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use proc_macro2::{Span, TokenNode, TokenStream, TokenTree};
use quote::{ToTokens, Tokens};
use std::cell::Cell;
pub trait Respan {
fn span_for(&self, kind: &TokenNode) -> Span;
fn respan(&self, tt: TokenTree) -> TokenTree {
TokenTree {
span: self.span_for(&tt.kind),
kind: tt.kind,
}
}
}
impl Respan for Span {
fn span_for(&self, _: &TokenNode) -> Span {
*self
}
}
impl<'a, S> Respan for &'a S
where
S: ?Sized + Respan,
{
fn span_for(&self, node: &TokenNode) -> Span {
<S as Respan>::span_for(self, node)
}
}
impl<S> Respan for Box<S>
where
S: ?Sized + Respan,
{
fn span_for(&self, node: &TokenNode) -> Span {
<S as Respan>::span_for(self, node)
}
}
#[derive(Debug, Clone)]
pub struct FirstLast {
first: Cell<Option<Span>>,
last: Span,
}
impl Respan for FirstLast {
fn span_for(&self, _: &TokenNode) -> Span {
self.first.take().unwrap_or(self.last)
}
}
impl FirstLast {
pub fn from_tokens(tokens: &ToTokens) -> Self {
let mut spans = Tokens::new();
tokens.to_tokens(&mut spans);
let good_tokens = TokenStream::from(spans).into_iter().collect::<Vec<_>>();
let first_span = good_tokens
.first()
.map(|t| t.span)
.unwrap_or(Span::def_site());
let last = good_tokens.last().map(|t| t.span).unwrap_or(first_span);
FirstLast {
first: Cell::new(Some(first_span)),
last,
}
}
}