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Rollup merge of #133753 - dingxiangfei2009:reduce-false-positive-if-let-rescope, r=jieyouxu

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Reduce false positives on some common cases from if-let-rescope lint

r? `@jieyouxu`

We would like to identify a very common case in the ecosystem in which we do not need to apply the lint suggestion for the new Edition 2024 `if let` semantics.

In this patch we excluded linting from `if let`s in statements and block tail expressions. In these simple cases, new Edition 2024 drop orders are identical to those of Edition 2021 and prior.

However, conservatively we should still lint for the other cases, because [this example](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=2113df5ce78f161d32a1190faf5c7469) shows that the drop order changes are very pronounced, some of which are even sensitive to runtime data.
This commit is contained in:
Matthias Krüger 2024-12-03 17:27:08 +01:00 • committed by GitHub
commit 93781324db
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4 changed files with 47 additions and 40 deletions
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7
compiler/rustc_lint/src/if_let_rescope.rs
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@ -103,8 +103,11 @@ fn expr_parent_is_else(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> bool {
}
fn expr_parent_is_stmt(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> bool {
let Some((_, hir::Node::Stmt(stmt))) = tcx.hir().parent_iter(hir_id).next() else {
return false;
let mut parents = tcx.hir().parent_iter(hir_id);
let stmt = match parents.next() {
Some((_, hir::Node::Stmt(stmt))) => stmt,
Some((_, hir::Node::Block(_) | hir::Node::Arm(_))) => return true,
_ => return false,
};
let (hir::StmtKind::Semi(expr) | hir::StmtKind::Expr(expr)) = stmt.kind else { return false };
expr.hir_id == hir_id