[Clang][Sema] Partially revert changes to operator= from #90152

Author: sdkrystian

clang/lib/Sema/SemaExprMember.cpp

@@ -996,7 +996,10 @@ Sema::BuildMemberReferenceExpr(Expr *BaseExpr, QualType BaseExprType,
   // build a CXXDependentScopeMemberExpr.
   if (R.wasNotFoundInCurrentInstantiation() ||
       (IsArrow && !BaseExprType->isPointerType() &&
-       BaseExprType->isDependentType()))
+       BaseExprType->isDependentType()) ||
+      (R.getLookupName().getCXXOverloadedOperator() == OO_Equal &&
+       (SS.isSet() ? SS.getScopeRep()->isDependent()
+                   : BaseExprType->isDependentType())))
     return ActOnDependentMemberExpr(BaseExpr, BaseExprType, IsArrow, OpLoc, SS,
                                     TemplateKWLoc, FirstQualifierInScope,
                                     R.getLookupNameInfo(), TemplateArgs);

clang/lib/Sema/SemaLookup.cpp

@@ -1282,6 +1282,7 @@ bool Sema::CppLookupName(LookupResult &R, Scope *S) {
       if (DeclContext *DC = PreS->getEntity())
         DeclareImplicitMemberFunctionsWithName(*this, Name, R.getNameLoc(), DC);
   }
+
   // C++23 [temp.dep.general]p2:
   //   The component name of an unqualified-id is dependent if
   //   - it is a conversion-function-id whose conversion-type-id
@@ -1294,20 +1295,6 @@ bool Sema::CppLookupName(LookupResult &R, Scope *S) {
     return false;
   }
 
-  // If this is the name of an implicitly-declared special member function,
-  // go through the scope stack to implicitly declare
-  if (isImplicitlyDeclaredMemberFunctionName(Name)) {
-    for (Scope *PreS = S; PreS; PreS = PreS->getParent())
-      if (DeclContext *DC = PreS->getEntity()) {
-        if (DC->isDependentContext() && isa<CXXRecordDecl>(DC) &&
-            Name.getCXXOverloadedOperator() == OO_Equal) {
-          R.setNotFoundInCurrentInstantiation();
-          return false;
-        }
-        DeclareImplicitMemberFunctionsWithName(*this, Name, R.getNameLoc(), DC);
-      }
-  }
-
   // Implicitly declare member functions with the name we're looking for, if in
   // fact we are in a scope where it matters.
 
@@ -2485,10 +2472,8 @@ bool Sema::LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
     //     is operator=, or
     //   - [...]
     if (DeclarationName Name = R.getLookupName();
-        (Name.getNameKind() == DeclarationName::CXXConversionFunctionName &&
-         Name.getCXXNameType()->isDependentType()) ||
-        (Name.getCXXOverloadedOperator() == OO_Equal && LookupRec &&
-         LookupRec->isDependentContext())) {
+        Name.getNameKind() == DeclarationName::CXXConversionFunctionName &&
+        Name.getCXXNameType()->isDependentType()) {
       R.setNotFoundInCurrentInstantiation();
       return false;
     }

clang/lib/Sema/SemaTemplate.cpp

@@ -750,7 +750,8 @@ Sema::ActOnDependentIdExpression(const CXXScopeSpec &SS,
   if (!MightBeCxx11UnevalField && !isAddressOfOperand && !IsEnum &&
       isa<CXXMethodDecl>(DC) &&
       cast<CXXMethodDecl>(DC)->isImplicitObjectMemberFunction()) {
-    QualType ThisType = cast<CXXMethodDecl>(DC)->getThisType().getNonReferenceType();
+    QualType ThisType =
+        cast<CXXMethodDecl>(DC)->getThisType().getNonReferenceType();
 
     // Since the 'this' expression is synthesized, we don't need to
     // perform the double-lookup check.

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

@@ -453,6 +453,36 @@ namespace N3 {
       this->A::operator=(*this);
     }
   };
+
+  template<typename T>
+  struct C {
+    template<typename U>
+    void operator=(int);
+
+    void not_instantiated() {
+      operator=<int>(0);
+      C::operator=<int>(0);
+      this->operator=<int>(0);
+      this->C::operator=<int>(0);
+
+      operator=(*this);
+      C::operator=(*this);
+      this->operator=(*this);
+      this->C::operator=(*this);
+    }
+  };
+
+  template<typename T>
+  struct D {
+    auto not_instantiated() -> decltype(operator=(0)); // expected-error {{use of undeclared 'operator='}}
+  };
+
+  template<typename T>
+  struct E {
+    auto instantiated(E& e) -> decltype(operator=(e)); // expected-error {{use of undeclared 'operator='}}
+  };
+
+  template struct E<int>; // expected-note {{in instantiation of template class 'N3::E<int>' requested here}}
 } // namespace N3
 
 namespace N4 {
@@ -520,4 +550,5 @@ namespace N4 {
   };
 
   template void D<B>::instantiated(D); // expected-note {{in instantiation of}}
+
 } // namespace N4