[clang] NFCI: remove obsolete workaround for template default arguments

This removes a workaround for template template arguments pointing to
older template declarations, which don't have the most recent default
argument definition.

The removed workaround was introduced in 1abacfc,
but #75569 introduced a
better fix which is more comprehensive and doesn't require rebuilding
TemplateNames.

Author: mizvekov

clang/include/clang/AST/TemplateName.h

@@ -314,11 +314,6 @@ class TemplateName {
 
   TemplateName getUnderlying() const;
 
-  /// Get the template name to substitute when this template name is used as a
-  /// template template argument. This refers to the most recent declaration of
-  /// the template, including any default template arguments.
-  TemplateName getNameToSubstitute() const;
-
   TemplateNameDependence getDependence() const;
 
   /// Determines whether this is a dependent template name.

clang/lib/AST/TemplateName.cpp

@@ -214,23 +214,6 @@ UsingShadowDecl *TemplateName::getAsUsingShadowDecl() const {
   return nullptr;
 }
 
-TemplateName TemplateName::getNameToSubstitute() const {
-  TemplateDecl *Decl = getAsTemplateDecl();
-
-  // Substituting a dependent template name: preserve it as written.
-  if (!Decl)
-    return *this;
-
-  // If we have a template declaration, use the most recent non-friend
-  // declaration of that template.
-  Decl = cast<TemplateDecl>(Decl->getMostRecentDecl());
-  while (Decl->getFriendObjectKind()) {
-    Decl = cast<TemplateDecl>(Decl->getPreviousDecl());
-    assert(Decl && "all declarations of template are friends");
-  }
-  return TemplateName(Decl);
-}
-
 TemplateNameDependence TemplateName::getDependence() const {
   auto D = TemplateNameDependence::None;
   switch (getKind()) {

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -1856,7 +1856,7 @@ Decl *TemplateInstantiator::TransformDecl(SourceLocation Loc, Decl *D) {
         Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
       }
 
-      TemplateName Template = Arg.getAsTemplate().getNameToSubstitute();
+      TemplateName Template = Arg.getAsTemplate();
       assert(!Template.isNull() && Template.getAsTemplateDecl() &&
              "Wrong kind of template template argument");
       return Template.getAsTemplateDecl();
@@ -2029,10 +2029,8 @@ TemplateName TemplateInstantiator::TransformTemplateName(
         Arg = getPackSubstitutedTemplateArgument(getSema(), Arg);
       }
 
-      TemplateName Template = Arg.getAsTemplate().getNameToSubstitute();
+      TemplateName Template = Arg.getAsTemplate();
       assert(!Template.isNull() && "Null template template argument");
-      assert(!Template.getAsQualifiedTemplateName() &&
-             "template decl to substitute is qualified?");
 
       if (Final)
         return Template;
@@ -2052,8 +2050,8 @@ TemplateName TemplateInstantiator::TransformTemplateName(
     if (SubstPack->getFinal())
       return Template;
     return getSema().Context.getSubstTemplateTemplateParm(
-        Template.getNameToSubstitute(), SubstPack->getAssociatedDecl(),
-        SubstPack->getIndex(), getPackIndex(Pack));
+        Template, SubstPack->getAssociatedDecl(), SubstPack->getIndex(),
+        getPackIndex(Pack));
   }
 
   return inherited::TransformTemplateName(SS, Name, NameLoc, ObjectType,