4 files changed, 24 insertions, 0 deletions
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index d83b3ede38e..3aeb89559e7 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -176,6 +176,18 @@ void ASTDeclWriter::VisitDecl(Decl *D) {
   Record.push_back(D->getAccess());
   Record.push_back(D->isModulePrivate());
   Record.push_back(Writer.inferSubmoduleIDFromLocation(D->getLocation()));
+
+  // If this declaration injected a name into a context different from its
+  // lexical context, and that context is an imported namespace, we need to
+  // update its visible declarations to include this name.
+  //
+  // This happens when we instantiate a class with a friend declaration or a
+  // function with a local extern declaration, for instance.
+  if (D->isOutOfLine()) {
+    auto *NS = dyn_cast<NamespaceDecl>(D->getDeclContext()->getRedeclContext());
+    if (NS && NS->isFromASTFile())
+      Writer.AddUpdatedDeclContext(NS);
+  }
 }
 
 void ASTDeclWriter::VisitTranslationUnitDecl(TranslationUnitDecl *D) {
diff --git a/clang/test/Modules/Inputs/cxx-templates-a.h b/clang/test/Modules/Inputs/cxx-templates-a.h
index 0b1614d3d9e..6ecc2ca4610 100644
--- a/clang/test/Modules/Inputs/cxx-templates-a.h
+++ b/clang/test/Modules/Inputs/cxx-templates-a.h
@@ -48,3 +48,5 @@ template<typename T> struct MergeSpecializations<T*> {
 template<> struct MergeSpecializations<char> {
   typedef int explicitly_specialized_in_a;
 };
+
+void InstantiateWithFriend(Std::WithFriend<int> wfi) {}
diff --git a/clang/test/Modules/Inputs/cxx-templates-common.h b/clang/test/Modules/Inputs/cxx-templates-common.h
index 40a11e20b4f..77e3ddda36f 100644
--- a/clang/test/Modules/Inputs/cxx-templates-common.h
+++ b/clang/test/Modules/Inputs/cxx-templates-common.h
@@ -9,3 +9,9 @@ struct DefinedInCommon {
 template<typename T> struct CommonTemplate {
   enum E { a = 1, b = 2, c = 3 };
 };
+
+namespace Std {
+  template<typename T> struct WithFriend {
+    friend bool operator!=(const WithFriend &A, const WithFriend &B) { return false; }
+  };
+}
diff --git a/clang/test/Modules/cxx-templates.cpp b/clang/test/Modules/cxx-templates.cpp
index a1543888c39..d9331938acb 100644
--- a/clang/test/Modules/cxx-templates.cpp
+++ b/clang/test/Modules/cxx-templates.cpp
@@ -117,6 +117,10 @@ void testImplicitSpecialMembers(SomeTemplate<char[1]> &a,
   c = d;
 }
 
+bool testFriendInClassTemplate(Std::WithFriend<int> wfi) {
+  return wfi != wfi;
+}
+
 // CHECK-GLOBAL:      DeclarationName 'f'
 // CHECK-GLOBAL-NEXT: |-FunctionTemplate {{.*}} 'f'
 // CHECK-GLOBAL-NEXT: `-FunctionTemplate {{.*}} 'f'