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rust/compiler/rustc_middle
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bors 21fab435da Auto merge of #104844 - cjgillot:mention-eval-place, r=jackh726,RalfJung 
Evaluate place expression in `PlaceMention`

https://github.com/rust-lang/rust/pull/102256 introduces a `PlaceMention(place)` MIR statement which keep trace of `let _ = place` statements from surface rust, but without semantics.

This PR proposes to change the behaviour of `let _ =` patterns with respect to the borrow-checker to verify that the bound place is live.

Specifically, consider this code:
```rust
let _ = {
    let a = 5;
    &a
};
```

This passes borrowck without error on stable. Meanwhile, replacing `_` by `_: _` or `_p` errors with "error[E0597]: `a` does not live long enough", [see playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=c448d25a7c205dc95a0967fe96bccce8).

This PR *does not* change how `_` patterns behave with respect to initializedness: it remains ok to bind a moved-from place to `_`.

The relevant test is `tests/ui/borrowck/let_underscore_temporary.rs`. Crater check found no regression.

For consistency, this PR changes miri to evaluate the place found in `PlaceMention`, and report eventual dangling pointers found within it.

r? `@RalfJung`
2023-04-22 09:54:21 +00:00
..
src Auto merge of #104844 - cjgillot:mention-eval-place, r=jackh726,RalfJung 2023-04-22 09:54:21 +00:00
Cargo.toml Add rustc_fluent_macro to decouple fluent from rustc_macros 2023-04-18 18:56:22 +00:00
messages.ftl fix(middle): emit error rather than delay bug when reaching limit 2023-04-03 11:08:14 +08:00
README.md

README.md

For more information about how rustc works, see the rustc dev guide.