E0205 needs to be updated to new format

[sophiajt]

From: src/test/compile-fail/E0205.rs

Error E0205 needs a span label and updated title, changing it from:

error[E0205]: the trait `Copy` may not be implemented for this type; variant `Bar` does not implement `Copy`
  --> src/test/compile-fail/E0205.rs:18:10
   |
18 | #[derive(Copy)] //~ ERROR E0205
   |          ^^^^
src/test/compile-fail/E0205.rs:18:10: 18:14 note: in this expansion of #[derive(Copy)] (defined in src/test/compile-fail/E0205.rs)

error[E0205]: the trait `Copy` may not be implemented for this type; variant `Bar` does not implement `Copy`
  --> src/test/compile-fail/E0205.rs:16:1
   |
16 | impl Copy for Foo { } //~ ERROR E0205
   | ^^^^^^^^^^^^^^^^^^^^^

to:

error[E0205]: the trait `Copy` may not be implemented for this type
  --> src/test/compile-fail/E0205.rs:18:10
   |
18 | #[derive(Copy)] //~ ERROR E0205
   |          ^^^^ variant `Bar` does not implement `Copy`
src/test/compile-fail/E0205.rs:18:10: 18:14 note: in this expansion of #[derive(Copy)] (defined in src/test/compile-fail/E0205.rs)

error[E0205]: the trait `Copy` may not be implemented for this type
  --> src/test/compile-fail/E0205.rs:16:1
   |
16 | impl Copy for Foo { } //~ ERROR E0205
   | ^^^^^^^^^^^^^^^^^^^^^ variant `Bar` does not implement `Copy`

Bonus: the span for the second one could be shrunk to just the Copy part:

error[E0205]: the trait `Copy` may not be implemented for this type
  --> src/test/compile-fail/E0205.rs:18:10
   |
18 | #[derive(Copy)] //~ ERROR E0205
   |          ^^^^ variant `Bar` does not implement `Copy`
src/test/compile-fail/E0205.rs:18:10: 18:14 note: in this expansion of #[derive(Copy)] (defined in src/test/compile-fail/E0205.rs)

error[E0205]: the trait `Copy` may not be implemented for this type
  --> src/test/compile-fail/E0205.rs:16:1
   |
16 | impl Copy for Foo { } //~ ERROR E0205
   |      ^^^^ variant `Bar` does not implement `Copy`

Note: I'm not sure the "expansion of..." part is helpful, you could also remove that.

Seems related to #35381

[KiChjang]

@munyari Are you still working on the bonus part for this issue? Otherwise I can take over.

[munyari]

Feel free to take them both @KiChjang

[KiChjang]

I'm not quite in favour of removing the "in the expansion of" note. This is produced in librustc_errors/emitter.rs, and it is called when there is an error in macro invocation. #[derive(Copy)] is a special case, since the attribute expands into a macro. I'm not too keen on adding additional logic in emitter.rs just to handle this special case. Compiler plugins may also use macro invocations in attributes, so it's best to leave it alone.

[sophiajt]

@KiChjang - +1 on not making it special logic. There's a separate thread on improving macro errors. This should let us fix them more completely.