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use alloc::borrow::Cow;
use core::fmt;
use proc_macro2::{Ident, Span};
/// Specialized formatting trait used by `format_ident!`.
///
/// [`Ident`] arguments formatted using this trait will have their `r#` prefix
/// stripped, if present.
///
/// See [`format_ident!`] for more information.
///
/// [`format_ident!`]: crate::format_ident
pub trait IdentFragment {
/// Format this value as an identifier fragment.
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result;
/// Span associated with this `IdentFragment`.
///
/// If non-`None`, may be inherited by formatted identifiers.
fn span(&self) -> Option<Span> {
None
}
}
impl<T: IdentFragment + ?Sized> IdentFragment for &T {
fn span(&self) -> Option<Span> {
<T as IdentFragment>::span(*self)
}
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
IdentFragment::fmt(*self, f)
}
}
impl<T: IdentFragment + ?Sized> IdentFragment for &mut T {
fn span(&self) -> Option<Span> {
<T as IdentFragment>::span(*self)
}
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
IdentFragment::fmt(*self, f)
}
}
impl IdentFragment for Ident {
fn span(&self) -> Option<Span> {
Some(self.span())
}
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let id = self.to_string();
if let Some(id) = id.strip_prefix("r#") {
fmt::Display::fmt(id, f)
} else {
fmt::Display::fmt(&id[..], f)
}
}
}
impl<T> IdentFragment for Cow<'_, T>
where
T: IdentFragment + ToOwned + ?Sized,
{
fn span(&self) -> Option<Span> {
T::span(self)
}
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
T::fmt(self, f)
}
}
// Limited set of types which this is implemented for, as we want to avoid types
// which will often include non-identifier characters in their `Display` impl.
macro_rules! ident_fragment_display {
($($T:ty),*) => {
$(
impl IdentFragment for $T {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Display::fmt(self, f)
}
}
)*
};
}
ident_fragment_display!(bool, str, String, char);
ident_fragment_display!(u8, u16, u32, u64, u128, usize);