1 files changed, 22 insertions, 3 deletions
diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index 8485ecd3a3..35935f994c 100644
--- a/lib/Sema/SemaTemplate.cpp
+++ b/lib/Sema/SemaTemplate.cpp
@@ -8104,9 +8104,13 @@ Sema::CheckDependentFunctionTemplateSpecialization(FunctionDecl *FD,
 ///
 /// \param Previous the set of declarations that may be specialized by
 /// this function specialization.
+///
+/// \param QualifiedFriend whether this is a lookup for a qualified friend
+/// declaration with no explicit template argument list that might be
+/// befriending a function template specialization.
 bool Sema::CheckFunctionTemplateSpecialization(
     FunctionDecl *FD, TemplateArgumentListInfo *ExplicitTemplateArgs,
-    LookupResult &Previous) {
+    LookupResult &Previous, bool QualifiedFriend) {
   // The set of function template specializations that could match this
   // explicit function template specialization.
   UnresolvedSet<8> Candidates;
@@ -8193,10 +8197,25 @@ bool Sema::CheckFunctionTemplateSpecialization(
     }
   }
 
+  // For a qualified friend declaration (with no explicit marker to indicate
+  // that a template specialization was intended), note all (template and
+  // non-template) candidates.
+  if (QualifiedFriend && Candidates.empty()) {
+    Diag(FD->getLocation(), diag::err_qualified_friend_no_match)
+        << FD->getDeclName() << FDLookupContext;
+    // FIXME: We should form a single candidate list and diagnose all
+    // candidates at once, to get proper sorting and limiting.
+    for (auto *OldND : Previous) {
+      if (auto *OldFD = dyn_cast<FunctionDecl>(OldND->getUnderlyingDecl()))
+        NoteOverloadCandidate(OldND, OldFD, FD->getType(), false);
+    }
+    FailedCandidates.NoteCandidates(*this, FD->getLocation());
+    return true;
+  }
+
   // Find the most specialized function template.
   UnresolvedSetIterator Result = getMostSpecialized(
-      Candidates.begin(), Candidates.end(), FailedCandidates,
-      FD->getLocation(),
+      Candidates.begin(), Candidates.end(), FailedCandidates, FD->getLocation(),
       PDiag(diag::err_function_template_spec_no_match) << FD->getDeclName(),
       PDiag(diag::err_function_template_spec_ambiguous)
           << FD->getDeclName() << (ExplicitTemplateArgs != nullptr),