//! 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 parse::{ParseStream, Result};
#[cfg(syn_can_use_associated_constants)]
use buffer::Cursor;
#[cfg(syn_can_use_associated_constants)]
use parse::Peek;
#[cfg(syn_can_use_associated_constants)]
use sealed::lookahead;
#[cfg(syn_can_use_associated_constants)]
use 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
///
/// ```edition2018
/// 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.
#[cfg(syn_can_use_associated_constants)]
#[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`.
///
/// ```edition2018
/// 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()
}
}
}
#[cfg(syn_can_use_associated_constants)]
impl Peek for private::PeekFn {
type Token = private::IdentAny;
}
#[cfg(syn_can_use_associated_constants)]
impl CustomToken for private::IdentAny {
fn peek(cursor: Cursor) -> bool {
cursor.ident().is_some()
}
fn display() -> &'static str {
"identifier"
}
}
#[cfg(syn_can_use_associated_constants)]
impl lookahead::Sealed for private::PeekFn {}
mod private {
use proc_macro2::Ident;
pub trait Sealed {}
impl Sealed for Ident {}
#[cfg(syn_can_use_associated_constants)]
#[derive(Copy, Clone)]
pub struct PeekFn;
#[cfg(syn_can_use_associated_constants)]
pub struct IdentAny;
}