Rollup merge of #141267 - dianne:fix-141265, r=oli-obk

only resolve top-level guard patterns' guards once

We resolve guard patterns' guards in `resolve_pattern_inner`, so to avoid resolving them multiple times, we must avoid doing so earlier. To accomplish this, `LateResolutionVisitor::visit_pat` contains a case for guard patterns that avoids visiting their guards while walking patterns.

This PR fixes #141265, which was due to `visit::walk_pat` being used instead; this meant guards at the top level of a pattern would be visited twice. e.g. it would ICE on `for x if x in [] {}`, but not `for (x if x) in [] {}`. `visit_pat` was already used for the guard pattern in the second example, on account of the top-level pattern being parens.

1 files changed, 3 insertions, 1 deletions

diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index 1b682d0cf8a..fd977a8eb6c 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -3901,7 +3901,9 @@ impl<'a, 'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
         // We walk the pattern before declaring the pattern's inner bindings,
         // so that we avoid resolving a literal expression to a binding defined
         // by the pattern.
-        visit::walk_pat(self, pat);
+        // NB: `Self::visit_pat` must be used rather than `visit::walk_pat` to avoid resolving guard
+        // patterns' guard expressions multiple times (#141265).
+        self.visit_pat(pat);
         self.resolve_pattern_inner(pat, pat_src, bindings);
         // This has to happen *after* we determine which pat_idents are variants:
         self.check_consistent_bindings(pat);