No unnecessary parentheses warning in types

[oli-cosmian]

Types can be parenthesized, which is useful for e.g. dyn (Foo + 'static) or similar, but often these parentheses are unnecessary. Whenever a trivial type is parenthesized the compiler should suggest to remove the parentheses

pub fn foo() -> (i32) { 42 }

(Playground)

Errors:

   Compiling playground v0.0.1 (/playground)
    Finished dev [unoptimized + debuginfo] target(s) in 0.64s

This issue has been assigned to @sjmann via this comment.

[Centril]

I think this falls under the spirit of the unused_parens lint and the language team does not need to approve this as I think it is obviously right.

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Mentoring instructions:

See #64128 for a PR that recently changed the semantics of the unused_parens lint. You'll want to introduce fn check_ty and then match on the ty.node: TyKind while keeping in mind to avoid suggesting the removal of parenthesis that would result in a compilation error.

[sjmann]

Would it be ok if I try to tackle this as a first time contributor? Seems like a nice starter issue.

[Centril]

@sjmann sure, go right ahead!

@rustbot assign @sjmann

[ijt]

@sjmann, are you still working on this?

[jack-t]

Hi —

I've got what I believe is a working PR over here. There's a kind of chicken-and-egg problem with building core with the lint, though. I'm not totally sure how to solve it.

Thanks!