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Auto merge of #107251 - dingxiangfei2009:let-chain-rescope, r=jieyouxu

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Rescope temp lifetime in if-let into IfElse with migration lint

Tracking issue #124085

This PR shortens the temporary lifetime to cover only the pattern matching and consequent branch of a `if let`.

At the expression location, means that the lifetime is shortened from previously the deepest enclosing block or statement in Edition 2021. This warrants an Edition change.

Coming with the Edition change, this patch also implements an edition lint to warn about the change and a safe rewrite suggestion to preserve the 2021 semantics in most cases.

Related to #103108.
Related crater runs: https://github.com/rust-lang/rust/pull/129466.
This commit is contained in:
bors 2024-09-13 03:47:30 +00:00
commit a5efa01895
29 changed files with 1393 additions and 35 deletions
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compiler/rustc_middle/src/mir/mod.rs
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@ -1084,6 +1084,9 @@ pub enum LocalInfo<'tcx> {
/// (with no intervening statement context).
// FIXME(matthewjasper) Don't store in this in `Body`
BlockTailTemp(BlockTailInfo),
/// A temporary created during evaluating `if` predicate, possibly for pattern matching for `let`s,
/// and subject to Edition 2024 temporary lifetime rules
IfThenRescopeTemp { if_then: HirId },
/// A temporary created during the pass `Derefer` to avoid it's retagging
DerefTemp,
/// A temporary created for borrow checking.