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Rollup merge of #103034 - nathanwhit:let-chains-rhs-temporaries, r=wesleywiser

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Let expressions on RHS shouldn't be terminating scopes

Fixes #100276.

Before this PR, we were unconditionally marking the RHS of short-circuiting binary expressions as a terminating scope.

In the case of a let chain where the `let` expression was on the RHS, this meant that temporaries within the `let` expr would only live until the end of the expression. Since this only affected the RHS, this led to surprising behavior ([example](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=d1b0a5d1f01882f9c89c2194a75eb19f)).

After this PR, we only mark the RHS as a terminating scope if it is not a `let` expression.
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Dylan DPC 2022-10-19 14:05:52 +05:30 • committed by GitHub
commit 48c5e0c262
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4 changed files with 24 additions and 8 deletions
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8
compiler/rustc_hir_analysis/src/check/region.rs
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@ -252,9 +252,13 @@ fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx h
) => {
// For shortcircuiting operators, mark the RHS as a terminating
// scope since it only executes conditionally.
terminating(r.hir_id.local_id);
}
// `Let` expressions (in a let-chain) shouldn't be terminating, as their temporaries
// should live beyond the immediate expression
if !matches!(r.kind, hir::ExprKind::Let(_)) {
terminating(r.hir_id.local_id);
}
}
hir::ExprKind::If(_, ref then, Some(ref otherwise)) => {
terminating(then.hir_id.local_id);
terminating(otherwise.hir_id.local_id);