[CodeComplete] Don't drop ArrayToPointerDecay when doing member completion (llvm#134951)

Fixes llvm#123146.

rdar://138851576

Author: ahatanak

clang/lib/Sema/SemaCodeComplete.cpp

@@ -5726,7 +5726,10 @@ class ConceptInfo {
 QualType getApproximateType(const Expr *E, HeuristicResolver &Resolver) {
   if (E->getType().isNull())
     return QualType();
-  E = E->IgnoreParenImpCasts();
+  // Don't drop implicit cast if it's an array decay.
+  if (auto *ICE = dyn_cast<ImplicitCastExpr>(E);
+      !ICE || ICE->getCastKind() != CK_ArrayToPointerDecay)
+    E = E->IgnoreParenImpCasts();
   QualType Unresolved = E->getType();
   // Resolve DependentNameType
   if (const auto *DNT = Unresolved->getAs<DependentNameType>()) {

clang/test/CodeCompletion/member-access.c

@@ -36,3 +36,12 @@ void test4(struct Point *p) {
 }
 // RUN: %clang_cc1 -fsyntax-only -code-completion-with-fixits -code-completion-at=%s:%(line-3):13 %s -o - | FileCheck -check-prefix=CHECK-CC1 %s
 // RUN: %clang_cc1 -fsyntax-only -code-completion-with-fixits -code-completion-at=%s:%(line-3):23 %s -o - | FileCheck -check-prefix=CHECK-CC1 %s
+
+float test5(void) {
+  struct Point array[4];
+  return array->x;
+}
+// RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:%(line-2):17 %s -o - | FileCheck -check-prefix=CHECK-CC4 %s
+// CHECK-CC4: COMPLETION: x : [#float#]x
+// CHECK-CC4: COMPLETION: y : [#float#]y
+// CHECK-CC4: COMPLETION: z : [#float#]z