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deref patterns: impl DerefPure for more std types #123480

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merged 1 commit into from
May 3, 2024

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Context: deref patterns. The requirements of DerefPure aren't precise yet, but these types unambiguously satisfy them.

Interestingly, a hypothetical impl DerefMut for Cow that does a Clone would not be eligible for DerefPure if we allow mixing deref patterns with normal patterns. If the following is exhaustive then the DerefMut would cause UB:

match &mut Cow::Borrowed(&()) {
    Cow::Owned(_) => ..., // Doesn't match
    deref!(_x) if false => ..., // Causes the variant to switch to `Owned`
    Cow::Borrowed(_) => ..., // Doesn't match
    // We reach unreachable
}

@Nadrieril Nadrieril added the F-deref_patterns `#![feature(deref_patterns)]` label Apr 4, 2024
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r? @m-ou-se

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@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Apr 4, 2024
@Nadrieril Nadrieril mentioned this pull request Apr 4, 2024
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r? @compiler-errors

@rustbot rustbot assigned compiler-errors and unassigned m-ou-se May 2, 2024
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@bors r+

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bors commented May 3, 2024

📌 Commit 1a83bea has been approved by compiler-errors

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 3, 2024
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@bors rollup

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bors added a commit to rust-lang-ci/rust that referenced this pull request May 3, 2024
…iaskrgr

Rollup of 10 pull requests

Successful merges:

 - rust-lang#123480 (deref patterns: impl `DerefPure` for more std types)
 - rust-lang#124412 (io safety: update Unix explanation to use `Arc`)
 - rust-lang#124441 (String.truncate comment microfix (greater or equal))
 - rust-lang#124594 (run-make-support: preserve tooks.mk behavior for EXTRACXXFLAGS)
 - rust-lang#124604 (library/std: Remove unused `gimli-symbolize` feature)
 - rust-lang#124607 (`rustc_expand` cleanups)
 - rust-lang#124609 (variable-precision float operations can differ depending on optimization levels)
 - rust-lang#124610 (Tweak `consts_may_unify`)
 - rust-lang#124626 (const_eval_select: add tracking issue)
 - rust-lang#124637 (AST pretty: Use `builtin_syntax` for type ascription)

Failed merges:

 - rust-lang#124638 (Move some tests from `rustc_expand` to `rustc_parse`.)

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit e17a222 into rust-lang:master May 3, 2024
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@rustbot rustbot added this to the 1.80.0 milestone May 3, 2024
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request May 3, 2024
Rollup merge of rust-lang#123480 - Nadrieril:impl-all-derefpures, r=compiler-errors

deref patterns: impl `DerefPure` for more std types

Context: [deref patterns](rust-lang#87121). The requirements of `DerefPure` aren't precise yet, but these types unambiguously satisfy them.

Interestingly, a hypothetical `impl DerefMut for Cow` that does a `Clone` would *not* be eligible for `DerefPure` if we allow mixing deref patterns with normal patterns. If the following is exhaustive then the `DerefMut` would cause UB:
```rust
match &mut Cow::Borrowed(&()) {
    Cow::Owned(_) => ..., // Doesn't match
    deref!(_x) if false => ..., // Causes the variant to switch to `Owned`
    Cow::Borrowed(_) => ..., // Doesn't match
    // We reach unreachable
}
```
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RalfJung commented May 3, 2024

@bors r-

@bors bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels May 3, 2024
@Nadrieril Nadrieril deleted the impl-all-derefpures branch May 4, 2024 14:21
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6 participants