Point at type parameter in plain path expr

[compiler-errors]

Slightly better error message for a kinda unique use case.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @spastorino (or someone else) soon.

Please see the contribution instructions for more information.

[spastorino]

@compiler-errors looks good but, what was happening before this PR?

[compiler-errors]

If you test the UI test on nightly:

fn foo<T: std::fmt::Display>() {}

fn main() {
    let x = foo::<()>;
    //~^ ERROR `()` doesn't implement `std::fmt::Display`
}

Then you see:

error[[E0277]](https://doc.rust-lang.org/nightly/error-index.html#E0277): `()` doesn't implement `std::fmt::Display`
 --> src/main.rs:4:13
  |
4 |     let x = foo::<()>;
  |             ^^^^^^^^^ `()` cannot be formatted with the default formatter
  |
  = help: the trait `std::fmt::Display` is not implemented for `()`
  = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
note: required by a bound in `foo`
 --> src/main.rs:1:11
  |
1 | fn foo<T: std::fmt::Display>() {}
  |           ^^^^^^^^^^^^^^^^^ required by this bound in `foo`

Notably, that error message on line 4 becomes (after this PR):

LL |     let x = foo::<()>;
   |                   ^^ `()` cannot be formatted with the default formatter

Notice the tighter span.

This was because we were only triggering point_at_path_if_possible if the ExprKind::Path had a parent of ExprKind::Call, even though that's only really necessary to point at args. We can point to the path regardless.

[spastorino]

@bors r+ rollup

[bors]

📌 Commit 3b3c706 has been approved by spastorino

It is now in the queue for this repository.