DR674, PR38883, PR40238: Qualified friend lookup should look for a

template specialization if there is no matching non-template function.

This exposed a couple of related bugs:
 - we would sometimes substitute into a friend template instead of a
   suitable non-friend declaration; this would now crash because we'd
   decide the specialization of the friend is a redeclaration of itself
 - ADL failed to properly handle the case where an invisible local
   extern declaration redeclares an invisible friend

Both are fixed herein: in particular, we now never make invisible
friends or local extern declarations visible to name lookup unless
they are the only declaration of the entity. (We already mostly did
this for local extern declarations.)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@350505 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 29 insertions, 0 deletions

diff --git a/lib/Sema/SemaOverload.cpp b/lib/Sema/SemaOverload.cpp
index 257eef435f..172116e30c 100644
--- a/lib/Sema/SemaOverload.cpp
+++ b/lib/Sema/SemaOverload.cpp
@@ -1041,6 +1041,35 @@ Sema::CheckOverload(Scope *S, FunctionDecl *New, const LookupResult &Old,
     }
   }
 
+  // C++ [temp.friend]p1:
+  //   For a friend function declaration that is not a template declaration:
+  //    -- if the name of the friend is a qualified or unqualified template-id,
+  //       [...], otherwise
+  //    -- if the name of the friend is a qualified-id and a matching
+  //       non-template function is found in the specified class or namespace,
+  //       the friend declaration refers to that function, otherwise,
+  //    -- if the name of the friend is a qualified-id and a matching function
+  //       template is found in the specified class or namespace, the friend
+  //       declaration refers to the deduced specialization of that function
+  //       template, otherwise
+  //    -- the name shall be an unqualified-id [...]
+  // If we get here for a qualified friend declaration, we've just reached the
+  // third bullet. If the type of the friend is dependent, skip this lookup
+  // until instantiation.
+  if (New->getFriendObjectKind() && New->getQualifier() &&
+      !New->getType()->isDependentType()) {
+    LookupResult TemplateSpecResult(LookupResult::Temporary, Old);
+    TemplateSpecResult.addAllDecls(Old);
+    if (CheckFunctionTemplateSpecialization(New, nullptr, TemplateSpecResult,
+                                            /*QualifiedFriend*/true)) {
+      New->setInvalidDecl();
+      return Ovl_Overload;
+    }
+
+    Match = TemplateSpecResult.getAsSingle<FunctionDecl>();
+    return Ovl_Match;
+  }
+
   return Ovl_Overload;
 }