DR101, PR12770: If a function is declared in the same context as a

using-declaration, and they declare the same function (either because
the using-declaration is in the same namespace as the declaration it
imports, or because they're both extern "C"), they do not conflict.

llvm-svn: 200897

1 files changed, 28 insertions, 12 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 995898aea48..8b750812d9c 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2268,8 +2268,8 @@ static bool haveIncompatibleLanguageLinkages(const T *Old, const T *New) {
 /// merged with.
 ///
 /// Returns true if there was an error, false otherwise.
-bool Sema::MergeFunctionDecl(FunctionDecl *New, Decl *OldD, Scope *S,
-                             bool MergeTypeWithOld) {
+bool Sema::MergeFunctionDecl(FunctionDecl *New, NamedDecl *&OldD,
+                             Scope *S, bool MergeTypeWithOld) {
   // Verify the old decl was also a function.
   FunctionDecl *Old = OldD->getAsFunction();
   if (!Old) {
@@ -2283,18 +2283,34 @@ bool Sema::MergeFunctionDecl(FunctionDecl *New, Decl *OldD, Scope *S,
         return true;
       }
 
-      Diag(New->getLocation(), diag::err_using_decl_conflict_reverse);
-      Diag(Shadow->getTargetDecl()->getLocation(),
-           diag::note_using_decl_target);
-      Diag(Shadow->getUsingDecl()->getLocation(),
-           diag::note_using_decl) << 0;
+      // C++11 [namespace.udecl]p14:
+      //   If a function declaration in namespace scope or block scope has the
+      //   same name and the same parameter-type-list as a function introduced
+      //   by a using-declaration, and the declarations do not declare the same
+      //   function, the program is ill-formed.
+
+      // Check whether the two declarations might declare the same function.
+      Old = dyn_cast<FunctionDecl>(Shadow->getTargetDecl());
+      if (Old &&
+          !Old->getDeclContext()->getRedeclContext()->Equals(
+              New->getDeclContext()->getRedeclContext()) &&
+          !(Old->isExternC() && New->isExternC()))
+        Old = 0;
+
+      if (!Old) {
+        Diag(New->getLocation(), diag::err_using_decl_conflict_reverse);
+        Diag(Shadow->getTargetDecl()->getLocation(),
+             diag::note_using_decl_target);
+        Diag(Shadow->getUsingDecl()->getLocation(), diag::note_using_decl) << 0;
+        return true;
+      }
+      OldD = Old;
+    } else {
+      Diag(New->getLocation(), diag::err_redefinition_different_kind)
+        << New->getDeclName();
+      Diag(OldD->getLocation(), diag::note_previous_definition);
       return true;
     }
-
-    Diag(New->getLocation(), diag::err_redefinition_different_kind)
-      << New->getDeclName();
-    Diag(OldD->getLocation(), diag::note_previous_definition);
-    return true;
   }
 
   // If the old declaration is invalid, just give up here.