1use crate::error::{Error, Result};
2use proc_macro::{Ident, Span, TokenStream, TokenTree};
3use std::iter;
4
5#[derive(PartialOrd, PartialEq)]
6enum Qualifiers {
7 None,
8 Async,
9 Unsafe,
10 Extern,
11 Abi,
12}
13
14impl Qualifiers {
15 fn from_ident(ident: &Ident) -> Self {
16 match ident.to_string().as_str() {
17 "async" => Qualifiers::Async,
18 "unsafe" => Qualifiers::Unsafe,
19 "extern" => Qualifiers::Extern,
20 _ => Qualifiers::None,
21 }
22 }
23}
24
25pub(crate) fn insert_const(input: TokenStream, const_span: Span) -> Result<TokenStream> {
26 let ref mut input = crate::iter::new(input);
27 let mut out = TokenStream::new();
28 let mut qualifiers = Qualifiers::None;
29 let mut pending = Vec::new();
30
31 while let Some(token) = input.next() {
32 match token {
33 TokenTree::Ident(ref ident) if ident.to_string() == "fn" => {
34 let const_ident = Ident::new("const", const_span);
35 out.extend(iter::once(TokenTree::Ident(const_ident)));
36 out.extend(pending);
37 out.extend(iter::once(token));
38 out.extend(input);
39 return Ok(out);
40 }
41 TokenTree::Ident(ref ident) if Qualifiers::from_ident(ident) > qualifiers => {
42 qualifiers = Qualifiers::from_ident(ident);
43 pending.push(token);
44 }
45 TokenTree::Literal(_) if qualifiers == Qualifiers::Extern => {
46 qualifiers = Qualifiers::Abi;
47 pending.push(token);
48 }
49 _ => {
50 qualifiers = Qualifiers::None;
51 out.extend(pending.drain(..));
52 out.extend(iter::once(token));
53 }
54 }
55 }
56
57 Err(Error::new(const_span, "only allowed on a fn item"))
58}
59