Revert "[clang][Sema] Use original template pattern when declaring implicit deduction guides for nested template classes (#68379)"

This reverts commit dd0fba1.

It fails on nested classes that have both an explicit deduction guide and
a constructor that has an argument of the same type as the class (i.e. a copy constructor).

Author: antangelo

clang/docs/ReleaseNotes.rst

@@ -516,11 +516,6 @@ Bug Fixes to C++ Support
   rather than prefer the non-templated constructor as specified in
   [standard.group]p3.
 
-- Fix a bug where implicit deduction guides are not correctly generated for nested template
-  classes. Fixes:
-  (`#46200 <https://github.com/llvm/llvm-project/issues/46200>`_)
-  (`#57812 <https://github.com/llvm/llvm-project/issues/57812>`_)
-
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed an import failure of recursive friend class template.

clang/lib/Sema/SemaTemplate.cpp

@@ -2250,7 +2250,6 @@ struct ConvertConstructorToDeductionGuideTransform {
 
   Sema &SemaRef;
   ClassTemplateDecl *Template;
-  ClassTemplateDecl *NestedPattern = nullptr;
 
   DeclContext *DC = Template->getDeclContext();
   CXXRecordDecl *Primary = Template->getTemplatedDecl();
@@ -2328,8 +2327,6 @@ struct ConvertConstructorToDeductionGuideTransform {
     if (FTD) {
       Args.addOuterTemplateArguments(SubstArgs);
       Args.addOuterRetainedLevel();
-      if (NestedPattern)
-        Args.addOuterRetainedLevels(NestedPattern->getTemplateDepth());
     }
 
     FunctionProtoTypeLoc FPTL = CD->getTypeSourceInfo()->getTypeLoc()
@@ -2441,17 +2438,10 @@ struct ConvertConstructorToDeductionGuideTransform {
     SmallVector<QualType, 4> ParamTypes;
     const FunctionProtoType *T = TL.getTypePtr();
 
-    MultiLevelTemplateArgumentList OuterInstantiationArgs;
-    if (NestedPattern)
-      OuterInstantiationArgs = SemaRef.getTemplateInstantiationArgs(Template);
-
     //    -- The types of the function parameters are those of the constructor.
     for (auto *OldParam : TL.getParams()) {
       ParmVarDecl *NewParam =
           transformFunctionTypeParam(OldParam, Args, MaterializedTypedefs);
-      if (NestedPattern && NewParam)
-        NewParam = transformFunctionTypeParam(NewParam, OuterInstantiationArgs,
-                                              MaterializedTypedefs);
       if (!NewParam)
         return QualType();
       ParamTypes.push_back(NewParam->getType());
@@ -2657,23 +2647,13 @@ void Sema::DeclareImplicitDeductionGuides(TemplateDecl *Template,
   if (BuildingDeductionGuides.isInvalid())
     return;
 
-  // If the template is nested, then we need to use the original
-  // pattern to iterate over the constructors.
-  ClassTemplateDecl *Pattern = Transform.Template;
-  while (Pattern->getInstantiatedFromMemberTemplate()) {
-    if (Pattern->isMemberSpecialization())
-      break;
-    Pattern = Pattern->getInstantiatedFromMemberTemplate();
-    Transform.NestedPattern = Pattern;
-  }
-
   // Convert declared constructors into deduction guide templates.
   // FIXME: Skip constructors for which deduction must necessarily fail (those
   // for which some class template parameter without a default argument never
   // appears in a deduced context).
   llvm::SmallPtrSet<NamedDecl *, 8> ProcessedCtors;
   bool AddedAny = false;
-  for (NamedDecl *D : LookupConstructors(Pattern->getTemplatedDecl())) {
+  for (NamedDecl *D : LookupConstructors(Transform.Primary)) {
     D = D->getUnderlyingDecl();
     if (D->isInvalidDecl() || D->isImplicit())
       continue;