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Improve and fix diagnostics of exhaustiveness checking

 3 years ago
source link: https://github.com/rust-lang/rust/pull/80104
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Contributor

Nadrieril commented 13 days ago •

edited

Primarily, this fixes #56379. This also fixes incorrect interactions between or-patterns and slice patterns that I discovered while working on #56379. Those two examples show the incorrect diagnostics:

match &[][..] {
    [true] => {}
    [true // detected as unreachable but that's not true
        | false, ..] => {}
    _ => {}
}
match (true, None) {
    (true, Some(_)) => {}
    (false, Some(true)) => {}
    (true | false, None | Some(true // should be detected as unreachable
                               | false)) => {}
}

I did not measure any perf impact. However, I suspect that 616ba9f should have a negative impact on large or-patterns. I'll see what the perf run says; I have optimization ideas up my sleeve if needed.

EDIT: I initially had a noticeable perf impact that I thought unavoidable. I then proceeded to avoid it x)

r? @varkor
@rustbot label +A-exhaustiveness-checking


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