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Constants, slice patterns, and exhaustiveness interact in suboptimal ways #65413

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Constants, slice patterns, and exhaustiveness interact in suboptimal ways#65413
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Nadrieril
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A-const-evalArea: Constant evaluation, covers all const contexts (static, const fn, ...)A-slice-patternsArea: Slice patterns, https://github.com/rust-lang/rust/issues/23121C-bugCategory: This is a bug.F-slice_patterns`#![feature(slice_patterns)]`T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.requires-nightlyThis issue requires a nightly compiler in some way. When possible, use a F-* label instead.

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@arielb1
arielb1
opened on Oct 14, 2019

For example,

#![feature(slice_patterns)]

const C0: &'static [u8] = b"\x00";

fn main() {
   let x: &[u8] = &[0];
   match x { // this code compiles
       &[] => {},
       &[1..=255] => {},
       C0 => {}, //~ unreachable pattern (no it's not)
       &[_, _, ..] => {}
   }
}

cc @oli-obk

Activity

  1. varkor commented on Oct 14, 2019

    @varkor
    varkor
    on Oct 14, 2019
    Contributor

    Probably related to #53708: consts are mishandled at the moment.

  2. jonas-schievink
    added
    A-const-evalArea: Constant evaluation, covers all const contexts (static, const fn, ...)
    A-slice-patternsArea: Slice patterns, https://github.com/rust-lang/rust/issues/23121
    C-bugCategory: This is a bug.
    F-slice_patterns`#![feature(slice_patterns)]`
    requires-nightlyThis issue requires a nightly compiler in some way. When possible, use a F-* label instead.
    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.
    on Oct 14, 2019

  3. Centril commented on Nov 17, 2019

    @Centril
    Centril
    on Nov 17, 2019
    Contributor

    Reduced:

    #![feature(slice_patterns)]

fn main() {
   let x: &[u8] = &[0];
   match x { // this code compiles
       &[] => {},
       &[1..=255] => {},
       b"\x00" => {}, //~ unreachable pattern (no it's not)
       &[_, _, ..] => {}
   }
}

  4. Nadrieril commented on Nov 17, 2019

    @Nadrieril
    Nadrieril
    on Nov 17, 2019
    Member

    I found a fix, I'll make a PR once #66497 gets merged

  5. Centril
    assigned
    Nadrieril
    on Nov 17, 2019
  6. bors
    added a commit that references this issue on Nov 28, 2019

    Auto merge of #66603 - Nadrieril:fix-65413, r=varkor

    f453d11
  7. bors
    closed this as completedin f453d11on Nov 28, 2019
  8. tmandry
    added a commit that references this issue on Jan 18, 2020

    Rollup merge of rust-lang#67712 - Centril:stabilize-slice_patterns, r…

    a4014b6
  9. Centril
    added a commit that references this issue on Jan 18, 2020

    Rollup merge of rust-lang#67712 - Centril:stabilize-slice_patterns, r…

    733c7f4
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A-const-evalArea: Constant evaluation, covers all const contexts (static, const fn, ...)A-slice-patternsArea: Slice patterns, https://github.com/rust-lang/rust/issues/23121C-bugCategory: This is a bug.F-slice_patterns`#![feature(slice_patterns)]`T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.requires-nightlyThis issue requires a nightly compiler in some way. When possible, use a F-* label instead.

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