A syntax error loses the span

[antoyo]

Hi.
There's a reproducer for this bug here.

When there is a syntax error, the span info is lost and that makes output errors like this:

 --> src/main.rs:8:1
  |
8 | #[hello_macro_derive]
  | ^^^^^^^^^^^^^^^^^^^^^
  | |
  | expected `i32`, found struct `std::string::String`
  | expected due to this

Thanks to fix the issue.

[mystor]

This appears to be an instance of the compiler bug rust-lang/rust#43081, rather than being a bug in syn.

[dtolnay]

Yeah this is rust-lang/rust#43081. If you insert println!("{:#?}", input) as the first line of hello_macro_derive you'll see that the spans all come in as #0 bytes(0..0) so it isn't syn losing them.

[Aaron1011]

The specific issue is tracked by rust-lang/rust#75734