[modules] Fix adding a templated friend functions to a namespace from another module.

When clang adds argument dependent lookup candidates, it can perform template
instantiation. For example, it can instantiate a templated friend function and
register it in the enclosing namespace's lookup table.

Fixes https://llvm.org/bugs/show_bug.cgi?id=24954

Reviewed by Richard Smith.

llvm-svn: 263634

1 files changed, 10 insertions, 2 deletions

diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index ee475d3cc52..3e04bc5ad7d 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -5751,8 +5751,16 @@ static bool isImportedDeclContext(ASTReader *Chain, const Decl *D) {
 }
 
 void ASTWriter::AddedVisibleDecl(const DeclContext *DC, const Decl *D) {
-  // TU and namespaces are handled elsewhere.
-  if (isa<TranslationUnitDecl>(DC) || isa<NamespaceDecl>(DC))
+  // TU is handled elsewhere.
+  if (isa<TranslationUnitDecl>(DC))
+    return;
+
+  // Namespaces are handled elsewhere, except for template instantiations of
+  // FunctionTemplateDecls in namespaces. We are interested in cases where the
+  // local instantiations are added to an imported context. Only happens when
+  // adding ADL lookup candidates, for example templated friends.
+  if (isa<NamespaceDecl>(DC) && D->getFriendObjectKind() == Decl::FOK_None &&
+      !isa<FunctionTemplateDecl>(D))
     return;
 
   // We're only interested in cases where a local declaration is added to an