Teach C++ name lookup that it's okay to look in a scope without a
context. This happens fairly rarely (which is why we got away with
this bug). Fixes PR6184, where we skipped over the template parameter
scope while tentatively parsing.

llvm-svn: 95376
diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index af1b8a2..3c8ab43 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -649,12 +649,9 @@
 
   for (; S; S = S->getParent()) {
     DeclContext *Ctx = static_cast<DeclContext *>(S->getEntity());
-    if (!Ctx || Ctx->isTransparentContext())
+    if (Ctx && Ctx->isTransparentContext())
       continue;
 
-    assert(Ctx && Ctx->isFileContext() &&
-           "We should have been looking only at file context here already.");
-
     // Check whether the IdResolver has anything in this scope.
     bool Found = false;
     for (; I != IEnd && S->isDeclScope(DeclPtrTy::make(*I)); ++I) {
@@ -668,16 +665,21 @@
       }
     }
 
-    // Look into context considering using-directives.
-    if (CppNamespaceLookup(R, Context, Ctx, UDirs))
-      Found = true;
+    if (Ctx) {
+      assert(Ctx->isFileContext() &&
+             "We should have been looking only at file context here already.");
+
+      // Look into context considering using-directives.
+      if (CppNamespaceLookup(R, Context, Ctx, UDirs))
+        Found = true;
+    }
 
     if (Found) {
       R.resolveKind();
       return true;
     }
 
-    if (R.isForRedeclaration() && !Ctx->isTransparentContext())
+    if (R.isForRedeclaration() && Ctx && !Ctx->isTransparentContext())
       return false;
   }