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use crate::error::{Error, Result};
use proc_macro::token_stream::IntoIter as TokenIter;
use proc_macro::{Spacing, Span, TokenStream, TokenTree};
use std::iter;
pub struct Expr(TokenStream);
pub fn parse(input: &mut TokenIter) -> Result<Expr> {
#[derive(PartialEq)]
enum Lookbehind {
JointColon,
DoubleColon,
Other,
}
let mut expr = TokenStream::new();
let mut lookbehind = Lookbehind::Other;
let mut angle_bracket_depth = 0;
loop {
match input.next() {
Some(TokenTree::Punct(punct)) => {
let ch = punct.as_char();
let spacing = punct.spacing();
expr.extend(iter::once(TokenTree::Punct(punct)));
lookbehind = match ch {
',' if angle_bracket_depth == 0 => return Ok(Expr(expr)),
':' if lookbehind == Lookbehind::JointColon => Lookbehind::DoubleColon,
':' if spacing == Spacing::Joint => Lookbehind::JointColon,
'<' if lookbehind == Lookbehind::DoubleColon => {
angle_bracket_depth += 1;
Lookbehind::Other
}
'>' if angle_bracket_depth > 0 => {
angle_bracket_depth -= 1;
Lookbehind::Other
}
_ => Lookbehind::Other,
};
}
Some(token) => expr.extend(iter::once(token)),
None => {
return Err(Error::new(
Span::call_site(),
"unexpected end of macro input",
))
}
}
}
}
impl Expr {
pub fn into_tokens(self) -> TokenStream {
self.0
}
}
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