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Break out of the correct number of scopes in loops #62388

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merged 1 commit into from
Jul 5, 2019

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matthewjasper
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We were incorrectly breaking out of one too many drop scopes when
generating MIR for loops and breakable blocks, resulting in use after
free and associated borrow checker warnings.

This wasn't noticed because the scope that we're breaking out of twice
is only used for temporaries that are created for adjustments applied to
the loop. Since loops generally propagate coercions to the break
expressions, the only case we see this is when the type of the loop is a
smart pointer to a trait object.

Closes #62312

We were incorrectly breaking out of one too many drop scopes when
generating MIR for loops and breakable blocks, resulting in use after
free and associated borrow checker warnings.

This wasn't noticed because the scope that we're breaking out of twice
is only used for temporaries that are created for adjustments applied to
the loop. Since loops generally propagate coercions to the `break`
expressions, the only case we see this is when the type of the loop is a
smart pointer to a trait object.
@rust-highfive
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r? @petrochenkov

(rust_highfive has picked a reviewer for you, use r? to override)

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 4, 2019
@petrochenkov
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I know very little about MIR.
r? @rust-lang/compiler

@eddyb
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eddyb commented Jul 5, 2019

r? @eddyb
@bors r+

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bors commented Jul 5, 2019

📌 Commit 1b7ffe5 has been approved by eddyb

@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 Jul 5, 2019
Centril added a commit to Centril/rust that referenced this pull request Jul 5, 2019
…tion, r=eddyb

Break out of the correct number of scopes in loops

We were incorrectly breaking out of one too many drop scopes when
generating MIR for loops and breakable blocks, resulting in use after
free and associated borrow checker warnings.

This wasn't noticed because the scope that we're breaking out of twice
is only used for temporaries that are created for adjustments applied to
the loop. Since loops generally propagate coercions to the `break`
expressions, the only case we see this is when the type of the loop is a
smart pointer to a trait object.

Closes rust-lang#62312
bors added a commit that referenced this pull request Jul 5, 2019
Rollup of 10 pull requests

Successful merges:

 - #62123 ( Remove needless lifetimes (std))
 - #62150 (Implement mem::{zeroed,uninitialized} in terms of MaybeUninit.)
 - #62169 (Derive which queries to save using the proc macro)
 - #62238 (Fix code block information icon position)
 - #62292 (Move `async || ...` closures into `#![feature(async_closure)]`)
 - #62323 (Clarify unaligned fields in ptr::{read,write}_unaligned)
 - #62324 (Reduce reliance on `await!(...)` macro)
 - #62371 (Add tracking issue for Box::into_pin)
 - #62383 (Improve error span for async type inference error)
 - #62388 (Break out of the correct number of scopes in loops)

Failed merges:

r? @ghost
@bors bors merged commit 1b7ffe5 into master Jul 5, 2019
@matthewjasper matthewjasper deleted the fix-loop-break-mir-generation branch July 5, 2019 15:55
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Future compat warning with .awaiting a BoxFuture
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