21fab435da
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` |
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