[clang] Track final substitution for SubstTemplateTemplateParm nodes

Author: mizvekov

clang/include/clang/AST/ASTContext.h

@@ -2396,10 +2396,11 @@ class ASTContext : public RefCountedBase<ASTContext> {
                                         const IdentifierInfo *Name) const;
   TemplateName getDependentTemplateName(NestedNameSpecifier *NNS,
                                         OverloadedOperatorKind Operator) const;
-  TemplateName
-  getSubstTemplateTemplateParm(TemplateName replacement, Decl *AssociatedDecl,
-                               unsigned Index,
-                               std::optional<unsigned> PackIndex) const;
+  TemplateName getSubstTemplateTemplateParm(TemplateName replacement,
+                                            Decl *AssociatedDecl,
+                                            unsigned Index,
+                                            std::optional<unsigned> PackIndex,
+                                            bool Final) const;
   TemplateName getSubstTemplateTemplateParmPack(const TemplateArgument &ArgPack,
                                                 Decl *AssociatedDecl,
                                                 unsigned Index,

clang/include/clang/AST/PropertiesBase.td

@@ -729,8 +729,9 @@ let Class = PropertyTypeCase<TemplateName, "SubstTemplateTemplateParm"> in {
   def : Property<"packIndex", Optional<UInt32>> {
     let Read = [{ parm->getPackIndex() }];
   }
+  def : Property<"final", Bool> { let Read = [{ parm->getFinal() }]; }
   def : Creator<[{
-    return ctx.getSubstTemplateTemplateParm(replacement, associatedDecl, index, packIndex);
+    return ctx.getSubstTemplateTemplateParm(replacement, associatedDecl, index, packIndex, final);
   }]>;
 }
 let Class = PropertyTypeCase<TemplateName, "SubstTemplateTemplateParmPack"> in {

clang/include/clang/AST/TemplateName.h

@@ -413,9 +413,11 @@ class SubstTemplateTemplateParmStorage
 
   SubstTemplateTemplateParmStorage(TemplateName Replacement,
                                    Decl *AssociatedDecl, unsigned Index,
-                                   std::optional<unsigned> PackIndex)
+                                   std::optional<unsigned> PackIndex,
+                                   bool Final)
       : UncommonTemplateNameStorage(SubstTemplateTemplateParm, Index,
-                                    PackIndex ? *PackIndex + 1 : 0),
+                                    ((PackIndex ? *PackIndex + 1 : 0) << 1) |
+                                        Final),
         Replacement(Replacement), AssociatedDecl(AssociatedDecl) {
     assert(AssociatedDecl != nullptr);
   }
@@ -429,10 +431,15 @@ class SubstTemplateTemplateParmStorage
   /// This should match the result of `getParameter()->getIndex()`.
   unsigned getIndex() const { return Bits.Index; }
 
+  // This substitution is Final, which means the substitution is fully
+  // sugared: it doesn't need to be resugared later.
+  bool getFinal() const { return Bits.Data & 1; }
+
   std::optional<unsigned> getPackIndex() const {
-    if (Bits.Data == 0)
+    auto Data = Bits.Data >> 1;
+    if (Data == 0)
       return std::nullopt;
-    return Bits.Data - 1;
+    return Data - 1;
   }
 
   TemplateTemplateParmDecl *getParameter() const;
@@ -442,7 +449,7 @@ class SubstTemplateTemplateParmStorage
 
   static void Profile(llvm::FoldingSetNodeID &ID, TemplateName Replacement,
                       Decl *AssociatedDecl, unsigned Index,
-                      std::optional<unsigned> PackIndex);
+                      std::optional<unsigned> PackIndex, bool Final);
 };
 
 class DeducedTemplateStorage : public UncommonTemplateNameStorage,

clang/include/clang/AST/Type.h

@@ -6475,7 +6475,8 @@ class SubstTemplateTypeParmPackType : public Type, public llvm::FoldingSetNode {
   /// This should match the result of `getReplacedParameter()->getIndex()`.
   unsigned getIndex() const { return SubstTemplateTypeParmPackTypeBits.Index; }
 
-  // When true the substitution will be 'Final' (subst node won't be placed).
+  // This substitution will be Final, which means the substitution will be fully
+  // sugared: it doesn't need to be resugared later.
   bool getFinal() const;
 
   unsigned getNumArgs() const {

clang/lib/AST/ASTContext.cpp

@@ -10133,18 +10133,18 @@ ASTContext::getDependentTemplateName(NestedNameSpecifier *NNS,
 
 TemplateName ASTContext::getSubstTemplateTemplateParm(
     TemplateName Replacement, Decl *AssociatedDecl, unsigned Index,
-    std::optional<unsigned> PackIndex) const {
+    std::optional<unsigned> PackIndex, bool Final) const {
   llvm::FoldingSetNodeID ID;
   SubstTemplateTemplateParmStorage::Profile(ID, Replacement, AssociatedDecl,
-                                            Index, PackIndex);
+                                            Index, PackIndex, Final);
 
   void *insertPos = nullptr;
   SubstTemplateTemplateParmStorage *subst
     = SubstTemplateTemplateParms.FindNodeOrInsertPos(ID, insertPos);
 
   if (!subst) {
     subst = new (*this) SubstTemplateTemplateParmStorage(
-        Replacement, AssociatedDecl, Index, PackIndex);
+        Replacement, AssociatedDecl, Index, PackIndex, Final);
     SubstTemplateTemplateParms.InsertNode(subst, insertPos);
   }
 

clang/lib/AST/ASTImporter.cpp

@@ -9959,7 +9959,7 @@ Expected<TemplateName> ASTImporter::Import(TemplateName From) {
 
     return ToContext.getSubstTemplateTemplateParm(
         *ReplacementOrErr, *AssociatedDeclOrErr, Subst->getIndex(),
-        Subst->getPackIndex());
+        Subst->getPackIndex(), Subst->getFinal());
   }
 
   case TemplateName::SubstTemplateTemplateParmPack: {

clang/lib/AST/TemplateName.cpp

@@ -77,16 +77,18 @@ SubstTemplateTemplateParmStorage::getParameter() const {
 }
 
 void SubstTemplateTemplateParmStorage::Profile(llvm::FoldingSetNodeID &ID) {
-  Profile(ID, Replacement, getAssociatedDecl(), getIndex(), getPackIndex());
+  Profile(ID, Replacement, getAssociatedDecl(), getIndex(), getPackIndex(),
+          getFinal());
 }
 
 void SubstTemplateTemplateParmStorage::Profile(
     llvm::FoldingSetNodeID &ID, TemplateName Replacement, Decl *AssociatedDecl,
-    unsigned Index, std::optional<unsigned> PackIndex) {
+    unsigned Index, std::optional<unsigned> PackIndex, bool Final) {
   Replacement.Profile(ID);
   ID.AddPointer(AssociatedDecl);
   ID.AddInteger(Index);
   ID.AddInteger(PackIndex ? *PackIndex + 1 : 0);
+  ID.AddBoolean(Final);
 }
 
 SubstTemplateTemplateParmPackStorage::SubstTemplateTemplateParmPackStorage(

clang/lib/AST/TextNodeDumper.cpp

@@ -1302,6 +1302,8 @@ void TextNodeDumper::dumpBareTemplateName(TemplateName TN) {
     OS << " index " << STS->getIndex();
     if (std::optional<unsigned int> PackIndex = STS->getPackIndex())
       OS << " pack_index " << *PackIndex;
+    if (STS->getFinal())
+      OS << " final";
     if (const TemplateTemplateParmDecl *P = STS->getParameter())
       AddChild("parameter", [=] { Visit(P); });
     dumpDeclRef(STS->getAssociatedDecl(), "associated");

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -2083,10 +2083,8 @@ TemplateName TemplateInstantiator::TransformTemplateName(
       TemplateName Template = Arg.getAsTemplate();
       assert(!Template.isNull() && "Null template template argument");
 
-      if (Final)
-        return Template;
       return getSema().Context.getSubstTemplateTemplateParm(
-          Template, AssociatedDecl, TTP->getIndex(), PackIndex);
+          Template, AssociatedDecl, TTP->getIndex(), PackIndex, Final);
     }
   }
 
@@ -2098,11 +2096,9 @@ TemplateName TemplateInstantiator::TransformTemplateName(
     TemplateArgument Pack = SubstPack->getArgumentPack();
     TemplateName Template =
         getPackSubstitutedTemplateArgument(getSema(), Pack).getAsTemplate();
-    if (SubstPack->getFinal())
-      return Template;
     return getSema().Context.getSubstTemplateTemplateParm(
         Template, SubstPack->getAssociatedDecl(), SubstPack->getIndex(),
-        getPackIndex(Pack));
+        getPackIndex(Pack), SubstPack->getFinal());
   }
 
   return inherited::TransformTemplateName(SS, Name, NameLoc, ObjectType,