| 1 | use crate::error::{Error, Result}; |
|---|---|
| 2 | use proc_macro::{Ident, Span, TokenStream, TokenTree}; |
| 3 | use std::iter; |
| 4 | |
| 5 | #[derive(PartialOrd, PartialEq)] |
| 6 | enum Qualifiers { |
| 7 | None, |
| 8 | Async, |
| 9 | Unsafe, |
| 10 | Extern, |
| 11 | Abi, |
| 12 | } |
| 13 | |
| 14 | impl 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 | |
| 25 | pub(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 |