Unused function warnings should return a span of only the function name

[jackmott]

Currently a warning for an unused function returns a span of the entire function. As a consequence, RLS based IDE environments may then put green squiggles on the entire function. This makes it very annoying to work on a function, if you have not yet written the function that uses it.

There may be other unused warnings for structs/traits that could be similarly adjusted.

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

[sanxiyn]

Does it? For me warnings for unused functions only return span of function signatures, not bodies. Is that still annoying? Same for structs.

I think this is somewhat intentional as it is the item that is unused. Spanning the name usually means name resolution failure.

[jackmott]

VSCode ends up highlighting the whole function, so if you are correct this bug should be closed and moved to that repo. How can we verify?

[sanxiyn]

It would help if you could provide a test case that reproduces the bug, preferably in the following format:

$ cat test.rs
fn f() { /* not in span */ }
fn main() {}
$ rustc test.rs
warning: function is never used: `f`
 --> test.rs:1:1
  |
1 | fn f() { /* not in span */ }
  | ^^^^^^
  |
  = note: #[warn(dead_code)] on by default

[estebank]

Some further details in duplicate #63064

[estebank]

Still reproduces.

[Quantumplation]

@rustbot claim

I'd like to pick this up as my first contribution. @jakubadamw had said (on the duplicate) that he intended to work on this, but it's been a few months, so I'm not sure if he's lost interest or not.

I started to work on this, and I figured first step would be to write a ui test for it. I notice that by now there's a few dead-code related tests. Is there a policy around moving tests to sub folders? If no one objects, I'd like to move all the dead-code related tests to a dead-code subfolder as part of this work as well.

[jackmott]

@Quantumplation I can't speak for the rust maintainers but generally it is greatly preferred to just have one thing per PR. I would do the test organization as a separate pr.

[estebank]

@Quantumplation go for it, in separate commits in the same PR.