Tuple indexing regression · Issue #59553 · rust-lang/rust (original) (raw)

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Description

#59421 breaks some code generated by proc macros because quote converts integer to a tokenstream with a suffix.

Proc macro:

extern crate proc_macro; use proc_macro::TokenStream; use quote::quote;

#[proc_macro] pub fn foo(_: TokenStream) -> TokenStream { let index = 0; TokenStream::from(quote! { struct Foo(()); fn bar() { let x = Foo(()); x.#index } }) }

Calling code:

Error:

error: suffixes on a tuple index are invalid
 --> src\lib.rs:3:1
  |
3 | foo!();
  | ^^^^^^^ invalid suffix `i32`

It can be avoided by using syn::Index::from or proc_macro::Literal::*_unsuffixed.

I have already fixed my library (taiki-e/pin-project@5f5cc35), but it can happen elsewhere.