Add a 'Base' type to RecursiveASTVisitor to make recursing easier and document

how you're supposed to use it.

llvm-svn: 103993

clang/include/clang/AST/RecursiveASTVisitor.h

@@ -43,11 +43,14 @@ return static_cast<Derived*>(this)->Visit ## NAME(static_cast<CLASS*>(Var))
    * and override any of the Visit* methods for declaration, type, statement,
    * expression, or other AST nodes where the visitor should customize
    * behavior.  Returning "true" from one of these overridden functions will
-   * abort the traversal.
+   * abort the entire traversal.  An overridden Visit* method will not descend
+   * further into the AST for that node unless Base::Visit* is called.
    */
   template<typename Derived>
   class RecursiveASTVisitor {
   public:
+    typedef RecursiveASTVisitor<Derived> Base;
+
     /// \brief Return a reference to the derived class.
     Derived &getDerived() { return *static_cast<Derived*>(this); }