Second panicking custom derive has bad span

[alexcrichton]

Inlined from #35900 (comment)

---

Another issue. If a struct has two different custom derives on it and the second one panics, the error span will point to the first one, not the one which panicked.

Reproduction Script

[alexcrichton]

@sgrif was "Reproduction Script" supposed to be a link? I'm spinning this off from #35900 (comment) as I don't think it's going to block stabilization and/or closing that issue.

[sgrif]

Reproduction script there is a summary tag

[sgrif]

Reproduction Script

In a crate called demo_plugin

#![feature(rustc_macro, rustc_macro_lib)]

extern crate rustc_macro;

use rustc_macro::TokenStream;

#[rustc_macro_derive(Foo)]
pub fn derive_foo(input: TokenStream) -> TokenStream {
    input
}

#[rustc_macro_derive(Bar)]
pub fn derive_bar(input: TokenStream) -> TokenStream {
    panic!("lolnope");
}

In another crate

#![feature(rustc_macro)]

#[macro_use] extern crate demo_plugin;

#[derive(Foo, Bar)]
struct Baz {
    a: i32,
    b: i32,
}

The error will highlight Foo even though Bar panicked.

[keeperofdakeys]

This seems to be fixed now, so this issue can be closed.

[keeperofdakeys]

I ran this as a test, and got the following output:

   Compiling b v0.1.0 (file:///tmp/b)
error: custom derive attribute panicked
 --> src/lib.rs:5:15
  |
5 | #[derive(Foo, Bar)]
  |               ^^^
  |
  = help: message: lolnope

error: Could not compile `b`.