Revert "[Clang][Sema] Fix template name lookup for operator= (llvm#90999)"

This reverts commit 3191e0b.

Author: sdkrystian

clang/lib/Sema/SemaLookup.cpp

@@ -1300,8 +1300,7 @@ bool Sema::CppLookupName(LookupResult &R, Scope *S) {
     for (Scope *PreS = S; PreS; PreS = PreS->getParent())
       if (DeclContext *DC = PreS->getEntity()) {
         if (DC->isDependentContext() && isa<CXXRecordDecl>(DC) &&
-            Name.getCXXOverloadedOperator() == OO_Equal &&
-            !R.isTemplateNameLookup()) {
+            Name.getCXXOverloadedOperator() == OO_Equal) {
           R.setNotFoundInCurrentInstantiation();
           return false;
         }
@@ -2472,8 +2471,10 @@ bool Sema::LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
     }
   } QL(LookupCtx);
 
-  bool TemplateNameLookup = R.isTemplateNameLookup();
   CXXRecordDecl *LookupRec = dyn_cast<CXXRecordDecl>(LookupCtx);
+  // FIXME: Per [temp.dep.general]p2, an unqualified name is also dependent
+  // if it's a dependent conversion-function-id or operator= where the current
+  // class is a templated entity. This should be handled in LookupName.
   if (!InUnqualifiedLookup && !R.isForRedeclaration()) {
     // C++23 [temp.dep.type]p5:
     //   A qualified name is dependent if
@@ -2487,7 +2488,7 @@ bool Sema::LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
         (Name.getNameKind() == DeclarationName::CXXConversionFunctionName &&
          Name.getCXXNameType()->isDependentType()) ||
         (Name.getCXXOverloadedOperator() == OO_Equal && LookupRec &&
-         LookupRec->isDependentContext() && !TemplateNameLookup)) {
+         LookupRec->isDependentContext())) {
       R.setNotFoundInCurrentInstantiation();
       return false;
     }
@@ -2583,6 +2584,8 @@ bool Sema::LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
     return true;
   };
 
+  bool TemplateNameLookup = R.isTemplateNameLookup();
+
   // Determine whether two sets of members contain the same members, as
   // required by C++ [class.member.lookup]p6.
   auto HasSameDeclarations = [&](DeclContext::lookup_iterator A,

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

@@ -453,24 +453,6 @@ 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);
-    }
-  };
 } // namespace N3
 
 namespace N4 {