[ASTImporter] Fix redecl chain of classes and class templates

[martong]

Summary

The crux of the issue that is being fixed is that lookup could not find
previous decls of a friend class. The solution involves making the
friend declarations visible in their decl context (i.e. adding them to
the lookup table).
Also, we simplify VisitRecordDecl greatly.

This fix involves two other repairs (without these the unittests fail):
(1) We could not handle the addition of injected class types properly
when a redecl chain was involved, now this is fixed.
(2) DeclContext::removeDecl failed if the lookup table in Vector form
did not contain the to be removed element. This caused troubles in
ASTImporter::ImportDeclContext. This is also fixed.

[Szelethus]

I can't add anything meaningful to the conversation, but I spotted some nits, so here they are.

include/clang/ASTMatchers/ASTMatchers.h

1167

Did you mean to write indirectFieldDecl()?

lib/AST/ASTImporter.cpp

2672

Hah. We should do this more often.

lib/AST/DeclBase.cpp

1469–1471

Contained in?

[balazske]

lib/AST/ASTImporter.cpp

5064

This is a long line that should be split.

[martong]

• Minor style changes and rename a function

[martong]

lib/AST/DeclBase.cpp

1469–1471

Indeed, containedInVector sounds better, so I renamed.

[balazske]

lib/AST/DeclBase.cpp

1469–1471

For me, containsInVector is the better name, or hasInVector ("contains" is already used at other places but not "contained" and it sounds like it is not contained any more).

[Szelethus]

lib/AST/DeclBase.cpp

1469–1471

Sorry about the confusion, my inline was only about the comment above it, that it isn't obvious enough that what decl is contained in. But after taking a second look, it's very clear that only Map is mutated in this context, so I don't insist on any modification :)

[martong]

• Revert "Minor style changes and rename a function"

[martong]

lib/AST/DeclBase.cpp

1469–1471

Okay, so I just reverted the name change.

[balazske]

I see that now everything is reverted, the "good" things too (change to indirectFieldDecl and a line split)?

[martong]

• Keep the good changes and use the name 'containsInVector'

[martong]

I see that now everything is reverted, the "good" things too (change to indirectFieldDecl and a line split)?

Yes, you are completely right, sorry for this mess. I just have updated so the good things remain.

[balazske]

Do not forget that there is a fix the to use getMostRecentDecl in ASTImporter.cpp line 2666 here.

[martong]

• Use MostRecentDecl when setting PrevDecl

[martong]

This will break LLDB, unless https://reviews.llvm.org/D54863 is applied. @shafik Could you please take a look on https://reviews.llvm.org/D54863 ?

[a_sidorin]

Hi Gabor,

The change looks mostly Ok but there are some comments inline.

include/clang/AST/DeclContextInternals.h

128

auto I = llvm::find(Vec, D)?

lib/AST/ASTImporter.cpp

2638

because (typo)

2649–2651

IsStructuralMatch check will be repeated if (!SearchName && IsStructuralMatch). Is it expected behaviour?

2672

Unfortunately, it is a clear sign that we have to simplify the function. It's better to leave a FIXME instead.

2826

Are these lines removed due to move of MapImported into Create helper?

5001–5003

Space after '*'?

unittests/AST/ASTImporterTest.cpp

3794

Will DeclsFromFriendsShouldBeInRedeclChains without number appear in another patch?

[a_sidorin]

Please note that changes in AST lib will require AST code owners' approval. @rsmith, @aaron.ballman could you please take a look?

[aaron.ballman]

include/clang/AST/DeclContextInternals.h

125

const NamedDecl *D

126

Please add a string literal to the assert explaining what is being checked here.

128

I'd go with return llvm::is_contained(Vec, D);

include/clang/ASTMatchers/ASTMatchers.h

1169

Be sure to update Registry.cpp and regenerate the AST matcher documentation by running clang\docs\tools\dump_ast_matchers.py.

This change feels orthogonal to the rest of the patch; perhaps it should be split out into its own patch?

lib/AST/ASTImporter.cpp

2729

Drop the top-level const qualifier.

2730

Elide braces; I'd probably sink the IsFriend into here since it's not used elsewhere.

5001–5003

Space before the asterisk. ;-)

5064

Do not use auto here as the type is not spelled out in the initialization.

5073

Elide braces.

[martong]

include/clang/ASTMatchers/ASTMatchers.h

1169

This change feels orthogonal to the rest of the patch; perhaps it should be split out into its own patch?

I agree this part could go into a separate patch, but the first use of this new ASTMatcher is in the new unittests of this patch, so I think it fits better to add them here.

lib/AST/ASTImporter.cpp

2649–2651

Yes, this is intentional.
The first check does not emit any diagnostics. However, in the case you mention (if (!SearchName && IsStructuralMatch)) we have to emit diagnostics, because we found a real mismatch.

2672

I agree. Further, we should simplify all Visit*Decl functions where we iterate over the lookup results. The whole iteration could be part of a subroutine with a name like FindEquivalentPreviousDecl. But, I'd do that as a separate patch which focuses only on that refactor.

5064

Good catch.

unittests/AST/ASTImporterTest.cpp

3794

Sorry, 2 is an obsolete postfix. Removed it.

[martong]

• Address several minor review comments

[aaron.ballman]

This seems mostly reasonable to me, but @rsmith is more well-versed in this area and may have further comments. You should give him a few days to chime in before committing.

include/clang/AST/DeclContextInternals.h

125–129

Given that this is only called in one place and is effectively a one-liner, I'd get rid of this function entirely and replace the call below.

include/clang/ASTMatchers/ASTMatchers.h

1169

Okay, that's fair enough.

[martong]

include/clang/AST/DeclContextInternals.h

125–129

Good catch, thank you.

lib/AST/ASTImporter.cpp

2826

Yes, exactly.

[martong]

• Remove containsInVector

[martong]

@aaron.ballman Thanks for your review. I have updated the patch to remove containsInVector.

This seems mostly reasonable to me, but @rsmith is more well-versed in this area and may have further comments. You should give him a few days to chime in before committing.

Of course.

[martong]

@rsmith ping

[martong]

@rsmith Please raise any objections until Dec 14 (or if this deadline is too strict). I'd like to commit this next week latest so it can get in still this year.

include/clang/AST/DeclContextInternals.h

void remove(NamedDecl *D) {
     DeclsTy::iterator I = std::find(Vec.begin(), Vec.end(), D);
     assert(I != Vec.end() && "list does not contain decl");
     Vec.erase(I);
 
     assert(std::find(Vec.begin(), Vec.end(), D)
              == Vec.end() && "list still contains decl");
   }
 
+  bool containedInVector(NamedDecl *D) {
+    assert(getAsVector());
+    DeclsTy &Vec = *getAsVector();
+    DeclsTy::iterator I = std::find(Vec.begin(), Vec.end(), D);
+    return I != Vec.end();
+  }
+
   /// Remove any declarations which were imported from an external
   /// AST source.
   void removeExternalDecls() {
     if (isNull()) {
       // Nothing to do.
     } else if (NamedDecl *Singleton = getAsDecl()) {
       if (Singleton->isFromASTFile())
         *this = StoredDeclsList();

include/clang/ASTMatchers/ASTMatchers.h

 /// Given
 /// \code
 ///   class X { int m; };
 /// \endcode
 /// fieldDecl()
 ///   matches 'm'.
 extern const internal::VariadicDynCastAllOfMatcher<Decl, FieldDecl> fieldDecl;
 
+/// Matches indirect field declarations.
+///
+/// Given
+/// \code
+///   struct X { struct { int a; }; };
+/// \endcode
+/// indirectFieldDecl()
+///   matches 'a'.
+extern const internal::VariadicDynCastAllOfMatcher<Decl, IndirectFieldDecl>
+    indirectFieldDecl;
+
 /// Matches function declarations.
 ///
 /// Example matches f
 /// \code
 ///   void f();
 /// \endcode
 extern const internal::VariadicDynCastAllOfMatcher<Decl, FunctionDecl>
     functionDecl;

lib/AST/ASTImporter.cpp

getCanonicalForwardRedeclChain(Redeclarable<T>* D) {
     return Redecls;
   }
 
   SmallVector<Decl*, 2> getCanonicalForwardRedeclChain(Decl* D) {
     if (auto *FD = dyn_cast<FunctionDecl>(D))
       return getCanonicalForwardRedeclChain<FunctionDecl>(FD);
     if (auto *VD = dyn_cast<VarDecl>(D))
       return getCanonicalForwardRedeclChain<VarDecl>(VD);
+    if (auto *TD = dyn_cast<TagDecl>(D))
+      return getCanonicalForwardRedeclChain<TagDecl>(TD);
     llvm_unreachable("Bad declaration kind");
   }
 
   void updateFlags(const Decl *From, Decl *To) {
     // Check if some flags or attrs are new in 'From' and copy into 'To'.
     // FIXME: Other flags or attrs?
     if (From->isUsed(false) && !To->isUsed(false))
       To->setIsUsed();
ExpectedDecl ASTNodeImporter::VisitRecordDecl(RecordDecl *D) {
   unsigned IDNS = Decl::IDNS_Tag;
   DeclarationName SearchName = Name;
   if (!SearchName && D->getTypedefNameForAnonDecl()) {
     if (Error Err = importInto(
         SearchName, D->getTypedefNameForAnonDecl()->getDeclName()))
       return std::move(Err);
     IDNS = Decl::IDNS_Ordinary;
   } else if (Importer.getToContext().getLangOpts().CPlusPlus)
-    IDNS |= Decl::IDNS_Ordinary;
+    IDNS |= Decl::IDNS_Ordinary | Decl::IDNS_TagFriend;
 
   // We may already have a record of the same name; try to find and match it.
-  RecordDecl *AdoptDecl = nullptr;
   RecordDecl *PrevDecl = nullptr;
   if (!DC->isFunctionOrMethod()) {
     SmallVector<NamedDecl *, 4> ConflictingDecls;
     SmallVector<NamedDecl *, 2> FoundDecls;
     DC->getRedeclContext()->localUncachedLookup(SearchName, FoundDecls);
 
     if (!FoundDecls.empty()) {
       // We're going to have to compare D against potentially conflicting Decls, so complete it.
for (auto *FoundDecl : FoundDecls) {
           Found = Template->getTemplatedDecl();
         } else {
           ConflictingDecls.push_back(FoundDecl);
           continue;
         }
       }
 
       if (auto *FoundRecord = dyn_cast<RecordDecl>(Found)) {
-        if (!SearchName) {
+        // Do not emit false positive diagnostic in case of unnamed
+        // struct/union and in case of anonymous structs.  Would be false
+        // becasue there may be several anonymous/unnamed structs in a class.
+        // E.g. these are both valid:
+        //  struct A { // unnamed structs
+        //    struct { struct A *next; } entry0;
+        //    struct { struct A *next; } entry1;
+        //  };
+        //  struct X { struct { int a; }; struct { int b; }; }; // anon structs
+        if (!SearchName)
           if (!IsStructuralMatch(D, FoundRecord, false))
             continue;
-        } else {
-          if (!IsStructuralMatch(D, FoundRecord)) {
-            ConflictingDecls.push_back(FoundDecl);
-            continue;
-          }
-        }
-
-        PrevDecl = FoundRecord;
 
-        if (RecordDecl *FoundDef = FoundRecord->getDefinition()) {
-          if ((SearchName && !D->isCompleteDefinition() && !IsFriendTemplate)
-              || (D->isCompleteDefinition() &&
-                  D->isAnonymousStructOrUnion()
-                    == FoundDef->isAnonymousStructOrUnion())) {
-            // The record types structurally match, or the "from" translation
-            // unit only had a forward declaration anyway; call it the same
-            // function.
+        if (IsStructuralMatch(D, FoundRecord)) {
+          RecordDecl *FoundDef = FoundRecord->getDefinition();
+          if (D->isThisDeclarationADefinition() && FoundDef) {
             // FIXME: Structural equivalence check should check for same
             // user-defined methods.
             Importer.MapImported(D, FoundDef);
             if (const auto *DCXX = dyn_cast<CXXRecordDecl>(D)) {
               auto *FoundCXX = dyn_cast<CXXRecordDecl>(FoundDef);
               assert(FoundCXX && "Record type mismatch");
 
-              if (D->isCompleteDefinition() && !Importer.isMinimalImport())
+              if (!Importer.isMinimalImport())
                 // FoundDef may not have every implicit method that D has
                 // because implicit methods are created only if they are used.
                 if (Error Err = ImportImplicitMethods(DCXX, FoundCXX))
                   return std::move(Err);
             }
-            return FoundDef;
           }
-          if (IsFriendTemplate)
-            continue;
-        } else if (!D->isCompleteDefinition()) {
-          // We have a forward declaration of this type, so adopt that forward
-          // declaration rather than building a new one.
-
-          // If one or both can be completed from external storage then try one
-          // last time to complete and compare them before doing this.
-
-          if (FoundRecord->hasExternalLexicalStorage() &&
-              !FoundRecord->isCompleteDefinition())
-            FoundRecord->getASTContext().getExternalSource()->CompleteType(FoundRecord);
-          if (D->hasExternalLexicalStorage())
-            D->getASTContext().getExternalSource()->CompleteType(D);
-
-          if (FoundRecord->isCompleteDefinition() &&
-              D->isCompleteDefinition() &&
-              !IsStructuralMatch(D, FoundRecord)) {
-            ConflictingDecls.push_back(FoundDecl);
-            continue;
-          }
-
-          AdoptDecl = FoundRecord;
-          continue;
-        }
+          PrevDecl = FoundRecord;
+          break;
 
-        continue;
-      } else if (isa<ValueDecl>(Found))
-        continue;
-
       ConflictingDecls.push_back(FoundDecl);
-    }
+    } // for
 
     if (!ConflictingDecls.empty() && SearchName) {
       Name = Importer.HandleNameConflict(Name, DC, IDNS,
                                          ConflictingDecls.data(),
                                          ConflictingDecls.size());
       if (!Name)
         return make_error<ImportError>(ImportError::NameConflict);
     }
   }
 
   ExpectedSLoc BeginLocOrErr = import(D->getBeginLoc());
   if (!BeginLocOrErr)
     return BeginLocOrErr.takeError();
 
   // Create the record declaration.
-  RecordDecl *D2 = AdoptDecl;
-  if (!D2) {
-    CXXRecordDecl *D2CXX = nullptr;
-    if (auto *DCXX = dyn_cast<CXXRecordDecl>(D)) {
-      if (DCXX->isLambda()) {
-        auto TInfoOrErr = import(DCXX->getLambdaTypeInfo());
-        if (!TInfoOrErr)
-          return TInfoOrErr.takeError();
-        if (GetImportedOrCreateSpecialDecl(
-                D2CXX, CXXRecordDecl::CreateLambda, D, Importer.getToContext(),
-                DC, *TInfoOrErr, Loc, DCXX->isDependentLambda(),
-                DCXX->isGenericLambda(), DCXX->getLambdaCaptureDefault()))
-          return D2CXX;
-        ExpectedDecl CDeclOrErr = import(DCXX->getLambdaContextDecl());
-        if (!CDeclOrErr)
-          return CDeclOrErr.takeError();
-        D2CXX->setLambdaMangling(DCXX->getLambdaManglingNumber(), *CDeclOrErr);
-      } 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;
-        if (GetImportedOrCreateDecl(D2CXX, D, Importer.getToContext(),
-                                    D->getTagKind(), DC, *BeginLocOrErr, Loc,
-                                    Name.getAsIdentifierInfo(), PrevDecl,
-                                    DelayTypeCreation))
-          return D2CXX;
-        Importer.getToContext().getTypeDeclType(
-            D2CXX, dyn_cast<CXXRecordDecl>(DC));
-      } else {
-        if (GetImportedOrCreateDecl(D2CXX, D, Importer.getToContext(),
-                                    D->getTagKind(), DC, *BeginLocOrErr, Loc,
-                                    Name.getAsIdentifierInfo(),
-                                    cast_or_null<CXXRecordDecl>(PrevDecl)))
-          return D2CXX;
-      }
+  RecordDecl *D2 = nullptr;
+      if (GetImportedOrCreateDecl(
+              D2CXX, D, Importer.getToContext(), D->getTagKind(), DC,
+              *BeginLocOrErr, Loc, Name.getAsIdentifierInfo(),
+              cast_or_null<CXXRecordDecl>(PrevDecl), DelayTypeCreation))
 
-      D2 = D2CXX;
-      D2->setAccess(D->getAccess());
-      D2->setLexicalDeclContext(LexicalDC);
-      if (!DCXX->getDescribedClassTemplate() || DCXX->isImplicit())
-        LexicalDC->addDeclInternal(D2);
 
-      if (ClassTemplateDecl *FromDescribed =
-          DCXX->getDescribedClassTemplate()) {
-        ClassTemplateDecl *ToDescribed;
-        if (Error Err = importInto(ToDescribed, FromDescribed))
-          return std::move(Err);
-        D2CXX->setDescribedClassTemplate(ToDescribed);
-        if (!DCXX->isInjectedClassName() && !IsFriendTemplate) {
-          // In a record describing a template the type should be an
-          // InjectedClassNameType (see Sema::CheckClassTemplate). Update the
-          // previously set type to the correct value here (ToDescribed is not
-          // available at record create).
-          // FIXME: The previous type is cleared but not removed from
-          // ASTContext's internal storage.
-          CXXRecordDecl *Injected = nullptr;
-          for (NamedDecl *Found : D2CXX->noload_lookup(Name)) {
-            auto *Record = dyn_cast<CXXRecordDecl>(Found);
-            if (Record && Record->isInjectedClassName()) {
-              Injected = Record;
-              break;
-            }
-          }
-          D2CXX->setTypeForDecl(nullptr);
-          Importer.getToContext().getInjectedClassNameType(D2CXX,
-              ToDescribed->getInjectedClassNameSpecialization());
-          if (Injected) {
-            Injected->setTypeForDecl(nullptr);
-            Importer.getToContext().getTypeDeclType(Injected, D2CXX);
-          }
-        }
-      } else if (MemberSpecializationInfo *MemberInfo =
+    const bool IsFriend = D->isInIdentifierNamespace(Decl::IDNS_TagFriend);
+    if (LexicalDC != DC && IsFriend) {
+      DC->makeDeclVisibleInContext(D2);
+    }
+
+        // Create an injected type for the whole redecl chain.
+        SmallVector<Decl *, 2> Redecls =
+            getCanonicalForwardRedeclChain(D2CXX);
+        for (auto *R : Redecls) {
+          auto *RI = cast<CXXRecordDecl>(R);
+          RI->setTypeForDecl(nullptr);
+          // Below we create a new injected type and assign that to the
+          // canonical decl, subsequent declarations in the chain will reuse
+          // that type.
+          Importer.getToContext().getInjectedClassNameType(
+              RI, ToDescribed->getInjectedClassNameSpecialization());
+        }
+        // Set the new type for the previous injected decl too.
                    DCXX->getMemberSpecializationInfo()) {
         TemplateSpecializationKind SK =
             MemberInfo->getTemplateSpecializationKind();
         CXXRecordDecl *FromInst = DCXX->getInstantiatedFromMemberClass();
 
         if (Expected<CXXRecordDecl *> ToInstOrErr = import(FromInst))
           D2CXX->setInstantiationOfMemberClass(*ToInstOrErr, SK);
         else
           return ToInstOrErr.takeError();
 
         if (ExpectedSLoc POIOrErr =
             import(MemberInfo->getPointOfInstantiation()))
           D2CXX->getMemberSpecializationInfo()->setPointOfInstantiation(
             *POIOrErr);
         else
           return POIOrErr.takeError();
-      }
 
-    } else {
-      if (GetImportedOrCreateDecl(D2, D, Importer.getToContext(),
-                                  D->getTagKind(), DC, *BeginLocOrErr, Loc,
-                                  Name.getAsIdentifierInfo(), PrevDecl))
-        return D2;
-      D2->setLexicalDeclContext(LexicalDC);
-      LexicalDC->addDeclInternal(D2);
-    }
 
-    if (auto QualifierLocOrErr = import(D->getQualifierLoc()))
-      D2->setQualifierInfo(*QualifierLocOrErr);
-    else
-      return QualifierLocOrErr.takeError();
 
-    if (D->isAnonymousStructOrUnion())
-      D2->setAnonymousStructOrUnion(true);
-  }
-
-  Importer.MapImported(D, D2);
 
   if (D->isCompleteDefinition())
     if (Error Err = ImportDefinition(D, D2, IDK_Default))
       return std::move(Err);
 
   return D2;
 }
 
static ClassTemplateDecl *getDefinition(ClassTemplateDecl *D) {
   ClassTemplateDecl *TemplateWithDef =
       ToTemplatedDef->getDescribedClassTemplate();
   return TemplateWithDef;
 }
 
 ExpectedDecl ASTNodeImporter::VisitClassTemplateDecl(ClassTemplateDecl *D) {
   bool IsFriend = D->getFriendObjectKind() != Decl::FOK_None;
 
-  // If this record has a definition in the translation unit we're coming from,
-  // but this particular declaration is not that definition, import the
+  // If this template has a definition in the translation unit we're coming
+  // from, but this particular declaration is not that definition, import the
   // definition and map to that.
-  auto *Definition =
-      cast_or_null<CXXRecordDecl>(D->getTemplatedDecl()->getDefinition());
-  if (Definition && Definition != D->getTemplatedDecl() && !IsFriend) {
-    if (ExpectedDecl ImportedDefOrErr = import(
-        Definition->getDescribedClassTemplate()))
+  ClassTemplateDecl *Definition = getDefinition(D);
+  if (Definition && Definition != D && !IsFriend) {
+    if (ExpectedDecl ImportedDefOrErr = import(Definition))
       return Importer.MapImported(D, *ImportedDefOrErr);
     else
       return ImportedDefOrErr.takeError();
   }
 
   // Import the major distinguishing characteristics of this class template.
   DeclContext *DC, *LexicalDC;
   DeclarationName Name;
   SourceLocation Loc;
   NamedDecl *ToD;
   if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
     return std::move(Err);
   if (ToD)
     return ToD;
 
+  ClassTemplateDecl *FoundByLookup = nullptr;
+
   // We may already have a template of the same name; try to find and match it.
   if (!DC->isFunctionOrMethod()) {
     SmallVector<NamedDecl *, 4> ConflictingDecls;
     SmallVector<NamedDecl *, 2> FoundDecls;
     DC->getRedeclContext()->localUncachedLookup(Name, FoundDecls);
     for (auto *FoundDecl : FoundDecls) {
-      if (!FoundDecl->isInIdentifierNamespace(Decl::IDNS_Ordinary))
+      if (!FoundDecl->isInIdentifierNamespace(Decl::IDNS_Ordinary |
+                                              Decl::IDNS_TagFriend))
         continue;
 
       Decl *Found = FoundDecl;
-      if (auto *FoundTemplate = dyn_cast<ClassTemplateDecl>(Found)) {
-
-        // The class to be imported is a definition.
-        if (D->isThisDeclarationADefinition()) {
-          // Lookup will find the fwd decl only if that is more recent than the
-          // definition. So, try to get the definition if that is available in
-          // the redecl chain.
-          ClassTemplateDecl *TemplateWithDef = getDefinition(FoundTemplate);
-          if (TemplateWithDef)
-            FoundTemplate = TemplateWithDef;
-          else
-            continue;
-        }
+      auto *FoundTemplate = dyn_cast<ClassTemplateDecl>(Found);
+      if (FoundTemplate) {
 
         if (IsStructuralMatch(D, FoundTemplate)) {
-          if (!IsFriend) {
-            Importer.MapImported(D->getTemplatedDecl(),
-                                 FoundTemplate->getTemplatedDecl());
-            return Importer.MapImported(D, FoundTemplate);
+          ClassTemplateDecl* TemplateWithDef = getDefinition(FoundTemplate);
+          if (D->isThisDeclarationADefinition() && TemplateWithDef) {
+            return Importer.MapImported(D, TemplateWithDef);
           }
-
-          continue;
+          FoundByLookup = FoundTemplate;
+          break;
         }
       }
 
       ConflictingDecls.push_back(FoundDecl);
     }
 
     if (!ConflictingDecls.empty()) {
       Name = Importer.HandleNameConflict(Name, DC, Decl::IDNS_Ordinary,
ExpectedDecl ASTNodeImporter::VisitClassTemplateDecl(ClassTemplateDecl *D) {
 
   ClassTemplateDecl *D2;
   if (GetImportedOrCreateDecl(D2, D, Importer.getToContext(), DC, Loc, Name,
                               *TemplateParamsOrErr, ToTemplated))
     return D2;
 
   ToTemplated->setDescribedClassTemplate(D2);
 
-  if (ToTemplated->getPreviousDecl()) {
-    assert(
-        ToTemplated->getPreviousDecl()->getDescribedClassTemplate() &&
-        "Missing described template");
-    D2->setPreviousDecl(
-        ToTemplated->getPreviousDecl()->getDescribedClassTemplate());
-  }
   D2->setAccess(D->getAccess());
   D2->setLexicalDeclContext(LexicalDC);
-  if (!IsFriend)
+
+  if (D->getDeclContext()->containsDeclAndLoad(D))
+    DC->addDeclInternal(D2);
+  if (DC != LexicalDC && D->getLexicalDeclContext()->containsDeclAndLoad(D))
     LexicalDC->addDeclInternal(D2);
 
+  if (FoundByLookup) {
+    auto *Recent =
+        const_cast<ClassTemplateDecl *>(FoundByLookup->getMostRecentDecl());
+
+    // It is possible that during the import of the class template definition
+    // we start the import of a fwd friend decl of the very same class template
+    // and we add the fwd friend decl to the lookup table. But the ToTemplated
+    // had been created earlier and by that time the lookup could not find
+    // anything existing, so it has no previous decl. Later, (still during the
+    // import of the fwd friend decl) we start to import the definition again
+    // and this time the lookup finds the previous fwd friend class template.
+    // In this case we must set up the previous decl for the templated decl.
+    if (!ToTemplated->getPreviousDecl()) {
+      auto *PrevTemplated =
+          FoundByLookup->getTemplatedDecl()->getMostRecentDecl();
+      if (ToTemplated != PrevTemplated)
+        ToTemplated->setPreviousDecl(PrevTemplated);
+    }
+
+    D2->setPreviousDecl(Recent);
+  }
+
+  if (LexicalDC != DC && IsFriend) {
+    DC->makeDeclVisibleInContext(D2);
+  }
+
   if (FromTemplated->isCompleteDefinition() &&
       !ToTemplated->isCompleteDefinition()) {
     // FIXME: Import definition!
   }
 
   return D2;
 }
 

lib/AST/DeclBase.cpp

if (!ND->getDeclName())
       return;
 
     auto *DC = D->getDeclContext();
     do {
       StoredDeclsMap *Map = DC->getPrimaryContext()->LookupPtr;
       if (Map) {
         StoredDeclsMap::iterator Pos = Map->find(ND->getDeclName());
         assert(Pos != Map->end() && "no lookup entry for decl");
-        if (Pos->second.getAsVector() || Pos->second.getAsDecl() == ND)
+        // Remove the decl only if it is contained.
+        if ((Pos->second.getAsVector() && Pos->second.containedInVector(ND)) ||
+            Pos->second.getAsDecl() == ND)
           Pos->second.remove(ND);
       }
     } while (DC->isTransparentContext() && (DC = DC->getParent()));
   }
 }
 
 void DeclContext::addHiddenDecl(Decl *D) {
   assert(D->getLexicalDeclContext() == this &&

lib/ASTMatchers/ASTMatchersInternal.cpp

 const internal::VariadicDynCastAllOfMatcher<Decl, EnumDecl> enumDecl;
 const internal::VariadicDynCastAllOfMatcher<Decl, EnumConstantDecl>
     enumConstantDecl;
 const internal::VariadicDynCastAllOfMatcher<Decl, CXXMethodDecl> cxxMethodDecl;
 const internal::VariadicDynCastAllOfMatcher<Decl, CXXConversionDecl>
     cxxConversionDecl;
 const internal::VariadicDynCastAllOfMatcher<Decl, VarDecl> varDecl;
 const internal::VariadicDynCastAllOfMatcher<Decl, FieldDecl> fieldDecl;
+const internal::VariadicDynCastAllOfMatcher<Decl, IndirectFieldDecl>
+    indirectFieldDecl;
 const internal::VariadicDynCastAllOfMatcher<Decl, FunctionDecl> functionDecl;
 const internal::VariadicDynCastAllOfMatcher<Decl, FunctionTemplateDecl>
     functionTemplateDecl;
 const internal::VariadicDynCastAllOfMatcher<Decl, FriendDecl> friendDecl;
 const internal::VariadicAllOfMatcher<Stmt> stmt;
 const internal::VariadicDynCastAllOfMatcher<Stmt, DeclStmt> declStmt;
 const internal::VariadicDynCastAllOfMatcher<Stmt, MemberExpr> memberExpr;
 const internal::VariadicDynCastAllOfMatcher<Stmt, UnresolvedMemberExpr>

unittests/AST/ASTImporterTest.cpp

 //===- unittest/AST/ASTImporterTest.cpp - AST node import test ------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // Tests for the correct import of AST nodes from one AST context to another.
 //
 //===----------------------------------------------------------------------===//
 
+#include "clang/AST/ASTImporter.h"
 #include "MatchVerifier.h"
 #include "clang/AST/ASTContext.h"
-#include "clang/AST/ASTImporter.h"
+#include "clang/AST/DeclContextInternals.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/ASTMatchers/ASTMatchers.h"
 #include "clang/Tooling/Tooling.h"
 
 #include "DeclMatcher.h"
 #include "Language.h"
 #include "gmock/gmock.h"
 #include "llvm/ADT/StringMap.h"
TEST_P(ASTImporterTestBase, ObjectsWithUnnamedStructType) {
   auto *To1 = Import(From1, Lang_CXX);
 
   EXPECT_TRUE(To0);
   EXPECT_TRUE(To1);
   EXPECT_NE(To0, To1);
   EXPECT_NE(To0->getCanonicalDecl(), To1->getCanonicalDecl());
 }
 
+TEST_P(ASTImporterTestBase, AnonymousRecords) {
+  auto *Code =
+      R"(
+      struct X {
+        struct { int a; };
+        struct { int b; };
+      };
+      )";
+  Decl *FromTU0 = getTuDecl(Code, Lang_C, "input0.c");
+
+  Decl *FromTU1 = getTuDecl(Code, Lang_C, "input1.c");
+
+  auto *X0 =
+      FirstDeclMatcher<RecordDecl>().match(FromTU0, recordDecl(hasName("X")));
+  auto *X1 =
+      FirstDeclMatcher<RecordDecl>().match(FromTU1, recordDecl(hasName("X")));
+  Import(X0, Lang_C);
+  Import(X1, Lang_C);
+
+  auto *ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  // We expect no (ODR) warning during the import.
+  EXPECT_EQ(0u, ToTU->getASTContext().getDiagnostics().getNumWarnings());
+  EXPECT_EQ(1u,
+            DeclCounter<RecordDecl>().match(ToTU, recordDecl(hasName("X"))));
+}
+
+TEST_P(ASTImporterTestBase, AnonymousRecordsReversed) {
+  Decl *FromTU0 = getTuDecl(
+      R"(
+      struct X {
+        struct { int a; };
+        struct { int b; };
+      };
+      )",
+      Lang_C, "input0.c");
+
+  Decl *FromTU1 = getTuDecl(
+      R"(
+      struct X { // reversed order
+        struct { int b; };
+        struct { int a; };
+      };
+      )",
+      Lang_C, "input1.c");
+
+  auto *X0 =
+      FirstDeclMatcher<RecordDecl>().match(FromTU0, recordDecl(hasName("X")));
+  auto *X1 =
+      FirstDeclMatcher<RecordDecl>().match(FromTU1, recordDecl(hasName("X")));
+  Import(X0, Lang_C);
+  Import(X1, Lang_C);
+
+  auto *ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  // We expect one (ODR) warning during the import.
+  EXPECT_EQ(1u, ToTU->getASTContext().getDiagnostics().getNumWarnings());
+  EXPECT_EQ(2u,
+            DeclCounter<RecordDecl>().match(ToTU, recordDecl(hasName("X"))));
+}
+
 TEST_P(ASTImporterTestBase, ImportDoesUpdateUsedFlag) {
   auto Pattern = varDecl(hasName("x"));
   VarDecl *Imported1;
   {
     Decl *FromTU = getTuDecl("extern int x;", Lang_CXX, "input0.cc");
     auto *FromD = FirstDeclMatcher<VarDecl>().match(FromTU, Pattern);
     Imported1 = cast<VarDecl>(Import(FromD, Lang_CXX));
   }
for (auto *FromField : FromLambda->fields()) {
     EXPECT_TRUE(ToIndex);
     EXPECT_EQ(*ToIndex, FromIndex);
     ++FromIndex;
   }
 
   EXPECT_EQ(FromIndex, 3u);
 }
 
-TEST_P(
-    ASTImporterTestBase,
-    ImportOfFriendRecordDoesNotMergeDefinition) {
-  Decl *FromTU = getTuDecl(
-      R"(
-      class A {
-        template <int I> class F {};
-        class X {
-          template <int I> friend class F;
-        };
-      };
-      )",
-      Lang_CXX, "input0.cc");
-
-  auto *FromClass = FirstDeclMatcher<CXXRecordDecl>().match(
-      FromTU, cxxRecordDecl(hasName("F"), isDefinition()));
-  auto *FromFriendClass = LastDeclMatcher<CXXRecordDecl>().match(
-      FromTU, cxxRecordDecl(hasName("F")));
-
-  ASSERT_TRUE(FromClass);
-  ASSERT_TRUE(FromFriendClass);
-  ASSERT_NE(FromClass, FromFriendClass);
-  ASSERT_EQ(FromFriendClass->getDefinition(), FromClass);
-  ASSERT_EQ(FromFriendClass->getPreviousDecl(), FromClass);
-  ASSERT_EQ(
-      FromFriendClass->getDescribedClassTemplate()->getPreviousDecl(),
-      FromClass->getDescribedClassTemplate());
-
-  auto *ToClass = cast<CXXRecordDecl>(Import(FromClass, Lang_CXX));
-  auto *ToFriendClass = cast<CXXRecordDecl>(Import(FromFriendClass, Lang_CXX));
-
-  EXPECT_TRUE(ToClass);
-  EXPECT_TRUE(ToFriendClass);
-  EXPECT_NE(ToClass, ToFriendClass);
-  EXPECT_EQ(ToFriendClass->getDefinition(), ToClass);
-  EXPECT_EQ(ToFriendClass->getPreviousDecl(), ToClass);
-  EXPECT_EQ(
-      ToFriendClass->getDescribedClassTemplate()->getPreviousDecl(),
-      ToClass->getDescribedClassTemplate());
-}
-
-TEST_P(
-    ASTImporterTestBase,
-    ImportOfRecursiveFriendClass) {
-  Decl *FromTu = getTuDecl(
-      R"(
-      class declToImport {
-        friend class declToImport;
-      };
-      )",
-      Lang_CXX, "input.cc");
-
-  auto *FromD = FirstDeclMatcher<CXXRecordDecl>().match(
-      FromTu, cxxRecordDecl(hasName("declToImport")));
-  auto *ToD = Import(FromD, Lang_CXX);
-  auto Pattern = cxxRecordDecl(hasName("declToImport"), has(friendDecl()));
-  ASSERT_TRUE(MatchVerifier<Decl>{}.match(FromD, Pattern));
-  EXPECT_TRUE(MatchVerifier<Decl>{}.match(ToD, Pattern));
-}
-
-TEST_P(
-    ASTImporterTestBase,
-    ImportOfRecursiveFriendClassTemplate) {
-  Decl *FromTu = getTuDecl(
-      R"(
-      template <class A> class declToImport {
-        template <class A1> friend class declToImport;
-      };
-      )",
-      Lang_CXX, "input.cc");
-
-  auto *FromD = FirstDeclMatcher<ClassTemplateDecl>().match(
-      FromTu, classTemplateDecl(hasName("declToImport")));
-  auto *ToD = Import(FromD, Lang_CXX);
-
-  auto Pattern = classTemplateDecl(
-      has(cxxRecordDecl(has(friendDecl(has(classTemplateDecl()))))));
-  ASSERT_TRUE(MatchVerifier<Decl>{}.match(FromD, Pattern));
-  EXPECT_TRUE(MatchVerifier<Decl>{}.match(ToD, Pattern));
-
-  auto *Class =
-      FirstDeclMatcher<ClassTemplateDecl>().match(ToD, classTemplateDecl());
-  auto *Friend = FirstDeclMatcher<FriendDecl>().match(ToD, friendDecl());
-  EXPECT_NE(Friend->getFriendDecl(), Class);
-  EXPECT_EQ(Friend->getFriendDecl()->getPreviousDecl(), Class);
-}
-
 TEST_P(ASTImporterTestBase, MergeFieldDeclsOfClassTemplateSpecialization) {
   std::string ClassTemplate =
       R"(
       template <typename T>
       struct X {
           int a{0}; // FieldDecl with InitListExpr
           X(char) : a(3) {}     // (1)
           X(int) {}             // (2)
TEST_P(ImportVariables, InitAndDefinitionAreInTheFromContext) {
   ASSERT_FALSE(ToD->getInit());
   ASSERT_FALSE(ToD->getDefinition());
 
   auto *ImportedD = cast<VarDecl>(Import(FromDWithDef, Lang_CXX11));
   EXPECT_TRUE(ImportedD->getAnyInitializer());
   EXPECT_TRUE(ImportedD->getDefinition());
 }
 
+struct ImportClasses : ASTImporterTestBase {};
+
+TEST_P(ImportClasses,
+       PrototypeShouldBeImportedAsAPrototypeWhenThereIsNoDefinition) {
+  Decl *FromTU = getTuDecl("class X;", Lang_CXX);
+  auto Pattern = cxxRecordDecl(hasName("X"), unless(isImplicit()));
+  auto FromD = FirstDeclMatcher<CXXRecordDecl>().match(FromTU, Pattern);
+
+  Decl *ImportedD = Import(FromD, Lang_CXX);
+  Decl *ToTU = ImportedD->getTranslationUnitDecl();
+
+  EXPECT_EQ(DeclCounter<CXXRecordDecl>().match(ToTU, Pattern), 1u);
+  auto ToD = LastDeclMatcher<CXXRecordDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedD == ToD);
+  EXPECT_FALSE(ToD->isThisDeclarationADefinition());
+}
+
+TEST_P(ImportClasses, ImportPrototypeAfterImportedPrototype) {
+  Decl *FromTU = getTuDecl("class X; class X;", Lang_CXX);
+  auto Pattern = cxxRecordDecl(hasName("X"), unless(isImplicit()));
+  auto From0 = FirstDeclMatcher<CXXRecordDecl>().match(FromTU, Pattern);
+  auto From1 = LastDeclMatcher<CXXRecordDecl>().match(FromTU, Pattern);
+
+  Decl *Imported0 = Import(From0, Lang_CXX);
+  Decl *Imported1 = Import(From1, Lang_CXX);
+  Decl *ToTU = Imported0->getTranslationUnitDecl();
+
+  EXPECT_EQ(DeclCounter<CXXRecordDecl>().match(ToTU, Pattern), 2u);
+  auto To0 = FirstDeclMatcher<CXXRecordDecl>().match(ToTU, Pattern);
+  auto To1 = LastDeclMatcher<CXXRecordDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(Imported0 == To0);
+  EXPECT_TRUE(Imported1 == To1);
+  EXPECT_FALSE(To0->isThisDeclarationADefinition());
+  EXPECT_FALSE(To1->isThisDeclarationADefinition());
+  EXPECT_EQ(To1->getPreviousDecl(), To0);
+}
+
+TEST_P(ImportClasses, DefinitionShouldBeImportedAsADefinition) {
+  Decl *FromTU = getTuDecl("class X {};", Lang_CXX);
+  auto Pattern = cxxRecordDecl(hasName("X"), unless(isImplicit()));
+  auto *FromD = FirstDeclMatcher<CXXRecordDecl>().match(FromTU, Pattern);
+
+  Decl *ImportedD = Import(FromD, Lang_CXX);
+  Decl *ToTU = ImportedD->getTranslationUnitDecl();
+
+  EXPECT_EQ(DeclCounter<CXXRecordDecl>().match(ToTU, Pattern), 1u);
+  EXPECT_TRUE(cast<CXXRecordDecl>(ImportedD)->isThisDeclarationADefinition());
+}
+
+TEST_P(ImportClasses, ImportPrototypeFromDifferentTUAfterImportedPrototype) {
+  Decl *FromTU0 = getTuDecl("class X;", Lang_CXX, "input0.cc");
+  Decl *FromTU1 = getTuDecl("class X;", Lang_CXX, "input1.cc");
+  auto Pattern = cxxRecordDecl(hasName("X"), unless(isImplicit()));
+  auto From0 = FirstDeclMatcher<CXXRecordDecl>().match(FromTU0, Pattern);
+  auto From1 = FirstDeclMatcher<CXXRecordDecl>().match(FromTU1, Pattern);
+
+  Decl *Imported0 = Import(From0, Lang_CXX);
+  Decl *Imported1 = Import(From1, Lang_CXX);
+  Decl *ToTU = Imported0->getTranslationUnitDecl();
+
+  EXPECT_EQ(DeclCounter<CXXRecordDecl>().match(ToTU, Pattern), 2u);
+  auto To0 = FirstDeclMatcher<CXXRecordDecl>().match(ToTU, Pattern);
+  auto To1 = LastDeclMatcher<CXXRecordDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(Imported0 == To0);
+  EXPECT_TRUE(Imported1 == To1);
+  EXPECT_FALSE(To0->isThisDeclarationADefinition());
+  EXPECT_FALSE(To1->isThisDeclarationADefinition());
+  EXPECT_EQ(To1->getPreviousDecl(), To0);
+}
+
+TEST_P(ImportClasses, ImportDefinitions) {
+  Decl *FromTU0 = getTuDecl("class X {};", Lang_CXX, "input0.cc");
+  Decl *FromTU1 = getTuDecl("class X {};", Lang_CXX, "input1.cc");
+  auto Pattern = cxxRecordDecl(hasName("X"), unless(isImplicit()));
+  auto From0 = FirstDeclMatcher<CXXRecordDecl>().match(FromTU0, Pattern);
+  auto From1 = FirstDeclMatcher<CXXRecordDecl>().match(FromTU1, Pattern);
+
+  Decl *Imported0 = Import(From0, Lang_CXX);
+  Decl *Imported1 = Import(From1, Lang_CXX);
+  Decl *ToTU = Imported0->getTranslationUnitDecl();
+
+  EXPECT_EQ(Imported0, Imported1);
+  EXPECT_EQ(DeclCounter<CXXRecordDecl>().match(ToTU, Pattern), 1u);
+  auto To0 = FirstDeclMatcher<CXXRecordDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(Imported0 == To0);
+  EXPECT_TRUE(To0->isThisDeclarationADefinition());
+}
+
+TEST_P(ImportClasses, ImportDefinitionThenPrototype) {
+  Decl *FromTU0 = getTuDecl("class X {};", Lang_CXX, "input0.cc");
+  Decl *FromTU1 = getTuDecl("class X;", Lang_CXX, "input1.cc");
+  auto Pattern = cxxRecordDecl(hasName("X"), unless(isImplicit()));
+  auto FromDef = FirstDeclMatcher<CXXRecordDecl>().match(FromTU0, Pattern);
+  auto FromProto = FirstDeclMatcher<CXXRecordDecl>().match(FromTU1, Pattern);
+
+  Decl *ImportedDef = Import(FromDef, Lang_CXX);
+  Decl *ImportedProto = Import(FromProto, Lang_CXX);
+  Decl *ToTU = ImportedDef->getTranslationUnitDecl();
+
+  EXPECT_NE(ImportedDef, ImportedProto);
+  EXPECT_EQ(DeclCounter<CXXRecordDecl>().match(ToTU, Pattern), 2u);
+  auto ToDef = FirstDeclMatcher<CXXRecordDecl>().match(ToTU, Pattern);
+  auto ToProto = LastDeclMatcher<CXXRecordDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedDef == ToDef);
+  EXPECT_TRUE(ImportedProto == ToProto);
+  EXPECT_TRUE(ToDef->isThisDeclarationADefinition());
+  EXPECT_FALSE(ToProto->isThisDeclarationADefinition());
+  EXPECT_EQ(ToProto->getPreviousDecl(), ToDef);
+}
+
+TEST_P(ImportClasses, ImportPrototypeThenDefinition) {
+  Decl *FromTU0 = getTuDecl("class X;", Lang_CXX, "input0.cc");
+  Decl *FromTU1 = getTuDecl("class X {};", Lang_CXX, "input1.cc");
+  auto Pattern = cxxRecordDecl(hasName("X"), unless(isImplicit()));
+  auto FromProto = FirstDeclMatcher<CXXRecordDecl>().match(FromTU0, Pattern);
+  auto FromDef = FirstDeclMatcher<CXXRecordDecl>().match(FromTU1, Pattern);
+
+  Decl *ImportedProto = Import(FromProto, Lang_CXX);
+  Decl *ImportedDef = Import(FromDef, Lang_CXX);
+  Decl *ToTU = ImportedDef->getTranslationUnitDecl();
+
+  EXPECT_NE(ImportedDef, ImportedProto);
+  EXPECT_EQ(DeclCounter<CXXRecordDecl>().match(ToTU, Pattern), 2u);
+  auto ToProto = FirstDeclMatcher<CXXRecordDecl>().match(ToTU, Pattern);
+  auto ToDef = LastDeclMatcher<CXXRecordDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedDef == ToDef);
+  EXPECT_TRUE(ImportedProto == ToProto);
+  EXPECT_TRUE(ToDef->isThisDeclarationADefinition());
+  EXPECT_FALSE(ToProto->isThisDeclarationADefinition());
+  EXPECT_EQ(ToDef->getPreviousDecl(), ToProto);
+}
+
+struct ImportClassTemplates : ASTImporterTestBase {};
+
+TEST_P(ImportClassTemplates,
+       PrototypeShouldBeImportedAsAPrototypeWhenThereIsNoDefinition) {
+  Decl *FromTU = getTuDecl("template <class T> class X;", Lang_CXX);
+  auto Pattern = classTemplateDecl(hasName("X"), unless(isImplicit()));
+  auto FromD = FirstDeclMatcher<ClassTemplateDecl>().match(FromTU, Pattern);
+
+  Decl *ImportedD = Import(FromD, Lang_CXX);
+  Decl *ToTU = ImportedD->getTranslationUnitDecl();
+
+  EXPECT_EQ(DeclCounter<ClassTemplateDecl>().match(ToTU, Pattern), 1u);
+  auto ToD = LastDeclMatcher<ClassTemplateDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedD == ToD);
+  ASSERT_TRUE(ToD->getTemplatedDecl());
+  EXPECT_FALSE(ToD->isThisDeclarationADefinition());
+}
+
+TEST_P(ImportClassTemplates, ImportPrototypeAfterImportedPrototype) {
+  Decl *FromTU = getTuDecl(
+      "template <class T> class X; template <class T> class X;", Lang_CXX);
+  auto Pattern = classTemplateDecl(hasName("X"), unless(isImplicit()));
+  auto From0 = FirstDeclMatcher<ClassTemplateDecl>().match(FromTU, Pattern);
+  auto From1 = LastDeclMatcher<ClassTemplateDecl>().match(FromTU, Pattern);
+
+  Decl *Imported0 = Import(From0, Lang_CXX);
+  Decl *Imported1 = Import(From1, Lang_CXX);
+  Decl *ToTU = Imported0->getTranslationUnitDecl();
+
+  EXPECT_EQ(DeclCounter<ClassTemplateDecl>().match(ToTU, Pattern), 2u);
+  auto To0 = FirstDeclMatcher<ClassTemplateDecl>().match(ToTU, Pattern);
+  auto To1 = LastDeclMatcher<ClassTemplateDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(Imported0 == To0);
+  EXPECT_TRUE(Imported1 == To1);
+  ASSERT_TRUE(To0->getTemplatedDecl());
+  ASSERT_TRUE(To1->getTemplatedDecl());
+  EXPECT_FALSE(To0->isThisDeclarationADefinition());
+  EXPECT_FALSE(To1->isThisDeclarationADefinition());
+  EXPECT_EQ(To1->getPreviousDecl(), To0);
+  EXPECT_EQ(To1->getTemplatedDecl()->getPreviousDecl(),
+            To0->getTemplatedDecl());
+}
+
+TEST_P(ImportClassTemplates, DefinitionShouldBeImportedAsADefinition) {
+  Decl *FromTU = getTuDecl("template <class T> class X {};", Lang_CXX);
+  auto Pattern = classTemplateDecl(hasName("X"), unless(isImplicit()));
+  auto *FromD = FirstDeclMatcher<ClassTemplateDecl>().match(FromTU, Pattern);
+
+  Decl *ImportedD = Import(FromD, Lang_CXX);
+  Decl *ToTU = ImportedD->getTranslationUnitDecl();
+
+  EXPECT_EQ(DeclCounter<ClassTemplateDecl>().match(ToTU, Pattern), 1u);
+  auto ToD = LastDeclMatcher<ClassTemplateDecl>().match(ToTU, Pattern);
+  ASSERT_TRUE(ToD->getTemplatedDecl());
+  EXPECT_TRUE(ToD->isThisDeclarationADefinition());
+}
+
+TEST_P(ImportClassTemplates,
+       ImportPrototypeFromDifferentTUAfterImportedPrototype) {
+  Decl *FromTU0 =
+      getTuDecl("template <class T> class X;", Lang_CXX, "input0.cc");
+  Decl *FromTU1 =
+      getTuDecl("template <class T> class X;", Lang_CXX, "input1.cc");
+  auto Pattern = classTemplateDecl(hasName("X"), unless(isImplicit()));
+  auto From0 = FirstDeclMatcher<ClassTemplateDecl>().match(FromTU0, Pattern);
+  auto From1 = FirstDeclMatcher<ClassTemplateDecl>().match(FromTU1, Pattern);
+
+  Decl *Imported0 = Import(From0, Lang_CXX);
+  Decl *Imported1 = Import(From1, Lang_CXX);
+  Decl *ToTU = Imported0->getTranslationUnitDecl();
+
+  EXPECT_EQ(DeclCounter<ClassTemplateDecl>().match(ToTU, Pattern), 2u);
+  auto To0 = FirstDeclMatcher<ClassTemplateDecl>().match(ToTU, Pattern);
+  auto To1 = LastDeclMatcher<ClassTemplateDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(Imported0 == To0);
+  EXPECT_TRUE(Imported1 == To1);
+  ASSERT_TRUE(To0->getTemplatedDecl());
+  ASSERT_TRUE(To1->getTemplatedDecl());
+  EXPECT_FALSE(To0->isThisDeclarationADefinition());
+  EXPECT_FALSE(To1->isThisDeclarationADefinition());
+  EXPECT_EQ(To1->getPreviousDecl(), To0);
+  EXPECT_EQ(To1->getTemplatedDecl()->getPreviousDecl(),
+            To0->getTemplatedDecl());
+}
+
+TEST_P(ImportClassTemplates, ImportDefinitions) {
+  Decl *FromTU0 =
+      getTuDecl("template <class T> class X {};", Lang_CXX, "input0.cc");
+  Decl *FromTU1 =
+      getTuDecl("template <class T> class X {};", Lang_CXX, "input1.cc");
+  auto Pattern = classTemplateDecl(hasName("X"), unless(isImplicit()));
+  auto From0 = FirstDeclMatcher<ClassTemplateDecl>().match(FromTU0, Pattern);
+  auto From1 = FirstDeclMatcher<ClassTemplateDecl>().match(FromTU1, Pattern);
+
+  Decl *Imported0 = Import(From0, Lang_CXX);
+  Decl *Imported1 = Import(From1, Lang_CXX);
+  Decl *ToTU = Imported0->getTranslationUnitDecl();
+
+  EXPECT_EQ(Imported0, Imported1);
+  EXPECT_EQ(DeclCounter<ClassTemplateDecl>().match(ToTU, Pattern), 1u);
+  auto To0 = FirstDeclMatcher<ClassTemplateDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(Imported0 == To0);
+  ASSERT_TRUE(To0->getTemplatedDecl());
+  EXPECT_TRUE(To0->isThisDeclarationADefinition());
+}
+
+TEST_P(ImportClassTemplates, ImportDefinitionThenPrototype) {
+  Decl *FromTU0 =
+      getTuDecl("template <class T> class X {};", Lang_CXX, "input0.cc");
+  Decl *FromTU1 =
+      getTuDecl("template <class T> class X;", Lang_CXX, "input1.cc");
+  auto Pattern = classTemplateDecl(hasName("X"), unless(isImplicit()));
+  auto FromDef = FirstDeclMatcher<ClassTemplateDecl>().match(FromTU0, Pattern);
+  auto FromProto =
+      FirstDeclMatcher<ClassTemplateDecl>().match(FromTU1, Pattern);
+
+  Decl *ImportedDef = Import(FromDef, Lang_CXX);
+  Decl *ImportedProto = Import(FromProto, Lang_CXX);
+  Decl *ToTU = ImportedDef->getTranslationUnitDecl();
+
+  EXPECT_NE(ImportedDef, ImportedProto);
+  EXPECT_EQ(DeclCounter<ClassTemplateDecl>().match(ToTU, Pattern), 2u);
+  auto ToDef = FirstDeclMatcher<ClassTemplateDecl>().match(ToTU, Pattern);
+  auto ToProto = LastDeclMatcher<ClassTemplateDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedDef == ToDef);
+  EXPECT_TRUE(ImportedProto == ToProto);
+  ASSERT_TRUE(ToDef->getTemplatedDecl());
+  ASSERT_TRUE(ToProto->getTemplatedDecl());
+  EXPECT_TRUE(ToDef->isThisDeclarationADefinition());
+  EXPECT_FALSE(ToProto->isThisDeclarationADefinition());
+  EXPECT_EQ(ToProto->getPreviousDecl(), ToDef);
+  EXPECT_EQ(ToProto->getTemplatedDecl()->getPreviousDecl(),
+            ToDef->getTemplatedDecl());
+}
+
+TEST_P(ImportClassTemplates, ImportPrototypeThenDefinition) {
+  Decl *FromTU0 =
+      getTuDecl("template <class T> class X;", Lang_CXX, "input0.cc");
+  Decl *FromTU1 =
+      getTuDecl("template <class T> class X {};", Lang_CXX, "input1.cc");
+  auto Pattern = classTemplateDecl(hasName("X"), unless(isImplicit()));
+  auto FromProto =
+      FirstDeclMatcher<ClassTemplateDecl>().match(FromTU0, Pattern);
+  auto FromDef = FirstDeclMatcher<ClassTemplateDecl>().match(FromTU1, Pattern);
+
+  Decl *ImportedProto = Import(FromProto, Lang_CXX);
+  Decl *ImportedDef = Import(FromDef, Lang_CXX);
+  Decl *ToTU = ImportedDef->getTranslationUnitDecl();
+
+  EXPECT_NE(ImportedDef, ImportedProto);
+  EXPECT_EQ(DeclCounter<ClassTemplateDecl>().match(ToTU, Pattern), 2u);
+  auto ToProto = FirstDeclMatcher<ClassTemplateDecl>().match(ToTU, Pattern);
+  auto ToDef = LastDeclMatcher<ClassTemplateDecl>().match(ToTU, Pattern);
+  EXPECT_TRUE(ImportedDef == ToDef);
+  EXPECT_TRUE(ImportedProto == ToProto);
+  ASSERT_TRUE(ToProto->getTemplatedDecl());
+  ASSERT_TRUE(ToDef->getTemplatedDecl());
+  EXPECT_TRUE(ToDef->isThisDeclarationADefinition());
+  EXPECT_FALSE(ToProto->isThisDeclarationADefinition());
+  EXPECT_EQ(ToDef->getPreviousDecl(), ToProto);
+  EXPECT_EQ(ToDef->getTemplatedDecl()->getPreviousDecl(),
+            ToProto->getTemplatedDecl());
+}
+
+struct ImportFriendClasses : ASTImporterTestBase {};
+
+TEST_P(ImportFriendClasses, ImportOfFriendRecordDoesNotMergeDefinition) {
+  Decl *FromTU = getTuDecl(
+      R"(
+      class A {
+        template <int I> class F {};
+        class X {
+          template <int I> friend class F;
+        };
+      };
+      )",
+      Lang_CXX, "input0.cc");
+
+  auto *FromClass = FirstDeclMatcher<CXXRecordDecl>().match(
+      FromTU, cxxRecordDecl(hasName("F"), isDefinition()));
+  auto *FromFriendClass = LastDeclMatcher<CXXRecordDecl>().match(
+      FromTU, cxxRecordDecl(hasName("F")));
+
+  ASSERT_TRUE(FromClass);
+  ASSERT_TRUE(FromFriendClass);
+  ASSERT_NE(FromClass, FromFriendClass);
+  ASSERT_EQ(FromFriendClass->getDefinition(), FromClass);
+  ASSERT_EQ(FromFriendClass->getPreviousDecl(), FromClass);
+  ASSERT_EQ(FromFriendClass->getDescribedClassTemplate()->getPreviousDecl(),
+            FromClass->getDescribedClassTemplate());
+
+  auto *ToClass = cast<CXXRecordDecl>(Import(FromClass, Lang_CXX));
+  auto *ToFriendClass = cast<CXXRecordDecl>(Import(FromFriendClass, Lang_CXX));
+
+  EXPECT_TRUE(ToClass);
+  EXPECT_TRUE(ToFriendClass);
+  EXPECT_NE(ToClass, ToFriendClass);
+  EXPECT_EQ(ToFriendClass->getDefinition(), ToClass);
+  EXPECT_EQ(ToFriendClass->getPreviousDecl(), ToClass);
+  EXPECT_EQ(ToFriendClass->getDescribedClassTemplate()->getPreviousDecl(),
+            ToClass->getDescribedClassTemplate());
+}
+
+TEST_P(ImportFriendClasses, ImportOfRecursiveFriendClass) {
+  Decl *FromTu = getTuDecl(
+      R"(
+      class declToImport {
+        friend class declToImport;
+      };
+      )",
+      Lang_CXX, "input.cc");
+
+  auto *FromD = FirstDeclMatcher<CXXRecordDecl>().match(
+      FromTu, cxxRecordDecl(hasName("declToImport")));
+  auto *ToD = Import(FromD, Lang_CXX);
+  auto Pattern = cxxRecordDecl(has(friendDecl()));
+  ASSERT_TRUE(MatchVerifier<Decl>{}.match(FromD, Pattern));
+  EXPECT_TRUE(MatchVerifier<Decl>{}.match(ToD, Pattern));
+}
+
+TEST_P(ImportFriendClasses, ImportOfRecursiveFriendClassTemplate) {
+  Decl *FromTu = getTuDecl(
+      R"(
+      template<class A> class declToImport {
+        template<class A1> friend class declToImport;
+      };
+      )",
+      Lang_CXX, "input.cc");
+
+  auto *FromD =
+      FirstDeclMatcher<ClassTemplateDecl>().match(FromTu, classTemplateDecl());
+  auto *ToD = Import(FromD, Lang_CXX);
+
+  auto Pattern = classTemplateDecl(
+      has(cxxRecordDecl(has(friendDecl(has(classTemplateDecl()))))));
+  ASSERT_TRUE(MatchVerifier<Decl>{}.match(FromD, Pattern));
+  EXPECT_TRUE(MatchVerifier<Decl>{}.match(ToD, Pattern));
+
+  auto *Class =
+      FirstDeclMatcher<ClassTemplateDecl>().match(ToD, classTemplateDecl());
+  auto *Friend = FirstDeclMatcher<FriendDecl>().match(ToD, friendDecl());
+  EXPECT_NE(Friend->getFriendDecl(), Class);
+  EXPECT_EQ(Friend->getFriendDecl()->getPreviousDecl(), Class);
+}
+
+TEST_P(ImportFriendClasses, ProperPrevDeclForClassTemplateDecls) {
+  auto Pattern = classTemplateSpecializationDecl(hasName("X"));
+
+  ClassTemplateSpecializationDecl *Imported1;
+  {
+    Decl *FromTU = getTuDecl("template<class T> class X;"
+                             "struct Y { friend class X<int>; };",
+                             Lang_CXX, "input0.cc");
+    auto *FromD = FirstDeclMatcher<ClassTemplateSpecializationDecl>().match(
+        FromTU, Pattern);
+
+    Imported1 = cast<ClassTemplateSpecializationDecl>(Import(FromD, Lang_CXX));
+  }
+  ClassTemplateSpecializationDecl *Imported2;
+  {
+    Decl *FromTU = getTuDecl("template<class T> class X;"
+                             "template<> class X<int>{};"
+                             "struct Z { friend class X<int>; };",
+                             Lang_CXX, "input1.cc");
+    auto *FromD = FirstDeclMatcher<ClassTemplateSpecializationDecl>().match(
+        FromTU, Pattern);
+
+    Imported2 = cast<ClassTemplateSpecializationDecl>(Import(FromD, Lang_CXX));
+  }
+
+  Decl *ToTU = ToAST->getASTContext().getTranslationUnitDecl();
+  EXPECT_EQ(DeclCounter<ClassTemplateSpecializationDecl>().match(ToTU, Pattern),
+            2u);
+  ASSERT_TRUE(Imported2->getPreviousDecl());
+  EXPECT_EQ(Imported2->getPreviousDecl(), Imported1);
+}
+
+TEST_P(ImportFriendClasses, TypeForDeclShouldBeSetInTemplated) {
+  Decl *FromTU0 = getTuDecl(
+      R"(
+      class X {
+        class Y;
+      };
+      class X::Y {
+        template <typename T>
+        friend class F; // The decl context of F is the global namespace.
+      };
+      )",
+      Lang_CXX, "input0.cc");
+  auto *Fwd = FirstDeclMatcher<ClassTemplateDecl>().match(
+      FromTU0, classTemplateDecl(hasName("F")));
+  auto *Imported0 = cast<ClassTemplateDecl>(Import(Fwd, Lang_CXX));
+  Decl *FromTU1 = getTuDecl(
+      R"(
+      template <typename T>
+      class F {};
+      )",
+      Lang_CXX, "input1.cc");
+  auto *Definition = FirstDeclMatcher<ClassTemplateDecl>().match(
+      FromTU1, classTemplateDecl(hasName("F")));
+  auto *Imported1 = cast<ClassTemplateDecl>(Import(Definition, Lang_CXX));
+  EXPECT_EQ(Imported0->getTemplatedDecl()->getTypeForDecl(),
+            Imported1->getTemplatedDecl()->getTypeForDecl());
+}
+
+TEST_P(ImportFriendClasses, DeclsFromFriendsShouldBeInRedeclChains2) {
+  Decl *From, *To;
+  std::tie(From, To) =
+      getImportedDecl("class declToImport {};", Lang_CXX,
+                      "class Y { friend class declToImport; };", Lang_CXX);
+  auto *Imported = cast<CXXRecordDecl>(To);
+
+  EXPECT_TRUE(Imported->getPreviousDecl());
+}
+
+TEST_P(ImportFriendClasses,
+       ImportOfClassTemplateDefinitionShouldConnectToFwdFriend) {
+  Decl *ToTU = getToTuDecl(
+      R"(
+      class X {
+        class Y;
+      };
+      class X::Y {
+        template <typename T>
+        friend class F; // The decl context of F is the global namespace.
+      };
+      )",
+      Lang_CXX);
+  auto *ToDecl = FirstDeclMatcher<ClassTemplateDecl>().match(
+      ToTU, classTemplateDecl(hasName("F")));
+  Decl *FromTU = getTuDecl(
+      R"(
+      template <typename T>
+      class F {};
+      )",
+      Lang_CXX, "input0.cc");
+  auto *Definition = FirstDeclMatcher<ClassTemplateDecl>().match(
+      FromTU, classTemplateDecl(hasName("F")));
+  auto *ImportedDef = cast<ClassTemplateDecl>(Import(Definition, Lang_CXX));
+  EXPECT_TRUE(ImportedDef->getPreviousDecl());
+  EXPECT_EQ(ToDecl, ImportedDef->getPreviousDecl());
+  EXPECT_EQ(ToDecl->getTemplatedDecl(),
+            ImportedDef->getTemplatedDecl()->getPreviousDecl());
+}
+
+TEST_P(ImportFriendClasses,
+       ImportOfClassTemplateDefinitionAndFwdFriendShouldBeLinked) {
+  Decl *FromTU0 = getTuDecl(
+      R"(
+      class X {
+        class Y;
+      };
+      class X::Y {
+        template <typename T>
+        friend class F; // The decl context of F is the global namespace.
+      };
+      )",
+      Lang_CXX, "input0.cc");
+  auto *Fwd = FirstDeclMatcher<ClassTemplateDecl>().match(
+      FromTU0, classTemplateDecl(hasName("F")));
+  auto *ImportedFwd = cast<ClassTemplateDecl>(Import(Fwd, Lang_CXX));
+  Decl *FromTU1 = getTuDecl(
+      R"(
+      template <typename T>
+      class F {};
+      )",
+      Lang_CXX, "input1.cc");
+  auto *Definition = FirstDeclMatcher<ClassTemplateDecl>().match(
+      FromTU1, classTemplateDecl(hasName("F")));
+  auto *ImportedDef = cast<ClassTemplateDecl>(Import(Definition, Lang_CXX));
+  EXPECT_TRUE(ImportedDef->getPreviousDecl());
+  EXPECT_EQ(ImportedFwd, ImportedDef->getPreviousDecl());
+  EXPECT_EQ(ImportedFwd->getTemplatedDecl(),
+            ImportedDef->getTemplatedDecl()->getPreviousDecl());
+}
+
+TEST_P(ImportFriendClasses, ImportOfClassDefinitionAndFwdFriendShouldBeLinked) {
+  Decl *FromTU0 = getTuDecl(
+      R"(
+      class X {
+        class Y;
+      };
+      class X::Y {
+        friend class F; // The decl context of F is the global namespace.
+      };
+      )",
+      Lang_CXX, "input0.cc");
+  auto *Friend = FirstDeclMatcher<FriendDecl>().match(FromTU0, friendDecl());
+  QualType FT = Friend->getFriendType()->getType();
+  FT = FromTU0->getASTContext().getCanonicalType(FT);
+  auto *Fwd = cast<TagType>(FT)->getDecl();
+  auto *ImportedFwd = Import(Fwd, Lang_CXX);
+  Decl *FromTU1 = getTuDecl(
+      R"(
+      class F {};
+      )",
+      Lang_CXX, "input1.cc");
+  auto *Definition = FirstDeclMatcher<CXXRecordDecl>().match(
+      FromTU1, cxxRecordDecl(hasName("F")));
+  auto *ImportedDef = Import(Definition, Lang_CXX);
+  EXPECT_TRUE(ImportedDef->getPreviousDecl());
+  EXPECT_EQ(ImportedFwd, ImportedDef->getPreviousDecl());
+}
+
 struct DeclContextTest : ASTImporterTestBase {};
 
 TEST_P(DeclContextTest, removeDeclOfClassTemplateSpecialization) {
   Decl *TU = getTuDecl(
       R"(
       namespace NS {
 
       template <typename T>
TEST_P(DeclContextTest, removeDeclOfClassTemplateSpecialization) {
   auto *Spec = FirstDeclMatcher<ClassTemplateSpecializationDecl>().match(
       TU, classTemplateSpecializationDecl());
   ASSERT_TRUE(NS->containsDecl(Spec));
 
   NS->removeDecl(Spec);
   EXPECT_FALSE(NS->containsDecl(Spec));
 }
 
+TEST_P(DeclContextTest,
+       removeDeclShouldNotFailEvenIfWeHaveExternalVisibleStorage) {
+  Decl *TU = getTuDecl("extern int A; int A;", Lang_CXX);
+  auto *A0 = FirstDeclMatcher<VarDecl>().match(TU, varDecl(hasName("A")));
+  auto *A1 = LastDeclMatcher<VarDecl>().match(TU, varDecl(hasName("A")));
+
+  // Investigate the list.
+  auto *DC = A0->getDeclContext();
+  ASSERT_TRUE(DC->containsDecl(A0));
+  ASSERT_TRUE(DC->containsDecl(A1));
+
+  // Investigate the lookup table.
+  auto *Map = DC->getLookupPtr();
+  ASSERT_TRUE(Map);
+  auto I = Map->find(A0->getDeclName());
+  ASSERT_NE(I, Map->end());
+  StoredDeclsList &L = I->second;
+  // The lookup table contains the most recent decl of A.
+  ASSERT_NE(L.getAsDecl(), A0);
+  ASSERT_EQ(L.getAsDecl(), A1);
+
+  ASSERT_TRUE(L.getAsDecl());
+  // Simulate the private function DeclContext::reconcileExternalVisibleStorage.
+  // The point here is to have a Vec with only one element, which is not the
+  // one we are going to delete from the DC later.
+  L.setHasExternalDecls();
+  ASSERT_TRUE(L.getAsVector());
+  ASSERT_EQ(1u, L.getAsVector()->size());
+
+  // This asserts in the old implementation.
+  DC->removeDecl(A0);
+  EXPECT_FALSE(DC->containsDecl(A0));
+}
+
 struct ImportFunctionTemplateSpecializations : ASTImporterTestBase {};
 
 TEST_P(ImportFunctionTemplateSpecializations,
        TUshouldNotContainFunctionTemplateImplicitInstantiation) {
 
   Decl *FromTU = getTuDecl(
       R"(
       template<class T>
INSTANTIATE_TEST_CASE_P(ParameterizedTests, ASTImporterTestBase,
                         DefaultTestValuesForRunOptions, );
 
 INSTANTIATE_TEST_CASE_P(ParameterizedTests, ImportFunctions,
                         DefaultTestValuesForRunOptions, );
 
 INSTANTIATE_TEST_CASE_P(ParameterizedTests, ImportFriendFunctions,
                         DefaultTestValuesForRunOptions, );
 
+INSTANTIATE_TEST_CASE_P(ParameterizedTests, ImportClasses,
+                        DefaultTestValuesForRunOptions, );
+
+INSTANTIATE_TEST_CASE_P(ParameterizedTests, ImportClassTemplates,
+                        DefaultTestValuesForRunOptions, );
+
+INSTANTIATE_TEST_CASE_P(ParameterizedTests, ImportFriendClasses,
+                        DefaultTestValuesForRunOptions, );
+
 INSTANTIATE_TEST_CASE_P(ParameterizedTests,
                         ImportFunctionTemplateSpecializations,
                         DefaultTestValuesForRunOptions, );
 
 INSTANTIATE_TEST_CASE_P(ParameterizedTests, ImportImplicitMethods,
                         DefaultTestValuesForRunOptions, );
 
 INSTANTIATE_TEST_CASE_P(ParameterizedTests, ImportVariables,
                         DefaultTestValuesForRunOptions, );
 
 } // end namespace ast_matchers
 } // end namespace clang

unittests/AST/StructuralEquivalenceTest.cpp

TEST_F(StructuralEquivalenceRecordTest, UnnamedRecordsShouldBeInequivalent) {
   auto *R1 = getRecordDecl(Entry1);
 
   ASSERT_NE(R0, R1);
   EXPECT_TRUE(testStructuralMatch(R0, R0));
   EXPECT_TRUE(testStructuralMatch(R1, R1));
   EXPECT_FALSE(testStructuralMatch(R0, R1));
 }
 
+TEST_F(StructuralEquivalenceRecordTest, AnonymousRecordsShouldBeInequivalent) {
+  auto t = makeTuDecls(
+      R"(
+      struct X {
+        struct {
+          int a;
+        };
+        struct {
+          int b;
+        };
+      };
+      )",
+      "", Lang_C);
+  auto *TU = get<0>(t);
+  auto *A = FirstDeclMatcher<IndirectFieldDecl>().match(
+      TU, indirectFieldDecl(hasName("a")));
+  auto *FA = cast<FieldDecl>(A->chain().front());
+  RecordDecl *RA = cast<RecordType>(FA->getType().getTypePtr())->getDecl();
+  auto *B = FirstDeclMatcher<IndirectFieldDecl>().match(
+      TU, indirectFieldDecl(hasName("b")));
+  auto *FB = cast<FieldDecl>(B->chain().front());
+  RecordDecl *RB = cast<RecordType>(FB->getType().getTypePtr())->getDecl();
+
+  ASSERT_NE(RA, RB);
+  EXPECT_TRUE(testStructuralMatch(RA, RA));
+  EXPECT_TRUE(testStructuralMatch(RB, RB));
+  EXPECT_FALSE(testStructuralMatch(RA, RB));
+}
+
+TEST_F(StructuralEquivalenceRecordTest,
+       RecordsAreInequivalentIfOrderOfAnonRecordsIsDifferent) {
+  auto t = makeTuDecls(
+      R"(
+      struct X {
+        struct { int a; };
+        struct { int b; };
+      };
+      )",
+      R"(
+      struct X { // The order is reversed.
+        struct { int b; };
+        struct { int a; };
+      };
+      )",
+      Lang_C);
+
+  auto *TU = get<0>(t);
+  auto *A = FirstDeclMatcher<IndirectFieldDecl>().match(
+      TU, indirectFieldDecl(hasName("a")));
+  auto *FA = cast<FieldDecl>(A->chain().front());
+  RecordDecl *RA = cast<RecordType>(FA->getType().getTypePtr())->getDecl();
+
+  auto *TU1 = get<1>(t);
+  auto *A1 = FirstDeclMatcher<IndirectFieldDecl>().match(
+      TU1, indirectFieldDecl(hasName("a")));
+  auto *FA1 = cast<FieldDecl>(A1->chain().front());
+  RecordDecl *RA1 = cast<RecordType>(FA1->getType().getTypePtr())->getDecl();
+
+  RecordDecl *X =
+      FirstDeclMatcher<RecordDecl>().match(TU, recordDecl(hasName("X")));
+  RecordDecl *X1 =
+      FirstDeclMatcher<RecordDecl>().match(TU1, recordDecl(hasName("X")));
+  ASSERT_NE(X, X1);
+  EXPECT_FALSE(testStructuralMatch(X, X1));
+
+  ASSERT_NE(RA, RA1);
+  EXPECT_TRUE(testStructuralMatch(RA, RA));
+  EXPECT_TRUE(testStructuralMatch(RA1, RA1));
+  EXPECT_FALSE(testStructuralMatch(RA1, RA));
+}
+
 TEST_F(StructuralEquivalenceRecordTest,
        UnnamedRecordsShouldBeInequivalentEvenIfTheSecondIsBeingDefined) {
   auto Code =
       R"(
       struct A {
         struct {
           struct A *next;
         } entry0;