non-exhaustive patterns false positive

[leonardo-m]

fn foo(x: usize) -> u32 {
    match x {
        0 ..= usize::MAX => 0
    }
}
fn main() {}

Gives:

error[E0004]: non-exhaustive patterns: `_` not covered
 --> ...\test.rs:2:11
  |
2 |     match x {
  |           ^ pattern `_` not covered
  |
  = help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
  = note: the matched value is of type `usize`

[jonas-schievink]

Fairly sure this is intentional for usize

[leonardo-m]

From the pull 73937 I've seen a part that I didn't see/remember:

An unstable feature precise_pointer_size_matching will be added to permit matching exactly on pointer-size integer types.

So you're right, this isn't a new bug, it's a known unfinished part. I hope to see that precise_pointer_size_matching implemented.

[varkor]

I hope to see that precise_pointer_size_matching implemented.

It already exists.

[leonardo-m]

I see, then what do I have to hope to see? :-)

[varkor]

I'm not sure the feature is ever going to be stabilised, because there are concerns that this isn't a desirable feature. But hopefully the diagnostics will at least be improved in #73937.

[leonardo-m]

Do you have a link to such concerns? (Or are you willing to summarize them?)
(I value your work on the compiler a lot varkor :-) )

[varkor]

I think the relevant concerns arose in the RFC thread (from this comment up). The overview is that we ought not to make assumptions about pointer sizes on the target platform, because they're not guaranteed to be fixed, so this could cause compatibility issues.