6 files changed, 26 insertions, 9 deletions

diff --git a/clang/include/clang/AST/Decl.h b/clang/include/clang/AST/Decl.h
index 6be323a981c..b1fe7b4c207 100644
--- a/clang/include/clang/AST/Decl.h
+++ b/clang/include/clang/AST/Decl.h
@@ -3424,6 +3424,8 @@ void Redeclarable<decl_type>::setPreviousDeclaration(decl_type *PrevDecl) {
 
     // If the declaration was previously visible, a redeclaration of it remains
     // visible even if it wouldn't be visible by itself.
+    // FIXME: Once we handle local extern decls properly, this should inherit
+    // the visibility from MostRecent, not from PrevDecl.
     static_cast<decl_type*>(this)->IdentifierNamespace |=
       PrevDecl->getIdentifierNamespace() &
       (Decl::IDNS_Ordinary | Decl::IDNS_Tag | Decl::IDNS_Type);
diff --git a/clang/include/clang/Serialization/ASTReader.h b/clang/include/clang/Serialization/ASTReader.h
index fff5cbca857..b5dfcd0b47b 100644
--- a/clang/include/clang/Serialization/ASTReader.h
+++ b/clang/include/clang/Serialization/ASTReader.h
@@ -907,9 +907,6 @@ private:
   /// the given canonical declaration.
   MergedDeclsMap::iterator
   combineStoredMergedDecls(Decl *Canon, serialization::GlobalDeclID CanonID);
-  
-  /// \brief Ready to load the previous declaration of the given Decl.
-  void loadAndAttachPreviousDecl(Decl *D, serialization::DeclID ID);
 
   /// \brief When reading a Stmt tree, Stmt operands are placed in this stack.
   SmallVector<Stmt *, 16> StmtStack;
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 99d6eaa3a03..122865b4686 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -2003,6 +2003,17 @@ void ASTDeclReader::attachPreviousDecl(Decl *D, Decl *previous) {
     RedeclarableTemplateDecl *TD = cast<RedeclarableTemplateDecl>(D);
     TD->RedeclLink.setNext(cast<RedeclarableTemplateDecl>(previous));
   }
+
+  // If the declaration was visible in one module, a redeclaration of it in
+  // another module remains visible even if it wouldn't be visible by itself.
+  //
+  // FIXME: In this case, the declaration should only be visible if a module
+  //        that makes it visible has been imported.
+  // FIXME: This is not correct in the case where previous is a local extern
+  //        declaration and D is a friend declaraton.
+  D->IdentifierNamespace |=
+      previous->IdentifierNamespace &
+      (Decl::IDNS_Ordinary | Decl::IDNS_Tag | Decl::IDNS_Type);
 }
 
 void ASTDeclReader::attachLatestDecl(Decl *D, Decl *Latest) {
@@ -2063,11 +2074,6 @@ ASTReader::combineStoredMergedDecls(Decl *Canon, GlobalDeclID CanonID) {
   return Pos;
 }
 
-void ASTReader::loadAndAttachPreviousDecl(Decl *D, serialization::DeclID ID) {
-  Decl *previous = GetDecl(ID);
-  ASTDeclReader::attachPreviousDecl(D, previous);
-}
-
 /// \brief Read the declaration at the given offset from the AST file.
 Decl *ASTReader::ReadDeclRecord(DeclID ID) {
   unsigned Index = ID - NUM_PREDEF_DECL_IDS;
@@ -2499,7 +2505,7 @@ void ASTReader::loadPendingDeclChain(serialization::GlobalDeclID ID) {
   for (unsigned I = 0, N = Chain.size(); I != N; ++I) {
     if (Chain[I] == CanonDecl)
       continue;
-    
+
     ASTDeclReader::attachPreviousDecl(Chain[I], MostRecent);
     MostRecent = Chain[I];
   }
diff --git a/clang/test/Modules/Inputs/cxx-templates-a.h b/clang/test/Modules/Inputs/cxx-templates-a.h
index aaafc1b1bdb..dbf12dacbae 100644
--- a/clang/test/Modules/Inputs/cxx-templates-a.h
+++ b/clang/test/Modules/Inputs/cxx-templates-a.h
@@ -22,3 +22,5 @@ template<typename T> void PerformDelayedLookup(T &t) {
 }
 
 template<typename T> void PerformDelayedLookupInDefaultArgument(T &t, int a = (FoundByADL(T()), 0)) {}
+
+template<typename T> struct RedeclaredAsFriend {};
diff --git a/clang/test/Modules/Inputs/cxx-templates-b.h b/clang/test/Modules/Inputs/cxx-templates-b.h
index 36d7d78c130..9bc76d5bbae 100644
--- a/clang/test/Modules/Inputs/cxx-templates-b.h
+++ b/clang/test/Modules/Inputs/cxx-templates-b.h
@@ -29,6 +29,12 @@ template<typename T> void UseDefinedInBImpl() {
 
 extern DefinedInBImpl &defined_in_b_impl;
 
+template<typename T>
+struct RedeclareTemplateAsFriend {
+  template<typename U>
+  friend struct RedeclaredAsFriend;
+};
+
 @import cxx_templates_a;
 template<typename T> void UseDefinedInBImplIndirectly(T &v) {
   PerformDelayedLookup(v);
diff --git a/clang/test/Modules/cxx-templates.cpp b/clang/test/Modules/cxx-templates.cpp
index 79052dd34bb..0949436b5d8 100644
--- a/clang/test/Modules/cxx-templates.cpp
+++ b/clang/test/Modules/cxx-templates.cpp
@@ -71,6 +71,10 @@ void g() {
   PerformDelayedLookup(defined_in_b_impl); // expected-note {{in instantiation of}}
 }
 
+RedeclaredAsFriend<int> raf1;
+RedeclareTemplateAsFriend<double> rtaf;
+RedeclaredAsFriend<double> raf2;
+
 @import cxx_templates_common;
 
 typedef SomeTemplate<int*> SomeTemplateIntPtr;