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2021 edition: Unsafe block not detected when accessing a union field inside a closure #87378

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lazytype opened this issue Jul 22, 2021 · 2 comments · Fixed by #87469
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2021 edition: Unsafe block not detected when accessing a union field inside a closure #87378

lazytype opened this issue Jul 22, 2021 · 2 comments · Fixed by #87469
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@arora-aman
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A-edition-2021 Area: The 2021 edition C-bug Category: This is a bug.

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@lazytype
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lazytype commented Jul 22, 2021 •
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Code

I tried this code:

union Union {
    value: u64,
}

fn main() {
    let u = Union { value: 42 };
    
    || {
       unsafe { u.value }
    };
}

I expected to see this happen: no error

Instead, this happened: error[E0133]: access to union field is unsafe and requires unsafe function or block

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=091d060959b30415131533f2e6d93f71

Version it worked on

rustc 1.55.0-nightly 2018 edition
https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=091d060959b30415131533f2e6d93f71

Version with regression

rustc 1.55.0-nightly 2021 edition
https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=091d060959b30415131533f2e6d93f71
@lazytype lazytype added C-bug Category: This is a bug. regression-untriaged Untriaged performance or correctness regression. labels Jul 22, 2021
@rustbot rustbot added the I-prioritize Issue: Indicates that prioritization has been requested for this issue. label Jul 22, 2021
@wesleywiser wesleywiser added the A-edition-2021 Area: The 2021 edition label Jul 22, 2021
@jyn514 jyn514 removed the regression-untriaged Untriaged performance or correctness regression. label Jul 22, 2021
@jyn514 jyn514 changed the title Unsafe block not detected when accessing a union field inside a closure 2021 edition: Unsafe block not detected when accessing a union field inside a closure Jul 22, 2021
@nikomatsakis
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cc @rust-lang/wg-rfc-2229

@arora-aman
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@jyn514 jyn514 removed the I-prioritize Issue: Indicates that prioritization has been requested for this issue. label Jul 23, 2021
@arora-aman arora-aman mentioned this issue Jul 26, 2021
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bors added a commit to rust-lang-ci/rust that referenced this issue Jul 26, 2021
@bors
Auto merge of rust-lang#87469 - sexxi-goose:union, r=nikomatsakis
08095fc 
2229: Don't capture preicese paths on top of a union

- Accessing fields of a union require unsafe block
- As part of 2229 we don't allow precision where we need an unsafe block
to capture.

Fixes: rust-lang#87378

r? `@nikomatsakis`
@bors bors closed this as completed in 75edcd9 Jul 26, 2021
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2229: Don't capture preicese paths on top of a union sexxi-goose/rust
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@nikomatsakis @wesleywiser @lazytype @arora-aman @jyn514 @rustbot