Suggest removing parenthesis surrounding lifetimes

[estebank]

Given:

trait Trait {}
fn f<'a, T: Trait + ('a)>() {}

suggest the correct syntax

error: parenthesized lifetime bounds are not supported
  --> $DIR/trait-object-lifetime-parens.rs:5:24
   |
LL | fn f<'a, T: Trait + ('a)>() {}
   |                        ^
help: remove the braces
   |
LL | fn f<'a, T: Trait + 'a>() {}
   |                     ^^

[igorsdv]

I'd like to work on this (I'm new)

[estebank]

@goldenlentils feel free to reach out for any help you might need! And take a look at The Forge, particularly the explanation on how to run tests (./x.py test src/test/ui --stage 1 --bless is what I normally run).

You will find the code that emits this error in parse_generic_bounds_common in libsyntax/parse/parser.rs. You will need to change the span_err call for an struct_span_err that will give you a DiagnosticBuilder that you can modify using span_suggestion_with_applicability. You can search the codebase (and the same file) for how to use it.

[igorsdv]

@estebank Thanks!

I managed to get the error to look like this:

error: parenthesized lifetime bounds are not supported
 --> /home/igor/dev/sandbox/sample.rs:3:21
  |
3 | fn f<'a, T: Trait + ('a)>() {}
  |                     ^^^^ help: remove the parentheses: `'a`

error: aborting due to previous error

Or, if using span_suggestion_short_with_applicability:

error: parenthesized lifetime bounds are not supported
 --> /home/igor/dev/sandbox/sample.rs:3:21
  |
3 | fn f<'a, T: Trait + ('a)>() {}
  |                     ^^^^ help: remove the parentheses

error: aborting due to previous error

As I understand, the help message appears inline because of the condition sugg.msg.split_whitespace().count() < 10 at librustc_errors/emitter.rs:46. Is this fine? Is any of the two options above preferable?

[estebank]

@igorsdv your understanding is correct. Being inline is fine and I'm partial towards the short version, at least in this case.