Reapply "[Clang][Sema] Use the correct lookup context when building overloaded 'operator->' in the current instantiation (llvm#104458)" (llvm#109422)

Reapplies llvm#104458, fixing a bug that occurs when a class member access expression calls an `operator->` operator function that returns a non-dependent class type.

Author: sdkrystian

clang/include/clang/Sema/Sema.h

@@ -10608,9 +10608,8 @@ class Sema final : public SemaBase {
   /// BuildOverloadedArrowExpr - Build a call to an overloaded @c operator->
   ///  (if one exists), where @c Base is an expression of class type and
   /// @c Member is the name of the member we're trying to find.
-  ExprResult BuildOverloadedArrowExpr(Scope *S, Expr *Base,
-                                      SourceLocation OpLoc,
-                                      bool *NoArrowOperatorFound = nullptr);
+  ExprResult BuildOverloadedArrowExpr(Expr *Base, SourceLocation OpLoc,
+                                      bool *NoArrowOperatorFound);
 
   ExprResult BuildCXXMemberCallExpr(Expr *Exp, NamedDecl *FoundDecl,
                                     CXXConversionDecl *Method,

clang/lib/Sema/SemaExprCXX.cpp

@@ -7999,18 +7999,6 @@ ExprResult Sema::ActOnStartCXXMemberReference(Scope *S, Expr *Base,
 
   QualType BaseType = Base->getType();
   MayBePseudoDestructor = false;
-  if (BaseType->isDependentType()) {
-    // If we have a pointer to a dependent type and are using the -> operator,
-    // the object type is the type that the pointer points to. We might still
-    // have enough information about that type to do something useful.
-    if (OpKind == tok::arrow)
-      if (const PointerType *Ptr = BaseType->getAs<PointerType>())
-        BaseType = Ptr->getPointeeType();
-
-    ObjectType = ParsedType::make(BaseType);
-    MayBePseudoDestructor = true;
-    return Base;
-  }
 
   // C++ [over.match.oper]p8:
   //   [...] When operator->returns, the operator-> is applied  to the value
@@ -8025,7 +8013,7 @@ ExprResult Sema::ActOnStartCXXMemberReference(Scope *S, Expr *Base,
     SmallVector<FunctionDecl*, 8> OperatorArrows;
     CTypes.insert(Context.getCanonicalType(BaseType));
 
-    while (BaseType->isRecordType()) {
+    while (BaseType->getAsRecordDecl()) {
       if (OperatorArrows.size() >= getLangOpts().ArrowDepth) {
         Diag(OpLoc, diag::err_operator_arrow_depth_exceeded)
           << StartingType << getLangOpts().ArrowDepth << Base->getSourceRange();
@@ -8036,7 +8024,7 @@ ExprResult Sema::ActOnStartCXXMemberReference(Scope *S, Expr *Base,
       }
 
       Result = BuildOverloadedArrowExpr(
-          S, Base, OpLoc,
+          Base, OpLoc,
           // When in a template specialization and on the first loop iteration,
           // potentially give the default diagnostic (with the fixit in a
           // separate note) instead of having the error reported back to here
@@ -8100,7 +8088,7 @@ ExprResult Sema::ActOnStartCXXMemberReference(Scope *S, Expr *Base,
   // it's legal for the type to be incomplete if this is a pseudo-destructor
   // call.  We'll do more incomplete-type checks later in the lookup process,
   // so just skip this check for ObjC types.
-  if (!BaseType->isRecordType()) {
+  if (BaseType->isDependentType() || !BaseType->isRecordType()) {
     ObjectType = ParsedType::make(BaseType);
     MayBePseudoDestructor = true;
     return Base;
@@ -8111,8 +8099,7 @@ ExprResult Sema::ActOnStartCXXMemberReference(Scope *S, Expr *Base,
   //   Unlike the object expression in other contexts, *this is not required to
   //   be of complete type for purposes of class member access (5.2.5) outside
   //   the member function body.
-  if (!BaseType->isDependentType() &&
-      !isThisOutsideMemberFunctionBody(BaseType) &&
+  if (!isThisOutsideMemberFunctionBody(BaseType) &&
       RequireCompleteType(OpLoc, BaseType,
                           diag::err_incomplete_member_access)) {
     return CreateRecoveryExpr(Base->getBeginLoc(), Base->getEndLoc(), {Base});

clang/lib/Sema/SemaExprMember.cpp

@@ -1357,7 +1357,7 @@ static ExprResult LookupMemberExpr(Sema &S, LookupResult &R,
       BaseType = Ptr->getPointeeType();
     else if (BaseType->isFunctionType())
       goto fail;
-    else if (BaseType->isDependentType())
+    else if (BaseExpr.get()->isTypeDependent())
       BaseType = S.Context.DependentTy;
     else if (BaseType->isRecordType()) {
       // Recover from arrow accesses to records, e.g.:

clang/lib/Sema/SemaOverload.cpp

@@ -15962,10 +15962,9 @@ Sema::BuildCallToObjectOfClassType(Scope *S, Expr *Obj,
   return CheckForImmediateInvocation(MaybeBindToTemporary(TheCall), Method);
 }
 
-ExprResult
-Sema::BuildOverloadedArrowExpr(Scope *S, Expr *Base, SourceLocation OpLoc,
-                               bool *NoArrowOperatorFound) {
-  assert(Base->getType()->isRecordType() &&
+ExprResult Sema::BuildOverloadedArrowExpr(Expr *Base, SourceLocation OpLoc,
+                                          bool *NoArrowOperatorFound) {
+  assert(Base->getType()->getAsRecordDecl() &&
          "left-hand side must have class type");
 
   if (checkPlaceholderForOverload(*this, Base))
@@ -15988,9 +15987,20 @@ Sema::BuildOverloadedArrowExpr(Scope *S, Expr *Base, SourceLocation OpLoc,
     return ExprError();
 
   LookupResult R(*this, OpName, OpLoc, LookupOrdinaryName);
-  LookupQualifiedName(R, Base->getType()->castAs<RecordType>()->getDecl());
+  LookupParsedName(R, /*S=*/nullptr, /*SS=*/nullptr, Base->getType());
   R.suppressAccessDiagnostics();
 
+  if (Base->getType()->isDependentType() &&
+      (!R.empty() || R.wasNotFoundInCurrentInstantiation())) {
+    DeclarationNameInfo OpNameInfo(OpName, OpLoc);
+    ExprResult Fn = CreateUnresolvedLookupExpr(
+        /*NamingClass=*/nullptr, /*NNSLoc=*/NestedNameSpecifierLoc(),
+        OpNameInfo, R.asUnresolvedSet(), /*PerformADL=*/false);
+    return CXXOperatorCallExpr::Create(Context, OO_Arrow, Fn.get(), Base,
+                                       Context.DependentTy, VK_PRValue, OpLoc,
+                                       CurFPFeatureOverrides());
+  }
+
   for (LookupResult::iterator Oper = R.begin(), OperEnd = R.end();
        Oper != OperEnd; ++Oper) {
     AddMethodCandidate(Oper.getPair(), Base->getType(), Base->Classify(Context),

clang/lib/Sema/TreeTransform.h

@@ -17282,10 +17282,11 @@ ExprResult TreeTransform<Derived>::RebuildCXXOperatorCallExpr(
   } else if (Op == OO_Arrow) {
     // It is possible that the type refers to a RecoveryExpr created earlier
     // in the tree transformation.
-    if (First->getType()->isDependentType())
+    if (First->containsErrors())
       return ExprError();
     // -> is never a builtin operation.
-    return SemaRef.BuildOverloadedArrowExpr(nullptr, First, OpLoc);
+    return getSema().BuildOverloadedArrowExpr(First, OpLoc,
+                                              /*NoArrowOperatorFound=*/nullptr);
   } else if (Second == nullptr || isPostIncDec) {
     if (!First->getType()->isOverloadableType() ||
         (Op == OO_Amp && getSema().isQualifiedMemberAccess(First))) {

clang/test/CXX/temp/temp.res/temp.dep/temp.dep.type/p4.cpp

@@ -484,16 +484,19 @@ namespace N4 {
   template<typename T>
   struct A {
     void not_instantiated(A a, A<T> b, T c) {
-      a->x;
-      b->x;
+      a->x; // expected-error {{member reference type 'A<T>' is not a pointer; did you mean to use '.'?}}
+      b->x; // expected-error {{member reference type 'A<T>' is not a pointer; did you mean to use '.'?}}
       c->x;
     }
 
     void instantiated(A a, A<T> b, T c) {
-      a->x; // expected-error {{member reference type 'A<int>' is not a pointer; did you mean to use '.'?}}
-            // expected-error@-1 {{no member named 'x' in 'N4::A<int>'}}
-      b->x; // expected-error {{member reference type 'A<int>' is not a pointer; did you mean to use '.'?}}
-            // expected-error@-1 {{no member named 'x' in 'N4::A<int>'}}
+      // FIXME: We should only emit a single diagnostic suggesting to use '.'!
+      a->x; // expected-error {{member reference type 'A<T>' is not a pointer; did you mean to use '.'?}}
+            // expected-error@-1 {{member reference type 'A<int>' is not a pointer; did you mean to use '.'?}}
+            // expected-error@-2 {{no member named 'x' in 'N4::A<int>'}}
+      b->x; // expected-error {{member reference type 'A<T>' is not a pointer; did you mean to use '.'?}}
+            // expected-error@-1 {{member reference type 'A<int>' is not a pointer; did you mean to use '.'?}}
+            // expected-error@-2 {{no member named 'x' in 'N4::A<int>'}}
       c->x; // expected-error {{member reference type 'int' is not a pointer}}
     }
   };
@@ -540,11 +543,10 @@ namespace N4 {
       a->T::f();
       a->T::g();
 
-      // FIXME: 'U' should be a dependent name, and its lookup context should be 'a.operator->()'!
-      a->U::x; // expected-error {{use of undeclared identifier 'U'}}
-      a->U::y; // expected-error {{use of undeclared identifier 'U'}}
-      a->U::f(); // expected-error {{use of undeclared identifier 'U'}}
-      a->U::g(); // expected-error {{use of undeclared identifier 'U'}}
+      a->U::x;
+      a->U::y;
+      a->U::f();
+      a->U::g();
     }
 
     void instantiated(D a) {
@@ -605,3 +607,24 @@ namespace N5 {
 
   template void g(int); // expected-note {{in instantiation of}}
 } // namespace N5
+
+namespace N6 {
+  struct A {
+    int x;
+  };
+
+  struct B {
+    A* operator->();
+  };
+
+  struct C {
+    B y;
+  };
+
+  template<typename T>
+  struct D : C {
+    void f() {
+      y->x;
+    }
+  };
+} // namespace N6