1 files changed, 135 insertions, 0 deletions
diff --git a/syn/src/ext.rs b/syn/src/ext.rs
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+//! Extension traits to provide parsing methods on foreign types.
+//!
+//! *This module is available if Syn is built with the `"parsing"` feature.*
+
+use proc_macro2::Ident;
+
+use crate::parse::{ParseStream, Result};
+
+use crate::buffer::Cursor;
+use crate::parse::Peek;
+use crate::sealed::lookahead;
+use crate::token::CustomToken;
+
+/// 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`.
+///
+/// *This trait is available if Syn is built with the `"parsing"` feature.*
+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 string.starts_with("r#") {
+            Ident::new(&string[2..], 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 {}
+
+    #[derive(Copy, Clone)]
+    pub struct PeekFn;
+    pub struct IdentAny;
+}