Check that the namespace alias doesn't conflict with a previous declaration in this scope.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@67921 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 24 insertions, 1 deletions

diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index 349aafdbda..4c8437deee 100644
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -1675,12 +1675,24 @@ void Sema::PushUsingDirective(Scope *S, UsingDirectiveDecl *UDir) {
     S->PushUsingDirective(UDir);
 }
 
-Sema::DeclTy *Sema::ActOnNamespaceAliasDef(Scope *CurScope, 
+Sema::DeclTy *Sema::ActOnNamespaceAliasDef(Scope *S, 
                                            SourceLocation AliasLoc,
                                            IdentifierInfo *Alias,
                                            const CXXScopeSpec &SS,
                                            SourceLocation NamespaceLoc,
                                            IdentifierInfo *NamespaceName) {
+  
+  // Check if we have a previous declaration with the same name.
+  if (NamedDecl *PrevDecl = LookupName(S, Alias, LookupOrdinaryName)) {
+    // FIXME: If this is a namespace alias decl, and it points to the same 
+    // namespace, we shouldn't warn.
+    unsigned DiagID = isa<NamespaceDecl>(PrevDecl) ? diag::err_redefinition :
+      diag::err_redefinition_different_kind;
+    Diag(AliasLoc, DiagID) << Alias;
+    Diag(PrevDecl->getLocation(), diag::note_previous_definition);
+    return 0;
+  }
+
   return 0;
 }
 
diff --git a/test/SemaCXX/namespace-alias.cpp b/test/SemaCXX/namespace-alias.cpp
new file mode 100644
index 0000000000..745893082b
--- /dev/null
+++ b/test/SemaCXX/namespace-alias.cpp
@@ -0,0 +1,11 @@
+// RUN: clang-cc -fsyntax-only -verify %s
+
+namespace N { };
+
+namespace A = N;
+
+int B; // expected-note {{previous definition is here}}
+namespace B = N; // expected-error {{redefinition of 'B' as different kind of symbol}}
+
+namespace C { } // expected-note {{previous definition is here}}
+namespace C = N; // expected-error {{redefinition of 'C'}}