[CS] Set the naming pattern in markInvalid

This normally gets populated by successful type-checking, we still want
to populate it if we fail though to avoid attempting to type-check the
parent statement again.

Author: hamishknight

lib/Sema/SyntacticElementTarget.cpp

@@ -307,6 +307,12 @@ void SyntacticElementTarget::markInvalid() const {
 
     PreWalkResult<Pattern *> walkToPatternPre(Pattern *P) override {
       P->setType(ErrorType::get(Ctx));
+
+      // For a named pattern, set it on the variable. This stops us from
+      // attempting to double-type-check variables we've already type-checked.
+      if (auto *NP = dyn_cast<NamedPattern>(P))
+        NP->getDecl()->setNamingPattern(NP);
+
       return Action::Continue(P);
     }
 

test/Constraints/issue-66553.swift

@@ -4,7 +4,7 @@
 
 func baz(y: [Int], z: Int) -> Int {
   switch z {
-  case y[let z]: // expected-error 2{{'let' binding pattern cannot appear in an expression}}
+  case y[let z]: // expected-error {{'let' binding pattern cannot appear in an expression}}
     z
   default:
     z

test/Parse/matching_patterns.swift

@@ -406,7 +406,7 @@ func testNonBinding5(_ x: Int, y: [Int]) {
 func testNonBinding6(y: [Int], z: Int) -> Int {
   switch 0 {
   // We treat 'z' here as a binding, which is invalid.
-  case let y[z]: // expected-error 2{{pattern variable binding cannot appear in an expression}}
+  case let y[z]: // expected-error {{pattern variable binding cannot appear in an expression}}
     z
   case y[z]: // This is fine
     0