[ASTImporter] Support new kinds of declarations (mostly Using*)

[a.sidorin]

Summary

Support new AST nodes:

• UnresolvedUsingType
• EmptyDecl
• NamespaceAliasDecl
• UsingDecl
• UsingShadowDecl
• UsingDirectiveDecl
• UnresolvedUsingValueDecl
• UnresolvedUsingTypenameDecl

Refactor error handling in ImportTemplateArgumentLoc() method.
Add a test for inline namespaces.

Please take a look at FIXMEs I left in some places where I'm not sure that I have chosen a correct solution.
Also, I have some doubts for duplicating NamespaceAliasDecls. I found presence of such decls harmless but maybe I'm not correct here. I left NOTE comments both in the patch and in the tests for it.

[xazax.hun]

Looks good for me, I only have a few questions. Could you reupload the diff with contexts? It might make the review easier for others.

lib/AST/ASTImporter.cpp

1311

Don't we need an Importer.Imported call here?

1461

Minor nit: do we need the any in this sentence?

[a.sidorin]

Address review comments; add the context.

[xazax.hun]

LGTM! Adding Peter as a reviewer, as he is more experienced with the ASTImporter than me.

[szepet]

lib/AST/ASTImporter.cpp

1464

Since the Import can result nullptr (which is checked 2 lines below) this should be a cast_or_null as I see.

[a.sidorin]

Replaced cast<> with cast_or_null<>.

[a.sidorin]

Removed accidentally duplicated comment.

lib/AST/ASTImporter.cpp

1311

It's done a level upper in ASTImporter::ImportDecl() but I think it's worth it to add an explicit call.

1464

Nice spot, thank you!

[szepet]

Some nits added, other than these it looks good to me. Thank you!
Just more one question, I can see 3 different cases how the import returns are handled:

• if(!ToDecl) return nullptr;
• if(!ToDecl && FromDecl) return nullptr;
• no handling: ObjectXY::Create(...Import(FromDecl))

My question is the following: which cases require a check and which decls can be imported without checking the return value of the import function?
(Yepp, it could be asked in more general about the Importer, since things like this would be great to follow a convention. I have found some cases where it was not obivous to me which way to check. )

lib/AST/ASTImporter.cpp

2993

nit: As I see these cases typically handled in the way:

FrPattern = .;
ToPattern = ..;
if(FrPattern && !ToPattern)

Just to avoid the nested ifstmt.

3000

I dont see the problem with moving these up , collect nad investigate them in a smallset before the Create function, then adding them to the created ToUsing decl. It could be done as a follow up patch, dont want to mark it as a blocking issue.

3042

the same nit as above

3043

Does not this causes the same FIXME problem as above?

[a.sidorin]

Hello Peter,
if (!ToDecl) return nullptr; is used if original node is always non-null.
if(!ToDecl && FromDecl) return nullptr; is used if original node can be null. If the imported node is null, the result of import is null as well so such import is OK.
ObjectXY::Create(...Import(FromDecl)) is often used for source locations - as I guess, invalid source location is OK usually. It can also be used if we know that node should already be imported, but usually indicates a potential error.

[a.sidorin]

Add a FIXME.

[a.sidorin]

lib/AST/ASTImporter.cpp

2993

The logic is a bit more complicated. There are 3 cases:

1. Both FromPattern and ToPattern are nullptrs. Just continue.
2. FromPattern is non-null and ToPattern is null. Return error (nullptr).
3. Both FromPattern and ToPattern are nullptrs. Do the set... action.

So, it will require nested ifs or a code like:

if (FromPattern && ToPattern)
  set...
if (FromPattern && !ToPattern)
  return nullptr;

3000

There is a chicken and egg problem: both UsingShadowDecl and UsingDecl reference each other and UsingShadowDecl gets referenced UsingDecl as a ctor argument. If you have a good idea on how to resolve this dependency correctly, please point me.

[a.sidorin]

Closed with rL318776 (forgot Differential Revision, sorry).

lib/AST/ASTImporter.cpp

public:
     QualType VisitIncompleteArrayType(const IncompleteArrayType *T);
     QualType VisitVariableArrayType(const VariableArrayType *T);
     // FIXME: DependentSizedArrayType
     // FIXME: DependentSizedExtVectorType
     QualType VisitVectorType(const VectorType *T);
     QualType VisitExtVectorType(const ExtVectorType *T);
     QualType VisitFunctionNoProtoType(const FunctionNoProtoType *T);
     QualType VisitFunctionProtoType(const FunctionProtoType *T);
-    // FIXME: UnresolvedUsingType
+    QualType VisitUnresolvedUsingType(const UnresolvedUsingType *T);
     QualType VisitParenType(const ParenType *T);
     QualType VisitTypedefType(const TypedefType *T);
     QualType VisitTypeOfExprType(const TypeOfExprType *T);
     // FIXME: DependentTypeOfExprType
     QualType VisitTypeOfType(const TypeOfType *T);
     QualType VisitDecltypeType(const DecltypeType *T);
     QualType VisitUnaryTransformType(const UnaryTransformType *T);
     QualType VisitAutoType(const AutoType *T);
bool ImportDefinition(EnumDecl *From, EnumDecl *To,
                           ImportDefinitionKind Kind = IDK_Default);
     bool ImportDefinition(ObjCInterfaceDecl *From, ObjCInterfaceDecl *To,
                           ImportDefinitionKind Kind = IDK_Default);
     bool ImportDefinition(ObjCProtocolDecl *From, ObjCProtocolDecl *To,
                           ImportDefinitionKind Kind = IDK_Default);
     TemplateParameterList *ImportTemplateParameterList(
                                                  TemplateParameterList *Params);
     TemplateArgument ImportTemplateArgument(const TemplateArgument &From);
-    TemplateArgumentLoc ImportTemplateArgumentLoc(
-        const TemplateArgumentLoc &TALoc, bool &Error);
+    Optional<TemplateArgumentLoc> ImportTemplateArgumentLoc(
+        const TemplateArgumentLoc &TALoc);
     bool ImportTemplateArguments(const TemplateArgument *FromArgs,
                                  unsigned NumFromArgs,
                                SmallVectorImpl<TemplateArgument> &ToArgs);
     bool IsStructuralMatch(RecordDecl *FromRecord, RecordDecl *ToRecord,
                            bool Complain = true);
     bool IsStructuralMatch(VarDecl *FromVar, VarDecl *ToVar,
                            bool Complain = true);
     bool IsStructuralMatch(EnumDecl *FromEnum, EnumDecl *ToRecord);
     bool IsStructuralMatch(EnumConstantDecl *FromEC, EnumConstantDecl *ToEC);
     bool IsStructuralMatch(ClassTemplateDecl *From, ClassTemplateDecl *To);
     bool IsStructuralMatch(VarTemplateDecl *From, VarTemplateDecl *To);
     Decl *VisitDecl(Decl *D);
+    Decl *VisitEmptyDecl(EmptyDecl *D);
     Decl *VisitAccessSpecDecl(AccessSpecDecl *D);
     Decl *VisitStaticAssertDecl(StaticAssertDecl *D);
     Decl *VisitTranslationUnitDecl(TranslationUnitDecl *D);
     Decl *VisitNamespaceDecl(NamespaceDecl *D);
+    Decl *VisitNamespaceAliasDecl(NamespaceAliasDecl *D);
     Decl *VisitTypedefNameDecl(TypedefNameDecl *D, bool IsAlias);
     Decl *VisitTypedefDecl(TypedefDecl *D);
     Decl *VisitTypeAliasDecl(TypeAliasDecl *D);
     Decl *VisitLabelDecl(LabelDecl *D);
     Decl *VisitEnumDecl(EnumDecl *D);
     Decl *VisitRecordDecl(RecordDecl *D);
     Decl *VisitEnumConstantDecl(EnumConstantDecl *D);
     Decl *VisitFunctionDecl(FunctionDecl *D);
     Decl *VisitCXXMethodDecl(CXXMethodDecl *D);
     Decl *VisitCXXConstructorDecl(CXXConstructorDecl *D);
     Decl *VisitCXXDestructorDecl(CXXDestructorDecl *D);
     Decl *VisitCXXConversionDecl(CXXConversionDecl *D);
     Decl *VisitFieldDecl(FieldDecl *D);
     Decl *VisitIndirectFieldDecl(IndirectFieldDecl *D);
     Decl *VisitFriendDecl(FriendDecl *D);
     Decl *VisitObjCIvarDecl(ObjCIvarDecl *D);
     Decl *VisitVarDecl(VarDecl *D);
     Decl *VisitImplicitParamDecl(ImplicitParamDecl *D);
     Decl *VisitParmVarDecl(ParmVarDecl *D);
     Decl *VisitObjCMethodDecl(ObjCMethodDecl *D);
     Decl *VisitObjCTypeParamDecl(ObjCTypeParamDecl *D);
     Decl *VisitObjCCategoryDecl(ObjCCategoryDecl *D);
     Decl *VisitObjCProtocolDecl(ObjCProtocolDecl *D);
     Decl *VisitLinkageSpecDecl(LinkageSpecDecl *D);
+    Decl *VisitUsingDecl(UsingDecl *D);
+    Decl *VisitUsingShadowDecl(UsingShadowDecl *D);
+    Decl *VisitUsingDirectiveDecl(UsingDirectiveDecl *D);
+    Decl *VisitUnresolvedUsingValueDecl(UnresolvedUsingValueDecl *D);
+    Decl *VisitUnresolvedUsingTypenameDecl(UnresolvedUsingTypenameDecl *D);
+
 
     ObjCTypeParamList *ImportObjCTypeParamList(ObjCTypeParamList *list);
     Decl *VisitObjCInterfaceDecl(ObjCInterfaceDecl *D);
     Decl *VisitObjCCategoryImplDecl(ObjCCategoryImplDecl *D);
     Decl *VisitObjCImplementationDecl(ObjCImplementationDecl *D);
     Decl *VisitObjCPropertyDecl(ObjCPropertyDecl *D);
     Decl *VisitObjCPropertyImplDecl(ObjCPropertyImplDecl *D);
     Decl *VisitTemplateTypeParmDecl(TemplateTypeParmDecl *D);
QualType ASTNodeImporter::VisitFunctionProtoType(const FunctionProtoType *T) {
   ToEPI.ExceptionSpec.SourceDecl = cast_or_null<FunctionDecl>(
       Importer.Import(FromEPI.ExceptionSpec.SourceDecl));
   ToEPI.ExceptionSpec.SourceTemplate = cast_or_null<FunctionDecl>(
       Importer.Import(FromEPI.ExceptionSpec.SourceTemplate));
 
   return Importer.getToContext().getFunctionType(ToResultType, ArgTypes, ToEPI);
 }
 
+QualType ASTNodeImporter::VisitUnresolvedUsingType(
+    const UnresolvedUsingType *T) {
+  UnresolvedUsingTypenameDecl *ToD = cast_or_null<UnresolvedUsingTypenameDecl>(
+        Importer.Import(T->getDecl()));
+  if (!ToD)
+    return QualType();
+
+  UnresolvedUsingTypenameDecl *ToPrevD =
+      cast_or_null<UnresolvedUsingTypenameDecl>(
+        Importer.Import(T->getDecl()->getPreviousDecl()));
+  if (!ToPrevD && T->getDecl()->getPreviousDecl())
+    return QualType();
+
+  return Importer.getToContext().getTypeDeclType(ToD, ToPrevD);
+}
+
 QualType ASTNodeImporter::VisitParenType(const ParenType *T) {
   QualType ToInnerType = Importer.Import(T->getInnerType());
   if (ToInnerType.isNull())
     return QualType();
     
   return Importer.getToContext().getParenType(ToInnerType);
 }
 
case TemplateArgument::Pack: {
     return TemplateArgument(
         llvm::makeArrayRef(ToPack).copy(Importer.getToContext()));
   }
   }
   
   llvm_unreachable("Invalid template argument kind");
 }
 
-TemplateArgumentLoc ASTNodeImporter::ImportTemplateArgumentLoc(
-    const TemplateArgumentLoc &TALoc, bool &Error) {
-  Error = false;
+Optional<TemplateArgumentLoc>
+ASTNodeImporter::ImportTemplateArgumentLoc(const TemplateArgumentLoc &TALoc) {
   TemplateArgument Arg = ImportTemplateArgument(TALoc.getArgument());
   TemplateArgumentLocInfo FromInfo = TALoc.getLocInfo();
   TemplateArgumentLocInfo ToInfo;
   if (Arg.getKind() == TemplateArgument::Expression) {
     Expr *E = Importer.Import(FromInfo.getAsExpr());
     ToInfo = TemplateArgumentLocInfo(E);
     if (!E)
-      Error = true;
+      return None;
   } else if (Arg.getKind() == TemplateArgument::Type) {
     if (TypeSourceInfo *TSI = Importer.Import(FromInfo.getAsTypeSourceInfo()))
       ToInfo = TemplateArgumentLocInfo(TSI);
     else
-      Error = true;
+      return None;
   } else {
     ToInfo = TemplateArgumentLocInfo(
           Importer.Import(FromInfo.getTemplateQualifierLoc()),
           Importer.Import(FromInfo.getTemplateNameLoc()),
           Importer.Import(FromInfo.getTemplateEllipsisLoc()));
   }
   return TemplateArgumentLoc(Arg, ToInfo);
 }

 }
 
 Decl *ASTNodeImporter::VisitDecl(Decl *D) {
   Importer.FromDiag(D->getLocation(), diag::err_unsupported_ast_node)
     << D->getDeclKindName();
   return nullptr;
 }
 
+Decl *ASTNodeImporter::VisitEmptyDecl(EmptyDecl *D) {
+  // Import the context of this declaration.
+  DeclContext *DC = Importer.ImportContext(D->getDeclContext());
+  if (!DC)
+    return nullptr;
+
+  DeclContext *LexicalDC = DC;
+  if (D->getDeclContext() != D->getLexicalDeclContext()) {
+    LexicalDC = Importer.ImportContext(D->getLexicalDeclContext());
+    if (!LexicalDC)
+      return nullptr;
+  }
+
+  // Import the location of this declaration.
+  SourceLocation Loc = Importer.Import(D->getLocation());
+
+  EmptyDecl *ToD = EmptyDecl::Create(Importer.getToContext(), DC, Loc);
+  ToD->setLexicalDeclContext(LexicalDC);
+  Importer.Imported(D, ToD);
+  LexicalDC->addDeclInternal(ToD);
+  return ToD;
+}
+
 Decl *ASTNodeImporter::VisitTranslationUnitDecl(TranslationUnitDecl *D) {
   TranslationUnitDecl *ToD = 
     Importer.getToContext().getTranslationUnitDecl();
     
   Importer.Imported(D, ToD);
     
   return ToD;
 }
Decl *ASTNodeImporter::VisitNamespaceDecl(NamespaceDecl *D) {
   }
   Importer.Imported(D, ToNamespace);
   
   ImportDeclContext(D);
   
   return ToNamespace;
 }
 
+Decl *ASTNodeImporter::VisitNamespaceAliasDecl(NamespaceAliasDecl *D) {
+  // Import the major distinguishing characteristics of this namespace.
+  DeclContext *DC, *LexicalDC;
+  DeclarationName Name;
+  SourceLocation Loc;
+  NamedDecl *LookupD;
+  if (ImportDeclParts(D, DC, LexicalDC, Name, LookupD, Loc))
+    return nullptr;
+  if (LookupD)
+    return LookupD;
+
+  // NOTE: No conflict resolution is done for namespace aliases now.
+
+  NamespaceDecl *TargetDecl = cast<NamespaceDecl>(
+        Importer.Import(D->getNamespace()));
+  if (!TargetDecl)
+    return nullptr;
+
+  IdentifierInfo *ToII = Importer.Import(D->getIdentifier());
+  if (!ToII)
+    return nullptr;
+
+  NestedNameSpecifierLoc ToQLoc = Importer.Import(D->getQualifierLoc());
+  if (D->getQualifierLoc() && !ToQLoc)
+    return nullptr;
+
+  NamespaceAliasDecl *ToD = NamespaceAliasDecl::Create(
+        Importer.getToContext(), DC, Importer.Import(D->getNamespaceLoc()),
+        Importer.Import(D->getAliasLoc()), ToII, ToQLoc,
+        Importer.Import(D->getTargetNameLoc()), TargetDecl);
+
+  ToD->setLexicalDeclContext(LexicalDC);
+  Importer.Imported(D, ToD);
+  LexicalDC->addDeclInternal(ToD);
+
+  return ToD;
+}
+
 Decl *ASTNodeImporter::VisitTypedefNameDecl(TypedefNameDecl *D, bool IsAlias) {
   // Import the major distinguishing characteristics of this typedef.
   DeclContext *DC, *LexicalDC;
   DeclarationName Name;
   SourceLocation Loc;
   NamedDecl *ToD;
   if (ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
     return nullptr;
if (CXXRecordDecl *DCXX = llvm::dyn_cast<CXXRecordDecl>(D)) {
       } else {
         D2CXX = CXXRecordDecl::Create(Importer.getToContext(),
                                       D->getTagKind(),
                                       DC, StartLoc, Loc,
                                       Name.getAsIdentifierInfo());
       }
       D2 = D2CXX;
       D2->setAccess(D->getAccess());
+
+      Importer.Imported(D, D2);
+
+      if (ClassTemplateDecl *FromDescribed =
+          DCXX->getDescribedClassTemplate()) {
+        ClassTemplateDecl *ToDescribed = cast_or_null<ClassTemplateDecl>(
+              Importer.Import(FromDescribed));
+        if (!ToDescribed)
+          return nullptr;
+        D2CXX->setDescribedClassTemplate(ToDescribed);
+
+      } else if (MemberSpecializationInfo *MemberInfo =
+                   DCXX->getMemberSpecializationInfo()) {
+        TemplateSpecializationKind SK =
+            MemberInfo->getTemplateSpecializationKind();
+        CXXRecordDecl *FromInst = DCXX->getInstantiatedFromMemberClass();
+        CXXRecordDecl *ToInst =
+            cast_or_null<CXXRecordDecl>(Importer.Import(FromInst));
+        if (FromInst && !ToInst)
+          return nullptr;
+        D2CXX->setInstantiationOfMemberClass(ToInst, SK);
+        D2CXX->getMemberSpecializationInfo()->setPointOfInstantiation(
+              Importer.Import(MemberInfo->getPointOfInstantiation()));
+      }
+
     } else {
       D2 = RecordDecl::Create(Importer.getToContext(), D->getTagKind(),
                               DC, StartLoc, Loc, Name.getAsIdentifierInfo());
     }
     
     D2->setQualifierInfo(Importer.Import(D->getQualifierLoc()));
     D2->setLexicalDeclContext(LexicalDC);
     LexicalDC->addDeclInternal(D2);
Decl *ASTNodeImporter::VisitLinkageSpecDecl(LinkageSpecDecl *D) {
   ToLinkageSpec->setLexicalDeclContext(LexicalDC);
   LexicalDC->addDeclInternal(ToLinkageSpec);
 
   Importer.Imported(D, ToLinkageSpec);
 
   return ToLinkageSpec;
 }
 
+Decl *ASTNodeImporter::VisitUsingDecl(UsingDecl *D) {
+  DeclContext *DC, *LexicalDC;
+  DeclarationName Name;
+  SourceLocation Loc;
+  NamedDecl *ToD = nullptr;
+  if (ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
+    return nullptr;
+  if (ToD)
+    return ToD;
+
+  DeclarationNameInfo NameInfo(Name,
+                               Importer.Import(D->getNameInfo().getLoc()));
+  ImportDeclarationNameLoc(D->getNameInfo(), NameInfo);
+
+  UsingDecl *ToUsing = UsingDecl::Create(Importer.getToContext(), DC,
+                                         Importer.Import(D->getUsingLoc()),
+                                         Importer.Import(D->getQualifierLoc()),
+                                         NameInfo, D->hasTypename());
+  ToUsing->setLexicalDeclContext(LexicalDC);
+  LexicalDC->addDeclInternal(ToUsing);
+  Importer.Imported(D, ToUsing);
+
+  if (NamedDecl *FromPattern =
+      Importer.getFromContext().getInstantiatedFromUsingDecl(D)) {
+    if (NamedDecl *ToPattern =
+        dyn_cast_or_null<NamedDecl>(Importer.Import(FromPattern)))
+      Importer.getToContext().setInstantiatedFromUsingDecl(ToUsing, ToPattern);
+    else
+      return nullptr;
+  }
+
+  for (UsingShadowDecl *FromShadow : D->shadows()) {
+    if (UsingShadowDecl *ToShadow =
+        dyn_cast_or_null<UsingShadowDecl>(Importer.Import(FromShadow)))
+      ToUsing->addShadowDecl(ToShadow);
+    else
+      // FIXME: We return a nullptr here but the definition is already created
+      // and available with lookups. How to fix this?..
+      return nullptr;
+  }
+  return ToUsing;
+}
+
+Decl *ASTNodeImporter::VisitUsingShadowDecl(UsingShadowDecl *D) {
+  DeclContext *DC, *LexicalDC;
+  DeclarationName Name;
+  SourceLocation Loc;
+  NamedDecl *ToD = nullptr;
+  if (ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
+    return nullptr;
+  if (ToD)
+    return ToD;
+
+  UsingDecl *ToUsing = dyn_cast_or_null<UsingDecl>(
+        Importer.Import(D->getUsingDecl()));
+  if (!ToUsing)
+    return nullptr;
+
+  NamedDecl *ToTarget = dyn_cast_or_null<NamedDecl>(
+        Importer.Import(D->getTargetDecl()));
+  if (!ToTarget)
+    return nullptr;
+
+  UsingShadowDecl *ToShadow = UsingShadowDecl::Create(
+        Importer.getToContext(), DC, Loc, ToUsing, ToTarget);
+
+  ToShadow->setLexicalDeclContext(LexicalDC);
+  ToShadow->setAccess(D->getAccess());
+  Importer.Imported(D, ToShadow);
+
+  if (UsingShadowDecl *FromPattern =
+      Importer.getFromContext().getInstantiatedFromUsingShadowDecl(D)) {
+    if (UsingShadowDecl *ToPattern =
+        dyn_cast_or_null<UsingShadowDecl>(Importer.Import(FromPattern)))
+      Importer.getToContext().setInstantiatedFromUsingShadowDecl(ToShadow,
+                                                                 ToPattern);
+    else
+      return nullptr;
+  }
+
+  LexicalDC->addDeclInternal(ToShadow);
+
+  return ToShadow;
+}
+
+
+Decl *ASTNodeImporter::VisitUsingDirectiveDecl(UsingDirectiveDecl *D) {
+  DeclContext *DC, *LexicalDC;
+  DeclarationName Name;
+  SourceLocation Loc;
+  NamedDecl *ToD = nullptr;
+  if (ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
+    return nullptr;
+  if (ToD)
+    return ToD;
+
+  DeclContext *ToComAncestor = Importer.ImportContext(D->getCommonAncestor());
+  if (!ToComAncestor)
+    return nullptr;
+
+  NamespaceDecl *ToNominated = cast_or_null<NamespaceDecl>(
+        Importer.Import(D->getNominatedNamespace()));
+  if (!ToNominated)
+    return nullptr;
+
+  UsingDirectiveDecl *ToUsingDir = UsingDirectiveDecl::Create(
+        Importer.getToContext(), DC, Importer.Import(D->getUsingLoc()),
+        Importer.Import(D->getNamespaceKeyLocation()),
+        Importer.Import(D->getQualifierLoc()),
+        Importer.Import(D->getIdentLocation()), ToNominated, ToComAncestor);
+  ToUsingDir->setLexicalDeclContext(LexicalDC);
+  LexicalDC->addDeclInternal(ToUsingDir);
+  Importer.Imported(D, ToUsingDir);
+
+  return ToUsingDir;
+}
+
+Decl *ASTNodeImporter::VisitUnresolvedUsingValueDecl(
+    UnresolvedUsingValueDecl *D) {
+  DeclContext *DC, *LexicalDC;
+  DeclarationName Name;
+  SourceLocation Loc;
+  NamedDecl *ToD = nullptr;
+  if (ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
+    return nullptr;
+  if (ToD)
+    return ToD;
+
+  DeclarationNameInfo NameInfo(Name, Importer.Import(D->getNameInfo().getLoc()));
+  ImportDeclarationNameLoc(D->getNameInfo(), NameInfo);
+
+  UnresolvedUsingValueDecl *ToUsingValue = UnresolvedUsingValueDecl::Create(
+        Importer.getToContext(), DC, Importer.Import(D->getUsingLoc()),
+        Importer.Import(D->getQualifierLoc()), NameInfo,
+        Importer.Import(D->getEllipsisLoc()));
+
+  Importer.Imported(D, ToUsingValue);
+  ToUsingValue->setAccess(D->getAccess());
+  ToUsingValue->setLexicalDeclContext(LexicalDC);
+  LexicalDC->addDeclInternal(ToUsingValue);
+
+  return ToUsingValue;
+}
+
+Decl *ASTNodeImporter::VisitUnresolvedUsingTypenameDecl(
+    UnresolvedUsingTypenameDecl *D) {
+  DeclContext *DC, *LexicalDC;
+  DeclarationName Name;
+  SourceLocation Loc;
+  NamedDecl *ToD = nullptr;
+  if (ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
+    return nullptr;
+  if (ToD)
+    return ToD;
+
+  UnresolvedUsingTypenameDecl *ToUsing = UnresolvedUsingTypenameDecl::Create(
+        Importer.getToContext(), DC, Importer.Import(D->getUsingLoc()),
+        Importer.Import(D->getTypenameLoc()),
+        Importer.Import(D->getQualifierLoc()), Loc, Name,
+        Importer.Import(D->getEllipsisLoc()));
+
+  Importer.Imported(D, ToUsing);
+  ToUsing->setAccess(D->getAccess());
+  ToUsing->setLexicalDeclContext(LexicalDC);
+  LexicalDC->addDeclInternal(ToUsing);
+
+  return ToUsing;
+}
+
+
 bool ASTNodeImporter::ImportDefinition(ObjCInterfaceDecl *From, 
                                        ObjCInterfaceDecl *To,
                                        ImportDefinitionKind Kind) {
   if (To->getDefinition()) {
     // Check consistency of superclass.
     ObjCInterfaceDecl *FromSuper = From->getSuperClass();
     if (FromSuper) {
       FromSuper = cast_or_null<ObjCInterfaceDecl>(Importer.Import(FromSuper));
if (!DC->isFunctionOrMethod()) {
     
     if (!Name)
       return nullptr;
   }
 
   CXXRecordDecl *DTemplated = D->getTemplatedDecl();
   
   // Create the declaration that is being templated.
-  // Create the declaration that is being templated.
   CXXRecordDecl *D2Templated = cast_or_null<CXXRecordDecl>(
         Importer.Import(DTemplated));
   if (!D2Templated)
     return nullptr;
 
   // Resolve possible cyclic import.
   if (Decl *AlreadyImported = Importer.GetAlreadyImportedOrNull(D))
     return AlreadyImported;
if (D2) {
     // Create a new specialization.
     if (ClassTemplatePartialSpecializationDecl *PartialSpec =
         dyn_cast<ClassTemplatePartialSpecializationDecl>(D)) {
 
       // Import TemplateArgumentListInfo
       TemplateArgumentListInfo ToTAInfo;
       auto &ASTTemplateArgs = *PartialSpec->getTemplateArgsAsWritten();
       for (unsigned I = 0, E = ASTTemplateArgs.NumTemplateArgs; I < E; ++I) {
-        bool Error = false;
-        auto ToLoc = ImportTemplateArgumentLoc(ASTTemplateArgs[I], Error);
-        if (Error)
+        if (auto ToLoc = ImportTemplateArgumentLoc(ASTTemplateArgs[I]))
+          ToTAInfo.addArgument(*ToLoc);
+        else
           return nullptr;
-        ToTAInfo.addArgument(ToLoc);
       }
 
       QualType CanonInjType = Importer.Import(
             PartialSpec->getInjectedSpecializationType());
       if (CanonInjType.isNull())
         return nullptr;
       CanonInjType = CanonInjType.getCanonicalType();
 
Expr *ASTNodeImporter::VisitDeclRefExpr(DeclRefExpr *E) {
   if (T.isNull())
     return nullptr;
 
 
   TemplateArgumentListInfo ToTAInfo;
   TemplateArgumentListInfo *ResInfo = nullptr;
   if (E->hasExplicitTemplateArgs()) {
     for (const auto &FromLoc : E->template_arguments()) {
-      bool Error = false;
-      TemplateArgumentLoc ToTALoc = ImportTemplateArgumentLoc(FromLoc, Error);
-      if (Error)
+      if (auto ToTALoc = ImportTemplateArgumentLoc(FromLoc))
+        ToTAInfo.addArgument(*ToTALoc);
+      else
         return nullptr;
-      ToTAInfo.addArgument(ToTALoc);
     }
     ResInfo = &ToTAInfo;
   }
 
   DeclRefExpr *DRE = DeclRefExpr::Create(Importer.getToContext(), 
                                          Importer.Import(E->getQualifierLoc()),
                                    Importer.Import(E->getTemplateKeywordLoc()),
                                          ToD,

test/ASTMerge/namespace/Inputs/namespace1.cpp

 namespace N2 {
   extern float y;
 }
 
 // Merge namespace with conflict
 namespace N3 {
   extern float z;
 }
+
+namespace AliasWithSameName = N3;
+
+namespace TestUnresolvedTypenameAndValueDecls {
+template <class T> class Base {
+public:
+  typedef T foo;
+  void bar();
+};
+}

test/ASTMerge/namespace/Inputs/namespace2.cpp

 namespace N2 {
   extern float y;
 }
 
 // Merge namespace with conflict
 namespace N3 {
   extern double z;
 }
+
+namespace Enclosing {
+namespace Nested {
+  const int z = 4;
+}
+}
+
+namespace ContainsInline {
+  inline namespace Inline {
+    const int z = 10;
+  }
+}
+
+namespace TestAliasName = Enclosing::Nested;
+// NOTE: There is no warning on this alias.
+namespace AliasWithSameName = Enclosing::Nested;
+
+namespace TestUsingDecls {
+
+namespace A {
+void foo();
+}
+namespace B {
+using A::foo; // <- a UsingDecl creating a UsingShadow
+}
+
+}// end namespace TestUsingDecls
+
+namespace TestUnresolvedTypenameAndValueDecls {
+
+template <class T> class Base;
+template <class T> class Derived : public Base<T> {
+public:
+  using typename Base<T>::foo;
+  using Base<T>::bar;
+  typedef typename Derived::foo NewUnresolvedUsingType;
+};
+
+} // end namespace TestUnresolvedTypenameAndValueDecls
+
+namespace TestUsingNamespace {
+  using namespace Enclosing;
+}

test/ASTMerge/namespace/test.cpp

-// RUN: %clang_cc1 -emit-pch -o %t.1.ast %S/Inputs/namespace1.cpp
-// RUN: %clang_cc1 -emit-pch -o %t.2.ast %S/Inputs/namespace2.cpp
-// RUN: not %clang_cc1 -ast-merge %t.1.ast -ast-merge %t.2.ast -fsyntax-only %s 2>&1 | FileCheck %s
+// RUN: %clang_cc1 -emit-pch -std=c++1z -o %t.1.ast %S/Inputs/namespace1.cpp
+// RUN: %clang_cc1 -emit-pch -std=c++1z -o %t.2.ast %S/Inputs/namespace2.cpp
+// RUN: not %clang_cc1 -std=c++1z -ast-merge %t.1.ast -ast-merge %t.2.ast -fsyntax-only %s 2>&1 | FileCheck %s
+
+static_assert(TestAliasName::z == 4);
+static_assert(ContainsInline::z == 10);
+
+void testImport() {
+  typedef TestUnresolvedTypenameAndValueDecls::Derived<int> Imported;
+  Imported a; // Successfull instantiation
+  static_assert(sizeof(Imported::foo) == sizeof(int));
+  static_assert(sizeof(TestUnresolvedTypenameAndValueDecls::Derived<double>::NewUnresolvedUsingType) == sizeof(double));
+}
+
 
 // CHECK: namespace2.cpp:16:17: error: external variable 'z' declared with incompatible types in different translation units ('double' vs. 'float')
 // CHECK: namespace1.cpp:16:16: note: declared here with type 'float'