Properly switch into the declaring scope of a template when performing
template argument deduction or (more importantly) the final substitution
required by such deduction.  Makes access control magically work in these
cases.

Fixes PR6967.

llvm-svn: 102572
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 6fdf243..7dee0ad 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -1167,8 +1167,7 @@
 
   // Enter the scope of this instantiation. We don't use
   // PushDeclContext because we don't have a scope.
-  DeclContext *PreviousContext = CurContext;
-  CurContext = Instantiation;
+  ContextRAII SavedContext(*this, Instantiation);
 
   // If this is an instantiation of a local class, merge this local
   // instantiation scope with the enclosing scope. Otherwise, every
@@ -1209,7 +1208,7 @@
     Invalid = true;
   
   // Exit the scope of this instantiation.
-  CurContext = PreviousContext;
+  SavedContext.pop();
 
   // If this is a polymorphic C++ class without a key function, we'll
   // have to mark all of the virtual members to allow emission of a vtable