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Rollup merge of #103031 - est31:match_guard_irrefutable_let, r=oli-obk

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Suppress irrefutable let patterns lint for prefixes in match guards

In match guards, irrefutable prefixes might use the bindings created by the match pattern. Ideally, we check for this, but we can do the next best thing and just not lint for irrefutable prefixes in match guards.

Fixes #98361
This commit is contained in:
Dylan DPC 2022-10-14 16:19:16 +05:30 • committed by GitHub
commit 7cf09c57a2
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3 changed files with 36 additions and 19 deletions
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18
compiler/rustc_mir_build/src/thir/pattern/check_match.rs
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@ -370,8 +370,12 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
// Check if the let source is while, for there is no alternative place to put a prefix,
// and we shouldn't lint.
// For let guards inside a match, prefixes might use bindings of the match pattern,
// so can't always be moved out.
// FIXME: Add checking whether the bindings are actually used in the prefix,
// and lint if they are not.
let let_source = let_source_parent(self.tcx, top, None);
if !matches!(let_source, LetSource::WhileLet) {
if !matches!(let_source, LetSource::WhileLet | LetSource::IfLetGuard) {
// Emit the lint
let prefix = &chain_refutabilities[..until];
lint_affix(prefix, "leading", "outside of the construct");
@ -1151,10 +1155,14 @@ fn let_source_parent(tcx: TyCtxt<'_>, parent: HirId, pat_id: Option<HirId>) -> L
let parent_parent = hir.get_parent_node(parent);
let parent_parent_node = hir.get(parent_parent);
if let hir::Node::Stmt(hir::Stmt { kind: hir::StmtKind::Local(_), span, .. }) =
parent_parent_node
{
return LetSource::LetElse(*span);
match parent_parent_node {
hir::Node::Stmt(hir::Stmt { kind: hir::StmtKind::Local(_), span, .. }) => {
return LetSource::LetElse(*span);
}
hir::Node::Arm(hir::Arm { guard: Some(hir::Guard::If(_)), .. }) => {
return LetSource::IfLetGuard;
}
_ => {}
}
let parent_parent_parent = hir.get_parent_node(parent_parent);