[clang][CodeComplete] Recurse into the subexpression of deref operator in getApproximateType (llvm#93404)

The issue with the previous implementation bc31be7 was that
getApproximateType could potentially return a null QualType for a
dereferencing operator, which is not what its caller wants.

Author: zyn0217

clang/lib/Sema/SemaCodeComplete.cpp

@@ -5692,8 +5692,15 @@ QualType getApproximateType(const Expr *E) {
     }
   }
   if (const auto *UO = llvm::dyn_cast<UnaryOperator>(E)) {
-    if (UO->getOpcode() == UnaryOperatorKind::UO_Deref)
-      return UO->getSubExpr()->getType()->getPointeeType();
+    if (UO->getOpcode() == UnaryOperatorKind::UO_Deref) {
+      // We recurse into the subexpression because it could be of dependent
+      // type.
+      if (auto Pointee = getApproximateType(UO->getSubExpr())->getPointeeType();
+          !Pointee.isNull())
+        return Pointee;
+      // Our caller expects a non-null result, even though the SubType is
+      // supposed to have a pointee. Fall through to Unresolved anyway.
+    }
   }
   return Unresolved;
 }

clang/test/CodeCompletion/member-access.cpp

@@ -367,4 +367,20 @@ class A {
 // CHECK-DEREF-THIS: [#void#]function()
   }
 };
+
+template <typename Element>
+struct RepeatedField {
+  void Add();
+};
+
+template <typename T>
+RepeatedField<T>* MutableRepeatedField() {}
+
+template <class T>
+void Foo() {
+  auto& C = *MutableRepeatedField<T>();
+  C.
+}
+// RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:382:5 %s -o - | FileCheck -check-prefix=CHECK-DEREF-DEPENDENT %s
+// CHECK-DEREF-DEPENDENT: [#void#]Add()
 }