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use crate::error::{Error, Result};
use proc_macro::{Ident, Span, TokenStream, TokenTree};
use std::iter;
#[derive(PartialOrd, PartialEq)]
enum Qualifiers {
None,
Async,
Unsafe,
Extern,
Abi,
}
impl Qualifiers {
fn from_ident(ident: &Ident) -> Self {
match ident.to_string().as_str() {
"async" => Qualifiers::Async,
"unsafe" => Qualifiers::Unsafe,
"extern" => Qualifiers::Extern,
_ => Qualifiers::None,
}
}
}
pub(crate) fn insert_const(input: TokenStream, const_span: Span) -> Result<TokenStream> {
let ref mut input = crate::iter::new(input);
let mut out = TokenStream::new();
let mut qualifiers = Qualifiers::None;
let mut pending = Vec::new();
while let Some(token) = input.next() {
match token {
TokenTree::Ident(ref ident) if ident.to_string() == "fn" => {
let const_ident = Ident::new("const", const_span);
out.extend(iter::once(TokenTree::Ident(const_ident)));
out.extend(pending);
out.extend(iter::once(token));
out.extend(input);
return Ok(out);
}
TokenTree::Ident(ref ident) if Qualifiers::from_ident(ident) > qualifiers => {
qualifiers = Qualifiers::from_ident(ident);
pending.push(token);
}
TokenTree::Literal(_) if qualifiers == Qualifiers::Extern => {
qualifiers = Qualifiers::Abi;
pending.push(token);
}
_ => {
qualifiers = Qualifiers::None;
out.extend(pending.drain(..));
out.extend(iter::once(token));
}
}
}
Err(Error::new(const_span, "only allowed on a fn item"))
}
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