetState(&POSTFIX)),
];
static PATTERN: [(Input, Action); 15] = [
(ConsumeDelimiter, SetState(&PATTERN)),
(Keyword("box"), SetState(&PATTERN)),
(Keyword("in"), IncDepth),
(Keyword("mut"), SetState(&PATTERN)),
(Keyword("ref"), SetState(&PATTERN)),
(Keyword("_"), SetState(&PATTERN)),
(Punct("!"), SetState(&PATTERN)),
(Punct("&"), SetState(&PATTERN)),
(Punct("..="), SetState(&PATTERN)),
(Punct(".."), SetState(&PATTERN)),
(Punct("="), SetState(&INIT)),
(Punct("@"), SetState(&PATTERN)),
(Punct("|"), SetState(&PATTERN)),
(ConsumeLiteral, SetState(&PATTERN)),
(ExpectPath, SetState(&PATTERN)),
];
static RANGE: [(Input, Action); 6] = [
(Punct("..="), SetState(&INIT)),
(Punct(".."), SetState(&RANGE)),
(Punct("."), SetState(&DOT)),
(ConsumeNestedBrace, SetState(&IF_THEN)),
(Empty, Finish),
(Otherwise, SetState(&INIT)),
];
static RAW: [(Input, Action); 3] = [
(Keyword("const"), SetState(&INIT)),
(Keyword("mut"), SetState(&INIT)),
(Otherwise, SetState(&POSTFIX)),
];
static REFERENCE: [(Input, Action); 3] = [
(Keyword("mut"), SetState(&INIT)),
(Keyword("raw"), SetState(&RAW)),
(Otherwise, SetState(&INIT)),
];
static RETURN: [(Input, Action); 2] = [
(CanBeginExpr, SetState(&INIT)),
(Otherwise, SetState(&POSTFIX)),
];
pub(crate) fn scan_expr(input: ParseStream) -> Result<()> {
let mut state = INIT.as_slice();
let mut depth = 0usize;
'table: loop {
for rule in state {
if match rule.0 {
Input::Keyword(expected) => input.step(|cursor| match cursor.ident() {
Some((ident, rest)) if ident == expected => Ok((true, rest)),
_ => Ok((false, *cursor)),
})?,
Input::Punct(expected) => input.step(|cursor| {
let begin = *cursor;
let mut cursor = begin;
for (i, ch) in expected.chars().enumerate() {
match cursor.punct() {
Some((punct, _)) if punct.as_char() != ch => break,
Some((_, rest)) if i == expected.len() - 1 => {
return Ok((true, rest));
}
Some((punct, rest)) if punct.spacing() == Spacing::Joint => {
cursor = rest;
}
_ => break,
}
}
Ok((false, begin))
})?,
Input::ConsumeAny => input.parse::<Option<TokenTree>>()?.is_some(),
Input::ConsumeBinOp => input.parse::<BinOp>().is_ok(),
Input::ConsumeBrace | Input::ConsumeNestedBrace => {
(matches!(rule.0, Input::ConsumeBrace) || depth > 0)
&& input.step(|cursor| match cursor.group(Delimiter::Brace) {
Some((_inside, _span, rest)) => Ok((true, rest)),
None => Ok((false, *cursor)),
})?
}
Input::ConsumeDelimiter => input.step(|cursor| match cursor.any_group() {
Some((_inside, _delimiter, _span, rest)) => Ok((true, rest)),
None => Ok((false, *cursor)),
})?,
Input::ConsumeIdent => input.parse::<Option<Ident>>()?.is_some(),
Input::ConsumeLifetime => input.parse::<Option<Lifetime>>()?.is_some(),
Input::ConsumeLiteral => input.parse::<Option<Lit>>()?.is_some(),
Input::ExpectPath => {
input.parse::<ExprPath>()?;
true
}
Input::ExpectTurbofish => {
if input.peek(Token![::]) {
input.parse::<AngleBracketedGenericArguments>()?;
}
true
}
Input::ExpectType => {
Type::without_plus(input)?;
true
}
Input::CanBeginExpr => Expr::peek(input),
Input::Otherwise => true,
Input::Empty => input.is_empty() || input.peek(Token![,]),
} {
state = match rule.1 {
Action::SetState(next) => next,
Action::IncDepth => (depth += 1, &INIT).1,
Action::DecDepth => (depth -= 1, &POSTFIX).1,
Action::Finish => return if depth == 0 { Ok(()) } else { break },
};
continue 'table;
}
}
return Err(input.error("unsupported expression"));
}
}

4
rust/syn/sealed.rs Normal file
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#[cfg(feature = "parsing")]
pub(crate) mod lookahead {
pub trait Sealed: Copy {}
}

63
rust/syn/span.rs Normal file
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use proc_macro2::extra::DelimSpan;
use proc_macro2::{Delimiter, Group, Span, TokenStream};
#[doc(hidden)]
pub trait IntoSpans<S> {
fn into_spans(self) -> S;
}
impl IntoSpans<Span> for Span {
fn into_spans(self) -> Span {
self
}
}
impl IntoSpans<[Span; 1]> for Span {
fn into_spans(self) -> [Span; 1] {
[self]
}
}
impl IntoSpans<[Span; 2]> for Span {
fn into_spans(self) -> [Span; 2] {
[self, self]
}
}
impl IntoSpans<[Span; 3]> for Span {
fn into_spans(self) -> [Span; 3] {
[self, self, self]
}
}
impl IntoSpans<[Span; 1]> for [Span; 1] {
fn into_spans(self) -> [Span; 1] {
self
}
}
impl IntoSpans<[Span; 2]> for [Span; 2] {
fn into_spans(self) -> [Span; 2] {
self
}
}
impl IntoSpans<[Span; 3]> for [Span; 3] {
fn into_spans(self) -> [Span; 3] {
self
}
}
impl IntoSpans<DelimSpan> for Span {
fn into_spans(self) -> DelimSpan {
let mut group = Group::new(Delimiter::None, TokenStream::new());
group.set_span(self);
group.delim_span()
}
}
impl IntoSpans<DelimSpan> for DelimSpan {
fn into_spans(self) -> DelimSpan {
self
}
}

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//! A trait that can provide the `Span` of the complete contents of a syntax
//! tree node.
//!
//! <br>
//!
//! # Example
//!
//! Suppose in a procedural macro we have a [`Type`] that we want to assert
//! implements the [`Sync`] trait. Maybe this is the type of one of the fields
//! of a struct for which we are deriving a trait implementation, and we need to
//! be able to pass a reference to one of those fields across threads.
//!
//! [`Type`]: crate::Type
//! [`Sync`]: std::marker::Sync
//!
//! If the field type does *not* implement `Sync` as required, we want the
//! compiler to report an error pointing out exactly which type it was.
//!
//! The following macro code takes a variable `ty` of type `Type` and produces a
//! static assertion that `Sync` is implemented for that type.
//!
//! ```
//! # extern crate proc_macro;
//! #
//! use proc_macro::TokenStream;
//! use proc_macro2::Span;
//! use quote::quote_spanned;
//! use syn::Type;
//! use syn::spanned::Spanned;
//!
//! # const IGNORE_TOKENS: &str = stringify! {
//! #[proc_macro_derive(MyMacro)]
//! # };
//! pub fn my_macro(input: TokenStream) -> TokenStream {
//! # let ty = get_a_type();
//! /* ... */
//!
//! let assert_sync = quote_spanned! {ty.span()=>
//! struct _AssertSync where #ty: Sync;
//! };
//!
//! /* ... */
//! # input
//! }
//! #
//! # fn get_a_type() -> Type {
//! # unimplemented!()
//! # }
//! ```
//!
//! By inserting this `assert_sync` fragment into the output code generated by
//! our macro, the user's code will fail to compile if `ty` does not implement
//! `Sync`. The errors they would see look like the following.
//!
//! ```text
//! error[E0277]: the trait bound `*const i32: std::marker::Sync` is not satisfied
//! --> src/main.rs:10:21
//! |
//! 10 | bad_field: *const i32,
//! | ^^^^^^^^^^ `*const i32` cannot be shared between threads safely
//! ```
//!
//! In this technique, using the `Type`'s span for the error message makes the
//! error appear in the correct place underlining the right type.
//!
//! <br>
//!
//! # Limitations
//!
//! The underlying [`proc_macro::Span::join`] method is nightly-only. When
//! called from within a procedural macro in a nightly compiler, `Spanned` will
//! use `join` to produce the intended span. When not using a nightly compiler,
//! only the span of the *first token* of the syntax tree node is returned.
//!
//! In the common case of wanting to use the joined span as the span of a
//! `syn::Error`, consider instead using [`syn::Error::new_spanned`] which is
//! able to span the error correctly under the complete syntax tree node without
//! needing the unstable `join`.
//!
//! [`syn::Error::new_spanned`]: crate::Error::new_spanned
use proc_macro2::Span;
use quote::spanned::Spanned as ToTokens;
/// A trait that can provide the `Span` of the complete contents of a syntax
/// tree node.
///
/// This trait is automatically implemented for all types that implement
/// [`ToTokens`] from the `quote` crate, as well as for `Span` itself.
///
/// [`ToTokens`]: quote::ToTokens
///
/// See the [module documentation] for an example.
///
/// [module documentation]: self
pub trait Spanned: private::Sealed {
/// Returns a `Span` covering the complete contents of this syntax tree
/// node, or [`Span::call_site()`] if this node is empty.
///
/// [`Span::call_site()`]: proc_macro2::Span::call_site
fn span(&self) -> Span;
}
impl<T: ?Sized + ToTokens> Spanned for T {
fn span(&self) -> Span {
self.__span()
}
}
mod private {
use crate::spanned::ToTokens;
pub trait Sealed {}
impl<T: ?Sized + ToTokens> Sealed for T {}
#[cfg(any(feature = "full", feature = "derive"))]
impl Sealed for crate::QSelf {}
}

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use crate::attr::Attribute;
use crate::expr::Expr;
use crate::item::Item;
use crate::mac::Macro;
use crate::pat::Pat;
use crate::token;
ast_struct! {
/// A braced block containing Rust statements.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct Block {
pub brace_token: token::Brace,
/// Statements in a block
pub stmts: Vec<Stmt>,
}
}
ast_enum! {
/// A statement, usually ending in a semicolon.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub enum Stmt {
/// A local (let) binding.
Local(Local),
/// An item definition.
Item(Item),
/// Expression, with or without trailing semicolon.
Expr(Expr, Option<Token![;]>),
/// A macro invocation in statement position.
///
/// Syntactically it's ambiguous which other kind of statement this
/// macro would expand to. It can be any of local variable (`let`),
/// item, or expression.
Macro(StmtMacro),
}
}
ast_struct! {
/// A local `let` binding: `let x: u64 = s.parse()?;`.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct Local {
pub attrs: Vec<Attribute>,
pub let_token: Token![let],
pub pat: Pat,
pub init: Option<LocalInit>,
pub semi_token: Token![;],
}
}
ast_struct! {
/// The expression assigned in a local `let` binding, including optional
/// diverging `else` block.
///
/// `LocalInit` represents `= s.parse()?` in `let x: u64 = s.parse()?` and
/// `= r else { return }` in `let Ok(x) = r else { return }`.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct LocalInit {
pub eq_token: Token![=],
pub expr: Box<Expr>,
pub diverge: Option<(Token![else], Box<Expr>)>,
}
}
ast_struct! {
/// A macro invocation in statement position.
///
/// Syntactically it's ambiguous which other kind of statement this macro
/// would expand to. It can be any of local variable (`let`), item, or
/// expression.
#[cfg_attr(docsrs, doc(cfg(feature = "full")))]
pub struct StmtMacro {
pub attrs: Vec<Attribute>,
pub mac: Macro,
pub semi_token: Option<Token![;]>,
}
}
#[cfg(feature = "parsing")]
pub(crate) mod parsing {
use crate::attr::Attribute;
use crate::classify;
use crate::error::Result;
use crate::expr::{Expr, ExprBlock, ExprMacro};
use crate::ident::Ident;
use crate::item;
use crate::mac::{self, Macro};
use crate::parse::discouraged::Speculative as _;
use crate::parse::{Parse, ParseStream};
use crate::pat::{Pat, PatType};
use crate::path::Path;
use crate::stmt::{Block, Local, LocalInit, Stmt, StmtMacro};
use crate::token;
use crate::ty::Type;
use proc_macro2::TokenStream;
struct AllowNoSemi(bool);
impl Block {
/// Parse the body of a block as zero or more statements, possibly
/// including one trailing expression.
///
/// # Example
///
/// ```
/// use syn::{braced, token, Attribute, Block, Ident, Result, Stmt, Token};
/// use syn::parse::{Parse, ParseStream};
///
/// // Parse a function with no generics or parameter list.
/// //
/// // fn playground {
/// // let mut x = 1;
/// // x += 1;
/// // println!("{}", x);
/// // }
/// struct MiniFunction {
/// attrs: Vec<Attribute>,
/// fn_token: Token![fn],
/// name: Ident,
/// brace_token: token::Brace,
/// stmts: Vec<Stmt>,
/// }
///
/// impl Parse for MiniFunction {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let outer_attrs = input.call(Attribute::parse_outer)?;
/// let fn_token: Token![fn] = input.parse()?;
/// let name: Ident = input.parse()?;
///
/// let content;
/// let brace_token = braced!(content in input);
/// let inner_attrs = content.call(Attribute::parse_inner)?;
/// let stmts = content.call(Block::parse_within)?;
///
/// Ok(MiniFunction {
/// attrs: {
/// let mut attrs = outer_attrs;
/// attrs.extend(inner_attrs);
/// attrs
/// },
/// fn_token,
/// name,
/// brace_token,
/// stmts,
/// })
/// }
/// }
/// ```
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_within(input: ParseStream) -> Result<Vec<Stmt>> {
let mut stmts = Vec::new();
loop {
while let semi @ Some(_) = input.parse()? {
stmts.push(Stmt::Expr(Expr::Verbatim(TokenStream::new()), semi));
}
if input.is_empty() {
break;
}
let stmt = parse_stmt(input, AllowNoSemi(true))?;
let requires_semicolon = match &stmt {
Stmt::Expr(stmt, None) => classify::requires_semi_to_be_stmt(stmt),
Stmt::Macro(stmt) => {
stmt.semi_token.is_none() && !stmt.mac.delimiter.is_brace()
}
Stmt::Local(_) | Stmt::Item(_) | Stmt::Expr(_, Some(_)) => false,
};
stmts.push(stmt);
if input.is_empty() {
break;
} else if requires_semicolon {
return Err(input.error("unexpected token, expected `;`"));
}
}
Ok(stmts)
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for Block {
fn parse(input: ParseStream) -> Result<Self> {
let content;
Ok(Block {
brace_token: braced!(content in input),
stmts: content.call(Block::parse_within)?,
})
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for Stmt {
fn parse(input: ParseStream) -> Result<Self> {
let allow_nosemi = AllowNoSemi(false);
parse_stmt(input, allow_nosemi)
}
}
fn parse_stmt(input: ParseStream, allow_nosemi: AllowNoSemi) -> Result<Stmt> {
let begin = input.fork();
let attrs = input.call(Attribute::parse_outer)?;
// brace-style macros; paren and bracket macros get parsed as
// expression statements.
let ahead = input.fork();
let mut is_item_macro = false;
if let Ok(path) = ahead.call(Path::parse_mod_style) {
if ahead.peek(Token![!]) {
if ahead.peek2(Ident) || ahead.peek2(Token![try]) {
is_item_macro = true;
} else if ahead.peek2(token::Brace)
&& !(ahead.peek3(Token![.]) && !ahead.peek3(Token![..])
|| ahead.peek3(Token![?]))
{
input.advance_to(&ahead);
return stmt_mac(input, attrs, path).map(Stmt::Macro);
}
}
}
if input.peek(Token![let]) && !input.peek(token::Group) {
stmt_local(input, attrs).map(Stmt::Local)
} else if input.peek(Token![pub])
|| input.peek(Token![crate]) && !input.peek2(Token![::])
|| input.peek(Token![extern])
|| input.peek(Token![use])
|| input.peek(Token![static])
&& (input.peek2(Token![mut])
|| input.peek2(Ident)
&& !(input.peek2(Token![async])
&& (input.peek3(Token![move]) || input.peek3(Token![|]))))
|| input.peek(Token![const])
&& !(input.peek2(token::Brace)
|| input.peek2(Token![static])
|| input.peek2(Token![async])
&& !(input.peek3(Token![unsafe])
|| input.peek3(Token![extern])
|| input.peek3(Token![fn]))
|| input.peek2(Token![move])
|| input.peek2(Token![|]))
|| input.peek(Token![unsafe]) && !input.peek2(token::Brace)
|| input.peek(Token![async])
&& (input.peek2(Token![unsafe])
|| input.peek2(Token![extern])
|| input.peek2(Token![fn]))
|| input.peek(Token![fn])
|| input.peek(Token![mod])
|| input.peek(Token![type])
|| input.peek(Token![struct])
|| input.peek(Token![enum])
|| input.peek(Token![union]) && input.peek2(Ident)
|| input.peek(Token![auto]) && input.peek2(Token![trait])
|| input.peek(Token![trait])
|| input.peek(Token![default])
&& (input.peek2(Token![unsafe]) || input.peek2(Token![impl]))
|| input.peek(Token![impl])
|| input.peek(Token![macro])
|| is_item_macro
{
let item = item::parsing::parse_rest_of_item(begin, attrs, input)?;
Ok(Stmt::Item(item))
} else {
stmt_expr(input, allow_nosemi, attrs)
}
}
fn stmt_mac(input: ParseStream, attrs: Vec<Attribute>, path: Path) -> Result<StmtMacro> {
let bang_token: Token![!] = input.parse()?;
let (delimiter, tokens) = mac::parse_delimiter(input)?;
let semi_token: Option<Token![;]> = input.parse()?;
Ok(StmtMacro {
attrs,
mac: Macro {
path,
bang_token,
delimiter,
tokens,
},
semi_token,
})
}
fn stmt_local(input: ParseStream, attrs: Vec<Attribute>) -> Result<Local> {
let let_token: Token![let] = input.parse()?;
let mut pat = Pat::parse_single(input)?;
if input.peek(Token![:]) {
let colon_token: Token![:] = input.parse()?;
let ty: Type = input.parse()?;
pat = Pat::Type(PatType {
attrs: Vec::new(),
pat: Box::new(pat),
colon_token,
ty: Box::new(ty),
});
}
let init = if let Some(eq_token) = input.parse()? {
let eq_token: Token![=] = eq_token;
let expr: Expr = input.parse()?;
let diverge = if !classify::expr_trailing_brace(&expr) && input.peek(Token![else]) {
let else_token: Token![else] = input.parse()?;
let diverge = ExprBlock {
attrs: Vec::new(),
label: None,
block: input.parse()?,
};
Some((else_token, Box::new(Expr::Block(diverge))))
} else {
None
};
Some(LocalInit {
eq_token,
expr: Box::new(expr),
diverge,
})
} else {
None
};
let semi_token: Token![;] = input.parse()?;
Ok(Local {
attrs,
let_token,
pat,
init,
semi_token,
})
}
fn stmt_expr(
input: ParseStream,
allow_nosemi: AllowNoSemi,
mut attrs: Vec<Attribute>,
) -> Result<Stmt> {
let mut e = Expr::parse_with_earlier_boundary_rule(input)?;
let mut attr_target = &mut e;
loop {
attr_target = match attr_target {
Expr::Assign(e) => &mut e.left,
Expr::Binary(e) => &mut e.left,
Expr::Cast(e) => &mut e.expr,
Expr::Array(_)
| Expr::Async(_)
| Expr::Await(_)
| Expr::Block(_)
| Expr::Break(_)
| Expr::Call(_)
| Expr::Closure(_)
| Expr::Const(_)
| Expr::Continue(_)
| Expr::Field(_)
| Expr::ForLoop(_)
| Expr::Group(_)
| Expr::If(_)
| Expr::Index(_)
| Expr::Infer(_)
| Expr::Let(_)
| Expr::Lit(_)
| Expr::Loop(_)
| Expr::Macro(_)
| Expr::Match(_)
| Expr::MethodCall(_)
| Expr::Paren(_)
| Expr::Path(_)
| Expr::Range(_)
| Expr::RawAddr(_)
| Expr::Reference(_)
| Expr::Repeat(_)
| Expr::Return(_)
| Expr::Struct(_)
| Expr::Try(_)
| Expr::TryBlock(_)
| Expr::Tuple(_)
| Expr::Unary(_)
| Expr::Unsafe(_)
| Expr::While(_)
| Expr::Yield(_)
| Expr::Verbatim(_) => break,
};
}
attrs.extend(attr_target.replace_attrs(Vec::new()));
attr_target.replace_attrs(attrs);
let semi_token: Option<Token![;]> = input.parse()?;
match e {
Expr::Macro(ExprMacro { attrs, mac })
if semi_token.is_some() || mac.delimiter.is_brace() =>
{
return Ok(Stmt::Macro(StmtMacro {
attrs,
mac,
semi_token,
}));
}
_ => {}
}
if semi_token.is_some() {
Ok(Stmt::Expr(e, semi_token))
} else if allow_nosemi.0 || !classify::requires_semi_to_be_stmt(&e) {
Ok(Stmt::Expr(e, None))
} else {
Err(input.error("expected semicolon"))
}
}
}
#[cfg(feature = "printing")]
pub(crate) mod printing {
use crate::classify;
use crate::expr::{self, Expr};
use crate::fixup::FixupContext;
use crate::stmt::{Block, Local, Stmt, StmtMacro};
use crate::token;
use proc_macro2::TokenStream;
use quote::{ToTokens, TokenStreamExt};
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for Block {
fn to_tokens(&self, tokens: &mut TokenStream) {
self.brace_token.surround(tokens, |tokens| {
tokens.append_all(&self.stmts);
});
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for Stmt {
fn to_tokens(&self, tokens: &mut TokenStream) {
match self {
Stmt::Local(local) => local.to_tokens(tokens),
Stmt::Item(item) => item.to_tokens(tokens),
Stmt::Expr(expr, semi) => {
expr::printing::print_expr(expr, tokens, FixupContext::new_stmt());
semi.to_tokens(tokens);
}
Stmt::Macro(mac) => mac.to_tokens(tokens),
}
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for Local {
fn to_tokens(&self, tokens: &mut TokenStream) {
expr::printing::outer_attrs_to_tokens(&self.attrs, tokens);
self.let_token.to_tokens(tokens);
self.pat.to_tokens(tokens);
if let Some(init) = &self.init {
init.eq_token.to_tokens(tokens);
expr::printing::print_subexpression(
&init.expr,
init.diverge.is_some() && classify::expr_trailing_brace(&init.expr),
tokens,
FixupContext::NONE,
);
if let Some((else_token, diverge)) = &init.diverge {
else_token.to_tokens(tokens);
match &**diverge {
Expr::Block(diverge) => diverge.to_tokens(tokens),
_ => token::Brace::default().surround(tokens, |tokens| {
expr::printing::print_expr(diverge, tokens, FixupContext::new_stmt());
}),
}
}
}
self.semi_token.to_tokens(tokens);
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for StmtMacro {
fn to_tokens(&self, tokens: &mut TokenStream) {
expr::printing::outer_attrs_to_tokens(&self.attrs, tokens);
self.mac.to_tokens(tokens);
self.semi_token.to_tokens(tokens);
}
}
}

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use std::fmt::{self, Debug};
use std::thread::{self, ThreadId};
/// ThreadBound is a Sync-maker and Send-maker that allows accessing a value
/// of type T only from the original thread on which the ThreadBound was
/// constructed.
pub(crate) struct ThreadBound<T> {
value: T,
thread_id: ThreadId,
}
unsafe impl<T> Sync for ThreadBound<T> {}
// Send bound requires Copy, as otherwise Drop could run in the wrong place.
//
// Today Copy and Drop are mutually exclusive so `T: Copy` implies `T: !Drop`.
// This impl needs to be revisited if that restriction is relaxed in the future.
unsafe impl<T: Copy> Send for ThreadBound<T> {}
impl<T> ThreadBound<T> {
pub(crate) fn new(value: T) -> Self {
ThreadBound {
value,
thread_id: thread::current().id(),
}
}
pub(crate) fn get(&self) -> Option<&T> {
if thread::current().id() == self.thread_id {
Some(&self.value)
} else {
None
}
}
}
impl<T: Debug> Debug for ThreadBound<T> {
fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
match self.get() {
Some(value) => Debug::fmt(value, formatter),
None => formatter.write_str("unknown"),
}
}
}
// Copy the bytes of T, even if the currently running thread is the "wrong"
// thread. This is fine as long as the original thread is not simultaneously
// mutating this value via interior mutability, which would be a data race.
//
// Currently `T: Copy` is sufficient to guarantee that T contains no interior
// mutability, because _all_ interior mutability in Rust is built on
// std::cell::UnsafeCell, which has no Copy impl. This impl needs to be
// revisited if that restriction is relaxed in the future.
impl<T: Copy> Copy for ThreadBound<T> {}
impl<T: Copy> Clone for ThreadBound<T> {
fn clone(&self) -> Self {
*self
}
}

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use proc_macro2::{Delimiter, TokenStream, TokenTree};
use std::hash::{Hash, Hasher};
pub(crate) struct TokenTreeHelper<'a>(pub &'a TokenTree);
impl<'a> PartialEq for TokenTreeHelper<'a> {
fn eq(&self, other: &Self) -> bool {
use proc_macro2::Spacing;
match (self.0, other.0) {
(TokenTree::Group(g1), TokenTree::Group(g2)) => {
match (g1.delimiter(), g2.delimiter()) {
(Delimiter::Parenthesis, Delimiter::Parenthesis)
| (Delimiter::Brace, Delimiter::Brace)
| (Delimiter::Bracket, Delimiter::Bracket)
| (Delimiter::None, Delimiter::None) => {}
_ => return false,
}
let s1 = g1.stream().into_iter();
let mut s2 = g2.stream().into_iter();
for item1 in s1 {
let item2 = match s2.next() {
Some(item) => item,
None => return false,
};
if TokenTreeHelper(&item1) != TokenTreeHelper(&item2) {
return false;
}
}
s2.next().is_none()
}
(TokenTree::Punct(o1), TokenTree::Punct(o2)) => {
o1.as_char() == o2.as_char()
&& match (o1.spacing(), o2.spacing()) {
(Spacing::Alone, Spacing::Alone) | (Spacing::Joint, Spacing::Joint) => true,
_ => false,
}
}
(TokenTree::Literal(l1), TokenTree::Literal(l2)) => l1.to_string() == l2.to_string(),
(TokenTree::Ident(s1), TokenTree::Ident(s2)) => s1 == s2,
_ => false,
}
}
}
impl<'a> Hash for TokenTreeHelper<'a> {
fn hash<H: Hasher>(&self, h: &mut H) {
use proc_macro2::Spacing;
match self.0 {
TokenTree::Group(g) => {
0u8.hash(h);
match g.delimiter() {
Delimiter::Parenthesis => 0u8.hash(h),
Delimiter::Brace => 1u8.hash(h),
Delimiter::Bracket => 2u8.hash(h),
Delimiter::None => 3u8.hash(h),
}
for item in g.stream() {
TokenTreeHelper(&item).hash(h);
}
0xFFu8.hash(h); // terminator w/ a variant we don't normally hash
}
TokenTree::Punct(op) => {
1u8.hash(h);
op.as_char().hash(h);
match op.spacing() {
Spacing::Alone => 0u8.hash(h),
Spacing::Joint => 1u8.hash(h),
}
}
TokenTree::Literal(lit) => (2u8, lit.to_string()).hash(h),
TokenTree::Ident(word) => (3u8, word).hash(h),
}
}
}
pub(crate) struct TokenStreamHelper<'a>(pub &'a TokenStream);
impl<'a> PartialEq for TokenStreamHelper<'a> {
fn eq(&self, other: &Self) -> bool {
let left = self.0.clone().into_iter().collect::<Vec<_>>();
let right = other.0.clone().into_iter().collect::<Vec<_>>();
if left.len() != right.len() {
return false;
}
for (a, b) in left.into_iter().zip(right) {
if TokenTreeHelper(&a) != TokenTreeHelper(&b) {
return false;
}
}
true
}
}
impl<'a> Hash for TokenStreamHelper<'a> {
fn hash<H: Hasher>(&self, state: &mut H) {
let tts = self.0.clone().into_iter().collect::<Vec<_>>();
tts.len().hash(state);
for tt in tts {
TokenTreeHelper(&tt).hash(state);
}
}
}

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use crate::parse::ParseStream;
use proc_macro2::{Delimiter, TokenStream};
use std::cmp::Ordering;
use std::iter;
pub(crate) fn between<'a>(begin: ParseStream<'a>, end: ParseStream<'a>) -> TokenStream {
let end = end.cursor();
let mut cursor = begin.cursor();
assert!(crate::buffer::same_buffer(end, cursor));
let mut tokens = TokenStream::new();
while cursor != end {
let (tt, next) = cursor.token_tree().unwrap();
if crate::buffer::cmp_assuming_same_buffer(end, next) == Ordering::Less {
// A syntax node can cross the boundary of a None-delimited group
// due to such groups being transparent to the parser in most cases.
// Any time this occurs the group is known to be semantically
// irrelevant. https://github.com/dtolnay/syn/issues/1235
if let Some((inside, _span, after)) = cursor.group(Delimiter::None) {
assert!(next == after);
cursor = inside;
continue;
} else {
panic!("verbatim end must not be inside a delimited group");
}
}
tokens.extend(iter::once(tt));
cursor = next;
}
tokens
}

65
rust/syn/whitespace.rs Normal file
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@@ -0,0 +1,65 @@
pub(crate) fn skip(mut s: &str) -> &str {
'skip: while !s.is_empty() {
let byte = s.as_bytes()[0];
if byte == b'/' {
if s.starts_with("//")
&& (!s.starts_with("///") || s.starts_with("////"))
&& !s.starts_with("//!")
{
if let Some(i) = s.find('\n') {
s = &s[i + 1..];
continue;
} else {
return "";
}
} else if s.starts_with("/**/") {
s = &s[4..];
continue;
} else if s.starts_with("/*")
&& (!s.starts_with("/**") || s.starts_with("/***"))
&& !s.starts_with("/*!")
{
let mut depth = 0;
let bytes = s.as_bytes();
let mut i = 0;
let upper = bytes.len() - 1;
while i < upper {
if bytes[i] == b'/' && bytes[i + 1] == b'*' {
depth += 1;
i += 1; // eat '*'
} else if bytes[i] == b'*' && bytes[i + 1] == b'/' {
depth -= 1;
if depth == 0 {
s = &s[i + 2..];
continue 'skip;
}
i += 1; // eat '/'
}
i += 1;
}
return s;
}
}
match byte {
b' ' | 0x09..=0x0D => {
s = &s[1..];
continue;
}
b if b <= 0x7F => {}
_ => {
let ch = s.chars().next().unwrap();
if is_whitespace(ch) {
s = &s[ch.len_utf8()..];
continue;
}
}
}
return s;
}
s
}
fn is_whitespace(ch: char) -> bool {
// Rust treats left-to-right mark and right-to-left mark as whitespace
ch.is_whitespace() || ch == '\u{200e}' || ch == '\u{200f}'
}