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Implement MIR lowering for unsafe binders #130514

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Implement MIR lowering for unsafe binders #130514

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@compiler-errors compiler-errors commented Sep 18, 2024 •
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This is the final bit of the unsafe binders puzzle. It implement MIR and drop semantics for unsafe binders.

Namely, unsafe binders are implemented as a MIR projection.

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@rustbot rustbot added PG-exploit-mitigations Project group: Exploit mitigations S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. WG-trait-system-refactor The Rustc Trait System Refactor Initiative (-Znext-solver) labels Sep 18, 2024
@compiler-errors compiler-errors changed the title Initial implementation of unsafe binders Initial implementation of unsafe binder types Sep 18, 2024
@traviscross traviscross mentioned this pull request Sep 18, 2024
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@rustbot rustbot added the A-rustdoc-json Area: Rustdoc JSON backend label Sep 18, 2024
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@compiler-errors compiler-errors mentioned this pull request Sep 18, 2024
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bors commented Sep 23, 2024

☔ The latest upstream changes (presumably #130724) made this pull request unmergeable. Please resolve the merge conflicts.

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bors commented Sep 24, 2024

☔ The latest upstream changes (presumably #127117) made this pull request unmergeable. Please resolve the merge conflicts.

@Dylan-DPC Dylan-DPC added S-experimental Status: Ongoing experiment that does not require reviewing and won't be merged in its current state. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 20, 2024
@compiler-errors compiler-errors mentioned this pull request Dec 10, 2024
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matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Dec 13, 2024
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Rollup merge of rust-lang#134140 - compiler-errors:unsafe-binders-ast…
5c9b227 
…, r=oli-obk

Add AST support for unsafe binders

I'm splitting up rust-lang#130514 into pieces. It's impossible for me to keep up with a huge PR like that. I'll land type system support for this next, probably w/o MIR lowering, which will come later.

r? `@oli-obk`
cc `@BoxyUwU` and `@lcnr` who also may want to look at this, though this PR doesn't do too much yet
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Dec 14, 2024
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Unrolled build for rust-lang#134140
52edea8 
Rollup merge of rust-lang#134140 - compiler-errors:unsafe-binders-ast, r=oli-obk

Add AST support for unsafe binders

I'm splitting up rust-lang#130514 into pieces. It's impossible for me to keep up with a huge PR like that. I'll land type system support for this next, probably w/o MIR lowering, which will come later.

r? `@oli-obk`
cc `@BoxyUwU` and `@lcnr` who also may want to look at this, though this PR doesn't do too much yet
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flip1995 pushed a commit to flip1995/rust that referenced this pull request Dec 15, 2024
@matthiaskrgr
Rollup merge of rust-lang#134140 - compiler-errors:unsafe-binders-ast…
9ce2645 
…, r=oli-obk

Add AST support for unsafe binders

I'm splitting up rust-lang#130514 into pieces. It's impossible for me to keep up with a huge PR like that. I'll land type system support for this next, probably w/o MIR lowering, which will come later.

r? `@oli-obk`
cc `@BoxyUwU` and `@lcnr` who also may want to look at this, though this PR doesn't do too much yet
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bors commented Dec 17, 2024

☔ The latest upstream changes (presumably #134414) made this pull request unmergeable. Please resolve the merge conflicts.

@bors bors added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Dec 17, 2024
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bors commented Dec 22, 2024

☔ The latest upstream changes (presumably #134326) made this pull request unmergeable. Please resolve the merge conflicts.

@compiler-errors compiler-errors changed the title Initial implementation of unsafe binder types Implement MIR lowering for unsafe binders Jan 6, 2025
scottmcm
scottmcm reviewed Jan 9, 2025
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compiler/rustc_middle/src/mir/statement.rs
Comment on lines +108 to +109
// FIXME(unsafe_binders): Figure this out.
Self::UnsafeBinderCast(..) => false,
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My guess would be that since lifetimes are mono'd away, this is "allowed" in debug info because it's a no-op for the actual value?

Definitely don't trust me on that, though -- I know almost nothing about debug info.

scottmcm
scottmcm reviewed Jan 9, 2025
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compiler/rustc_mir_build/messages.ftl
Comment on lines +376 to +377
.note = casting to or from an `unsafe<...>` binder type is unsafe since it erases lifetime
information that may be required to uphold safety guarantees of a type
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curiosity: I'm surprised that Foo<'specific> to unsafe<'a> Foo<'a> is unsafe.

Replacing the existential lifetime with a specific one is obviously unsafe to me, but I would have expected that "erasing" it was fine.

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When you cast something to an unsafe binder, you no longer require that casted region to be live (see: liveness), since it's erased. This certainly has implications on things like drop and other built-in impls of the type.

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