[ASTImporter] Support LambdaExprs and improve template support

Also, a number of style and bug fixes was done:

 *  ASTImporterTest: added sanity check for source node
 *  ExternalASTMerger: better lookup for template specializations
 *  ASTImporter: don't add templated declarations into DeclContext
 *  ASTImporter: introduce a helper, ImportTemplateArgumentListInfo getting SourceLocations
 *  ASTImporter: proper set ParmVarDecls for imported FunctionProtoTypeLoc

Differential Revision: https://reviews.llvm.org/D42301

llvm-svn: 323519

3 files changed, 334 insertions, 61 deletions

diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 27b6ff1c516..aea044c8c49 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -97,6 +97,8 @@ namespace clang {
     typedef DesignatedInitExpr::Designator Designator;
     Designator ImportDesignator(const Designator &D);
 
+    Optional<LambdaCapture> ImportLambdaCapture(const LambdaCapture &From);
+
                         
     /// \brief What we should import from the definition.
     enum ImportDefinitionKind { 
@@ -127,16 +129,26 @@ namespace clang {
     bool ImportDefinition(ObjCProtocolDecl *From, ObjCProtocolDecl *To,
                           ImportDefinitionKind Kind = IDK_Default);
     TemplateParameterList *ImportTemplateParameterList(
-                                                 TemplateParameterList *Params);
+        TemplateParameterList *Params);
     TemplateArgument ImportTemplateArgument(const TemplateArgument &From);
     Optional<TemplateArgumentLoc> ImportTemplateArgumentLoc(
         const TemplateArgumentLoc &TALoc);
     bool ImportTemplateArguments(const TemplateArgument *FromArgs,
                                  unsigned NumFromArgs,
-                               SmallVectorImpl<TemplateArgument> &ToArgs);
+                                 SmallVectorImpl<TemplateArgument> &ToArgs);
+
     template <typename InContainerTy>
     bool ImportTemplateArgumentListInfo(const InContainerTy &Container,
                                         TemplateArgumentListInfo &ToTAInfo);
+
+    template<typename InContainerTy>
+    bool ImportTemplateArgumentListInfo(SourceLocation FromLAngleLoc,
+                                        SourceLocation FromRAngleLoc,
+                                        const InContainerTy &Container,
+                                        TemplateArgumentListInfo &Result);
+
+    bool ImportTemplateInformation(FunctionDecl *FromFD, FunctionDecl *ToFD);
+
     bool IsStructuralMatch(RecordDecl *FromRecord, RecordDecl *ToRecord,
                            bool Complain = true);
     bool IsStructuralMatch(VarDecl *FromVar, VarDecl *ToVar,
@@ -295,6 +307,7 @@ namespace clang {
     Expr *VisitCXXPseudoDestructorExpr(CXXPseudoDestructorExpr *E);
     Expr *VisitMemberExpr(MemberExpr *E);
     Expr *VisitCallExpr(CallExpr *E);
+    Expr *VisitLambdaExpr(LambdaExpr *LE);
     Expr *VisitInitListExpr(InitListExpr *E);
     Expr *VisitArrayInitLoopExpr(ArrayInitLoopExpr *E);
     Expr *VisitArrayInitIndexExpr(ArrayInitIndexExpr *E);
@@ -1045,7 +1058,6 @@ bool ASTNodeImporter::ImportDefinition(RecordDecl *From, RecordDecl *To,
       = FromData.HasDeclaredCopyConstructorWithConstParam;
     ToData.HasDeclaredCopyAssignmentWithConstParam
       = FromData.HasDeclaredCopyAssignmentWithConstParam;
-    ToData.IsLambda = FromData.IsLambda;
 
     SmallVector<CXXBaseSpecifier *, 4> Bases;
     for (const auto &Base1 : FromCXX->bases()) {
@@ -1256,6 +1268,9 @@ bool ASTNodeImporter::ImportTemplateArguments(const TemplateArgument *FromArgs,
   return false;
 }
 
+// We cannot use Optional<> pattern here and below because
+// TemplateArgumentListInfo's operator new is declared as deleted so it cannot
+// be stored in Optional.
 template <typename InContainerTy>
 bool ASTNodeImporter::ImportTemplateArgumentListInfo(
     const InContainerTy &Container, TemplateArgumentListInfo &ToTAInfo) {
@@ -1268,6 +1283,18 @@ bool ASTNodeImporter::ImportTemplateArgumentListInfo(
   return false;
 }
 
+template <typename InContainerTy>
+bool ASTNodeImporter::ImportTemplateArgumentListInfo(
+    SourceLocation FromLAngleLoc, SourceLocation FromRAngleLoc,
+    const InContainerTy &Container, TemplateArgumentListInfo &Result) {
+  TemplateArgumentListInfo ToTAInfo(Importer.Import(FromLAngleLoc),
+                                    Importer.Import(FromRAngleLoc));
+  if (ImportTemplateArgumentListInfo(Container, ToTAInfo))
+    return true;
+  Result = ToTAInfo;
+  return false;
+}
+
 bool ASTNodeImporter::IsStructuralMatch(RecordDecl *FromRecord, 
                                         RecordDecl *ToRecord, bool Complain) {
   // Eliminate a potential failure point where we attempt to re-import
@@ -1918,16 +1945,16 @@ Decl *ASTNodeImporter::VisitRecordDecl(RecordDecl *D) {
         if (DCXX->getLambdaContextDecl() && !CDecl)
           return nullptr;
         D2CXX->setLambdaMangling(DCXX->getLambdaManglingNumber(), CDecl);
-      } else if (DCXX->isInjectedClassName()) {                                                 
-        // We have to be careful to do a similar dance to the one in                            
-        // Sema::ActOnStartCXXMemberDeclarations                                                
-        CXXRecordDecl *const PrevDecl = nullptr;                                                
-        const bool DelayTypeCreation = true;                                                    
-        D2CXX = CXXRecordDecl::Create(                                                          
-            Importer.getToContext(), D->getTagKind(), DC, StartLoc, Loc,                        
-            Name.getAsIdentifierInfo(), PrevDecl, DelayTypeCreation);                           
-        Importer.getToContext().getTypeDeclType(                                                
-            D2CXX, llvm::dyn_cast<CXXRecordDecl>(DC));                                          
+      } else if (DCXX->isInjectedClassName()) {
+        // We have to be careful to do a similar dance to the one in
+        // Sema::ActOnStartCXXMemberDeclarations
+        CXXRecordDecl *const PrevDecl = nullptr;
+        const bool DelayTypeCreation = true;
+        D2CXX = CXXRecordDecl::Create(
+            Importer.getToContext(), D->getTagKind(), DC, StartLoc, Loc,
+            Name.getAsIdentifierInfo(), PrevDecl, DelayTypeCreation);
+        Importer.getToContext().getTypeDeclType(
+            D2CXX, llvm::dyn_cast<CXXRecordDecl>(DC));
       } else {
         D2CXX = CXXRecordDecl::Create(Importer.getToContext(),
                                       D->getTagKind(),
@@ -1936,6 +1963,9 @@ Decl *ASTNodeImporter::VisitRecordDecl(RecordDecl *D) {
       }
       D2 = D2CXX;
       D2->setAccess(D->getAccess());
+      D2->setLexicalDeclContext(LexicalDC);
+      if (!DCXX->getDescribedClassTemplate())
+        LexicalDC->addDeclInternal(D2);
 
       Importer.Imported(D, D2);
 
@@ -1964,11 +1994,11 @@ Decl *ASTNodeImporter::VisitRecordDecl(RecordDecl *D) {
     } else {
       D2 = RecordDecl::Create(Importer.getToContext(), D->getTagKind(),
                               DC, StartLoc, Loc, Name.getAsIdentifierInfo());
+      D2->setLexicalDeclContext(LexicalDC);
+      LexicalDC->addDeclInternal(D2);
     }
     
     D2->setQualifierInfo(Importer.Import(D->getQualifierLoc()));
-    D2->setLexicalDeclContext(LexicalDC);
-    LexicalDC->addDeclInternal(D2);
     if (D->isAnonymousStructOrUnion())
       D2->setAnonymousStructOrUnion(true);
     if (PrevDecl) {
@@ -2044,6 +2074,94 @@ Decl *ASTNodeImporter::VisitEnumConstantDecl(EnumConstantDecl *D) {
   return ToEnumerator;
 }
 
+bool ASTNodeImporter::ImportTemplateInformation(FunctionDecl *FromFD,
+                                                FunctionDecl *ToFD) {
+  switch (FromFD->getTemplatedKind()) {
+  case FunctionDecl::TK_NonTemplate:
+  case FunctionDecl::TK_FunctionTemplate:
+    break;
+
+  case FunctionDecl::TK_MemberSpecialization: {
+    auto *InstFD = cast_or_null<FunctionDecl>(
+          Importer.Import(FromFD->getInstantiatedFromMemberFunction()));
+    if (!InstFD)
+      return true;
+
+    TemplateSpecializationKind TSK = FromFD->getTemplateSpecializationKind();
+    SourceLocation POI = Importer.Import(
+          FromFD->getMemberSpecializationInfo()->getPointOfInstantiation());
+    ToFD->setInstantiationOfMemberFunction(InstFD, TSK);
+    ToFD->getMemberSpecializationInfo()->setPointOfInstantiation(POI);
+    break;
+  }
+
+  case FunctionDecl::TK_FunctionTemplateSpecialization: {
+    auto *FTSInfo = FromFD->getTemplateSpecializationInfo();
+    auto *Template = cast_or_null<FunctionTemplateDecl>(
+        Importer.Import(FTSInfo->getTemplate()));
+    if (!Template)
+      return true;
+    TemplateSpecializationKind TSK = FTSInfo->getTemplateSpecializationKind();
+
+    // Import template arguments.
+    auto TemplArgs = FTSInfo->TemplateArguments->asArray();
+    SmallVector<TemplateArgument, 8> ToTemplArgs;
+    if (ImportTemplateArguments(TemplArgs.data(), TemplArgs.size(),
+                                ToTemplArgs))
+      return true;
+
+    TemplateArgumentList *ToTAList = TemplateArgumentList::CreateCopy(
+          Importer.getToContext(), ToTemplArgs);
+
+    TemplateArgumentListInfo ToTAInfo;
+    const auto *FromTAArgsAsWritten = FTSInfo->TemplateArgumentsAsWritten;
+    if (FromTAArgsAsWritten) {
+      if (ImportTemplateArgumentListInfo(
+              FromTAArgsAsWritten->LAngleLoc, FromTAArgsAsWritten->RAngleLoc,
+              FromTAArgsAsWritten->arguments(), ToTAInfo))
+        return true;
+    }
+
+    SourceLocation POI = Importer.Import(FTSInfo->getPointOfInstantiation());
+
+    ToFD->setFunctionTemplateSpecialization(
+        Template, ToTAList, /* InsertPos= */ nullptr,
+        TSK, FromTAArgsAsWritten ? &ToTAInfo : nullptr, POI);
+    break;
+  }
+
+  case FunctionDecl::TK_DependentFunctionTemplateSpecialization: {
+    auto *FromInfo = FromFD->getDependentSpecializationInfo();
+    UnresolvedSet<8> TemplDecls;
+    unsigned NumTemplates = FromInfo->getNumTemplates();
+    for (unsigned I = 0; I < NumTemplates; I++) {
+      if (auto *ToFTD = cast_or_null<FunctionTemplateDecl>(
+              Importer.Import(FromInfo->getTemplate(I))))
+        TemplDecls.addDecl(ToFTD);
+      else
+        return true;
+    }
+
+    // Import TemplateArgumentListInfo.
+    TemplateArgumentListInfo ToTAInfo;
+    if (ImportTemplateArgumentListInfo(
+            FromInfo->getLAngleLoc(), FromInfo->getRAngleLoc(),
+            llvm::makeArrayRef(FromInfo->getTemplateArgs(),
+                               FromInfo->getNumTemplateArgs()),
+            ToTAInfo))
+      return true;
+
+    ToFD->setDependentTemplateSpecialization(Importer.getToContext(),
+                                             TemplDecls, ToTAInfo);
+    break;
+  }
+  default:
+    llvm_unreachable("All cases should be covered!");
+  }
+
+  return false;
+}
+
 Decl *ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {
   // Import the major distinguishing characteristics of this function.
   DeclContext *DC, *LexicalDC;
@@ -2151,15 +2269,18 @@ Decl *ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {
     Parameters.push_back(ToP);
   }
   
-  // Create the imported function.
   TypeSourceInfo *TInfo = Importer.Import(D->getTypeSourceInfo());
+  if (D->getTypeSourceInfo() && !TInfo)
+    return nullptr;
+
+  // Create the imported function.
   FunctionDecl *ToFunction = nullptr;
   SourceLocation InnerLocStart = Importer.Import(D->getInnerLocStart());
   if (CXXConstructorDecl *FromConstructor = dyn_cast<CXXConstructorDecl>(D)) {
     ToFunction = CXXConstructorDecl::Create(Importer.getToContext(),
                                             cast<CXXRecordDecl>(DC),
                                             InnerLocStart,
-                                            NameInfo, T, TInfo, 
+                                            NameInfo, T, TInfo,
                                             FromConstructor->isExplicit(),
                                             D->isInlineSpecified(), 
                                             D->isImplicit(),
@@ -2225,9 +2346,9 @@ Decl *ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {
   Importer.Imported(D, ToFunction);
 
   // Set the parameters.
-  for (unsigned I = 0, N = Parameters.size(); I != N; ++I) {
-    Parameters[I]->setOwningFunction(ToFunction);
-    ToFunction->addDeclInternal(Parameters[I]);
+  for (ParmVarDecl *Param : Parameters) {
+    Param->setOwningFunction(ToFunction);
+    ToFunction->addDeclInternal(Param);
   }
   ToFunction->setParams(Parameters);
 
@@ -2237,6 +2358,16 @@ Decl *ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {
     ToFunction->setPreviousDecl(Recent);
   }
 
+  // We need to complete creation of FunctionProtoTypeLoc manually with setting
+  // params it refers to.
+  if (TInfo) {
+    if (auto ProtoLoc =
+        TInfo->getTypeLoc().IgnoreParens().getAs<FunctionProtoTypeLoc>()) {
+      for (unsigned I = 0, N = Parameters.size(); I != N; ++I)
+        ProtoLoc.setParam(I, Parameters[I]);
+    }
+  }
+
   if (usedDifferentExceptionSpec) {
     // Update FunctionProtoType::ExtProtoInfo.
     QualType T = Importer.Import(D->getType());
@@ -2254,8 +2385,17 @@ Decl *ASTNodeImporter::VisitFunctionDecl(FunctionDecl *D) {
 
   // FIXME: Other bits to merge?
 
+  // If it is a template, import all related things.
+  if (ImportTemplateInformation(D, ToFunction))
+    return nullptr;
+
   // Add this function to the lexical context.
-  LexicalDC->addDeclInternal(ToFunction);
+  // NOTE: If the function is templated declaration, it should be not added into
+  // LexicalDC. But described template is imported during import of
+  // FunctionTemplateDecl (it happens later). So, we use source declaration
+  // to determine if we should add the result function.
+  if (!D->getDescribedFunctionTemplate())
+    LexicalDC->addDeclInternal(ToFunction);
 
   if (auto *FromCXXMethod = dyn_cast<CXXMethodDecl>(D))
     ImportOverrides(cast<CXXMethodDecl>(ToFunction), FromCXXMethod);
@@ -2749,6 +2889,14 @@ Decl *ASTNodeImporter::VisitParmVarDecl(ParmVarDecl *D) {
   if (FromDefArg && !ToDefArg)
     return nullptr;
 
+  if (D->isObjCMethodParameter()) {
+    ToParm->setObjCMethodScopeInfo(D->getFunctionScopeIndex());
+    ToParm->setObjCDeclQualifier(D->getObjCDeclQualifier());
+  } else {
+    ToParm->setScopeInfo(D->getFunctionScopeDepth(),
+                         D->getFunctionScopeIndex());
+  }
+
   if (D->isUsed())
     ToParm->setIsUsed();
 
@@ -3850,12 +3998,12 @@ Decl *ASTNodeImporter::VisitClassTemplateDecl(ClassTemplateDecl *D) {
       return nullptr;
   }
 
-  CXXRecordDecl *DTemplated = D->getTemplatedDecl();
-  
+  CXXRecordDecl *FromTemplated = D->getTemplatedDecl();
+
   // Create the declaration that is being templated.
-  CXXRecordDecl *D2Templated = cast_or_null<CXXRecordDecl>(
-        Importer.Import(DTemplated));
-  if (!D2Templated)
+  CXXRecordDecl *ToTemplated = cast_or_null<CXXRecordDecl>(
+        Importer.Import(FromTemplated));
+  if (!ToTemplated)
     return nullptr;
 
   // Resolve possible cyclic import.
@@ -3863,15 +4011,15 @@ Decl *ASTNodeImporter::VisitClassTemplateDecl(ClassTemplateDecl *D) {
     return AlreadyImported;
 
   // Create the class template declaration itself.
-  TemplateParameterList *TemplateParams
-    = ImportTemplateParameterList(D->getTemplateParameters());
+  TemplateParameterList *TemplateParams =
+      ImportTemplateParameterList(D->getTemplateParameters());
   if (!TemplateParams)
     return nullptr;
 
   ClassTemplateDecl *D2 = ClassTemplateDecl::Create(Importer.getToContext(), DC, 
                                                     Loc, Name, TemplateParams, 
-                                                    D2Templated);
-  D2Templated->setDescribedClassTemplate(D2);    
+                                                    ToTemplated);
+  ToTemplated->setDescribedClassTemplate(D2);
   
   D2->setAccess(D->getAccess());
   D2->setLexicalDeclContext(LexicalDC);
@@ -3879,10 +4027,10 @@ Decl *ASTNodeImporter::VisitClassTemplateDecl(ClassTemplateDecl *D) {
   
   // Note the relationship between the class templates.
   Importer.Imported(D, D2);
-  Importer.Imported(DTemplated, D2Templated);
+  Importer.Imported(FromTemplated, ToTemplated);
 
-  if (DTemplated->isCompleteDefinition() &&
-      !D2Templated->isCompleteDefinition()) {
+  if (FromTemplated->isCompleteDefinition() &&
+      !ToTemplated->isCompleteDefinition()) {
     // FIXME: Import definition!
   }
   
@@ -3958,12 +4106,8 @@ Decl *ASTNodeImporter::VisitClassTemplateSpecializationDecl(
       // Import TemplateArgumentListInfo
       TemplateArgumentListInfo ToTAInfo;
       auto &ASTTemplateArgs = *PartialSpec->getTemplateArgsAsWritten();
-      for (unsigned I = 0, E = ASTTemplateArgs.NumTemplateArgs; I < E; ++I) {
-        if (auto ToLoc = ImportTemplateArgumentLoc(ASTTemplateArgs[I]))
-          ToTAInfo.addArgument(*ToLoc);
-        else
-          return nullptr;
-      }
+      if (ImportTemplateArgumentListInfo(ASTTemplateArgs.arguments(), ToTAInfo))
+        return nullptr;
 
       QualType CanonInjType = Importer.Import(
             PartialSpec->getInjectedSpecializationType());
@@ -4901,12 +5045,8 @@ Expr *ASTNodeImporter::VisitDeclRefExpr(DeclRefExpr *E) {
   TemplateArgumentListInfo ToTAInfo;
   TemplateArgumentListInfo *ResInfo = nullptr;
   if (E->hasExplicitTemplateArgs()) {
-    for (const auto &FromLoc : E->template_arguments()) {
-      if (auto ToTALoc = ImportTemplateArgumentLoc(FromLoc))
-        ToTAInfo.addArgument(*ToTALoc);
-      else
-        return nullptr;
-    }
+    if (ImportTemplateArgumentListInfo(E->template_arguments(), ToTAInfo))
+      return nullptr;
     ResInfo = &ToTAInfo;
   }
 
@@ -5861,11 +6001,10 @@ Expr *ASTNodeImporter::VisitCXXDependentScopeMemberExpr(
   if (BaseType.isNull())
     return nullptr;
 
-  TemplateArgumentListInfo ToTAInfo(Importer.Import(E->getLAngleLoc()),
-                                    Importer.Import(E->getRAngleLoc()));
-  TemplateArgumentListInfo *ResInfo = nullptr;
+  TemplateArgumentListInfo ToTAInfo, *ResInfo = nullptr;
   if (E->hasExplicitTemplateArgs()) {
-    if (ImportTemplateArgumentListInfo(E->template_arguments(), ToTAInfo))
+    if (ImportTemplateArgumentListInfo(E->getLAngleLoc(), E->getRAngleLoc(),
+                                       E->template_arguments(), ToTAInfo))
       return nullptr;
     ResInfo = &ToTAInfo;
   }
@@ -5926,11 +6065,10 @@ Expr *ASTNodeImporter::VisitUnresolvedLookupExpr(UnresolvedLookupExpr *E) {
       return nullptr;
   }
 
-  TemplateArgumentListInfo ToTAInfo(Importer.Import(E->getLAngleLoc()),
-                                    Importer.Import(E->getRAngleLoc()));
-  TemplateArgumentListInfo *ResInfo = nullptr;
+  TemplateArgumentListInfo ToTAInfo, *ResInfo = nullptr;
   if (E->hasExplicitTemplateArgs()) {
-    if (ImportTemplateArgumentListInfo(E->template_arguments(), ToTAInfo))
+    if (ImportTemplateArgumentListInfo(E->getLAngleLoc(), E->getRAngleLoc(),
+                                       E->template_arguments(), ToTAInfo))
       return nullptr;
     ResInfo = &ToTAInfo;
   }
@@ -5981,6 +6119,73 @@ Expr *ASTNodeImporter::VisitCallExpr(CallExpr *E) {
              Importer.Import(E->getRParenLoc()));
 }
 
+Optional<LambdaCapture>
+ASTNodeImporter::ImportLambdaCapture(const LambdaCapture &From) {
+  VarDecl *Var = nullptr;
+  if (From.capturesVariable()) {
+    Var = cast_or_null<VarDecl>(Importer.Import(From.getCapturedVar()));
+    if (!Var)
+      return None;
+  }
+
+  return LambdaCapture(Importer.Import(From.getLocation()), From.isImplicit(),
+                       From.getCaptureKind(), Var,
+                       From.isPackExpansion()
+                         ? Importer.Import(From.getEllipsisLoc())
+                         : SourceLocation());
+}
+
+Expr *ASTNodeImporter::VisitLambdaExpr(LambdaExpr *LE) {
+  CXXRecordDecl *FromClass = LE->getLambdaClass();
+  auto *ToClass = dyn_cast_or_null<CXXRecordDecl>(Importer.Import(FromClass));
+  if (!ToClass)
+    return nullptr;
+
+  // NOTE: lambda classes are created with BeingDefined flag set up.
+  // It means that ImportDefinition doesn't work for them and we should fill it
+  // manually.
+  if (ToClass->isBeingDefined()) {
+    for (auto FromField : FromClass->fields()) {
+      auto *ToField = cast_or_null<FieldDecl>(Importer.Import(FromField));
+      if (!ToField)
+        return nullptr;
+    }
+  }
+
+  auto *ToCallOp = dyn_cast_or_null<CXXMethodDecl>(
+        Importer.Import(LE->getCallOperator()));
+  if (!ToCallOp)
+    return nullptr;
+
+  ToClass->completeDefinition();
+
+  unsigned NumCaptures = LE->capture_size();
+  SmallVector<LambdaCapture, 8> Captures;
+  Captures.reserve(NumCaptures);
+  for (const auto &FromCapture : LE->captures()) {
+    if (auto ToCapture = ImportLambdaCapture(FromCapture))
+      Captures.push_back(*ToCapture);
+    else
+      return nullptr;
+  }
+
+  SmallVector<Expr *, 8> InitCaptures(NumCaptures);
+  if (ImportContainerChecked(LE->capture_inits(), InitCaptures))
+    return nullptr;
+
+  return LambdaExpr::Create(Importer.getToContext(), ToClass,
+                            Importer.Import(LE->getIntroducerRange()),
+                            LE->getCaptureDefault(),
+                            Importer.Import(LE->getCaptureDefaultLoc()),
+                            Captures,
+                            LE->hasExplicitParameters(),
+                            LE->hasExplicitResultType(),
+                            InitCaptures,
+                            Importer.Import(LE->getLocEnd()),
+                            LE->containsUnexpandedParameterPack());
+}
+
+
 Expr *ASTNodeImporter::VisitInitListExpr(InitListExpr *ILE) {
   QualType T = Importer.Import(ILE->getType());
   if (T.isNull())
diff --git a/clang/lib/AST/ASTStructuralEquivalence.cpp b/clang/lib/AST/ASTStructuralEquivalence.cpp
index 0df8e5653f3..a563c7e2fa0 100644
--- a/clang/lib/AST/ASTStructuralEquivalence.cpp
+++ b/clang/lib/AST/ASTStructuralEquivalence.cpp
@@ -1153,12 +1153,22 @@ static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
                                   D2->getTemplateParameters());
 }
 
+static bool IsTemplateDeclCommonStructurallyEquivalent(
+    StructuralEquivalenceContext &Ctx, TemplateDecl *D1, TemplateDecl *D2) {
+  if (!IsStructurallyEquivalent(D1->getIdentifier(), D2->getIdentifier()))
+    return false;
+  if (!D1->getIdentifier()) // Special name
+    if (D1->getNameAsString() != D2->getNameAsString())
+      return false;
+  return IsStructurallyEquivalent(Ctx, D1->getTemplateParameters(),
+                                  D2->getTemplateParameters());
+}
+
 static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
                                      ClassTemplateDecl *D1,
                                      ClassTemplateDecl *D2) {
   // Check template parameters.
-  if (!IsStructurallyEquivalent(Context, D1->getTemplateParameters(),
-                                D2->getTemplateParameters()))
+  if (!IsTemplateDeclCommonStructurallyEquivalent(Context, D1, D2))
     return false;
 
   // Check the templated declaration.
@@ -1166,6 +1176,18 @@ static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
                                           D2->getTemplatedDecl());
 }
 
+static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
+                                     FunctionTemplateDecl *D1,
+                                     FunctionTemplateDecl *D2) {
+  // Check template parameters.
+  if (!IsTemplateDeclCommonStructurallyEquivalent(Context, D1, D2))
+    return false;
+
+  // Check the templated declaration.
+  return Context.IsStructurallyEquivalent(D1->getTemplatedDecl()->getType(),
+                                          D2->getTemplatedDecl()->getType());
+}
+
 /// Determine structural equivalence of two declarations.
 static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
                                      Decl *D1, Decl *D2) {
@@ -1293,6 +1315,7 @@ bool StructuralEquivalenceContext::Finish() {
         // Record/non-record mismatch.
         Equivalent = false;
       }
+
     } else if (EnumDecl *Enum1 = dyn_cast<EnumDecl>(D1)) {
       if (EnumDecl *Enum2 = dyn_cast<EnumDecl>(D2)) {
         // Check for equivalent enum names.
@@ -1309,6 +1332,7 @@ bool StructuralEquivalenceContext::Finish() {
         // Enum/non-enum mismatch
         Equivalent = false;
       }
+
     } else if (TypedefNameDecl *Typedef1 = dyn_cast<TypedefNameDecl>(D1)) {
       if (TypedefNameDecl *Typedef2 = dyn_cast<TypedefNameDecl>(D2)) {
         if (!::IsStructurallyEquivalent(Typedef1->getIdentifier(),
@@ -1320,17 +1344,30 @@ bool StructuralEquivalenceContext::Finish() {
         // Typedef/non-typedef mismatch.
         Equivalent = false;
       }
+
     } else if (ClassTemplateDecl *ClassTemplate1 =
                    dyn_cast<ClassTemplateDecl>(D1)) {
       if (ClassTemplateDecl *ClassTemplate2 = dyn_cast<ClassTemplateDecl>(D2)) {
-        if (!::IsStructurallyEquivalent(ClassTemplate1->getIdentifier(),
-                                        ClassTemplate2->getIdentifier()) ||
-            !::IsStructurallyEquivalent(*this, ClassTemplate1, ClassTemplate2))
+        if (!::IsStructurallyEquivalent(*this, ClassTemplate1,
+                                        ClassTemplate2))
           Equivalent = false;
       } else {
         // Class template/non-class-template mismatch.
         Equivalent = false;
       }
+
+    } else if (FunctionTemplateDecl *FunctionTemplate1 =
+               dyn_cast<FunctionTemplateDecl>(D1)) {
+      if (FunctionTemplateDecl *FunctionTemplate2 =
+          dyn_cast<FunctionTemplateDecl>(D2)) {
+        if (!::IsStructurallyEquivalent(*this, FunctionTemplate1,
+                                        FunctionTemplate2))
+          Equivalent = false;
+      } else {
+        // Class template/non-class-template mismatch.
+        Equivalent = false;
+      }
+
     } else if (TemplateTypeParmDecl *TTP1 =
                    dyn_cast<TemplateTypeParmDecl>(D1)) {
       if (TemplateTypeParmDecl *TTP2 = dyn_cast<TemplateTypeParmDecl>(D2)) {
@@ -1350,6 +1387,7 @@ bool StructuralEquivalenceContext::Finish() {
         // Kind mismatch.
         Equivalent = false;
       }
+
     } else if (TemplateTemplateParmDecl *TTP1 =
                    dyn_cast<TemplateTemplateParmDecl>(D1)) {
       if (TemplateTemplateParmDecl *TTP2 =
diff --git a/clang/lib/AST/ExternalASTMerger.cpp b/clang/lib/AST/ExternalASTMerger.cpp
index 6b75c51c642..91de8dbca05 100644
--- a/clang/lib/AST/ExternalASTMerger.cpp
+++ b/clang/lib/AST/ExternalASTMerger.cpp
@@ -16,6 +16,7 @@
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclObjC.h"
+#include "clang/AST/DeclTemplate.h"
 #include "clang/AST/ExternalASTMerger.h"
 
 using namespace clang;
@@ -351,6 +352,27 @@ void ExternalASTMerger::RemoveSources(llvm::ArrayRef<ImporterSource> Sources) {
   }
 }
 
+template <typename DeclTy>
+static bool importSpecializations(DeclTy *D, ASTImporter *Importer) {
+  for (auto *Spec : D->specializations())
+    if (!Importer->Import(Spec))
+      return true;
+  return false;
+}
+
+/// Imports specializations from template declarations that can be specialized.
+static bool importSpecializationsIfNeeded(Decl *D, ASTImporter *Importer) {
+  if (!isa<TemplateDecl>(D))
+    return false;
+  if (auto *FunctionTD = dyn_cast<FunctionTemplateDecl>(D))
+    return importSpecializations(FunctionTD, Importer);
+  else if (auto *ClassTD = dyn_cast<ClassTemplateDecl>(D))
+    return importSpecializations(ClassTD, Importer);
+  else if (auto *VarTD = dyn_cast<VarTemplateDecl>(D))
+    return importSpecializations(VarTD, Importer);
+  return false;
+}
+
 bool ExternalASTMerger::FindExternalVisibleDeclsByName(const DeclContext *DC,
                                                        DeclarationName Name) {
   llvm::SmallVector<NamedDecl *, 1> Decls;
@@ -376,9 +398,17 @@ bool ExternalASTMerger::FindExternalVisibleDeclsByName(const DeclContext *DC,
 
   Decls.reserve(Candidates.size());
   for (const Candidate &C : Candidates) {
-    NamedDecl *d = cast<NamedDecl>(C.second->Import(C.first.get()));
-    assert(d);
-    Decls.push_back(d);
+    Decl *LookupRes = C.first.get();
+    ASTImporter *Importer = C.second;
+    NamedDecl *ND = cast_or_null<NamedDecl>(Importer->Import(LookupRes));
+    assert(ND);
+    // If we don't import specialization, they are not available via lookup
+    // because the lookup result is imported TemplateDecl and it does not
+    // reference its specializations until they are imported explicitly.
+    bool IsSpecImportFailed =
+        importSpecializationsIfNeeded(LookupRes, Importer);
+    assert(!IsSpecImportFailed);
+    Decls.push_back(ND);
   }
   SetExternalVisibleDeclsForName(DC, Name, Decls);
   return true;