[AST] Make RecursiveASTVisitor visit TemplateDecls in source order

[johannes]

Summary

This causes template arguments to be traversed before the templated
declaration, which is useful for clients that expect the nodes in
the same order as they are in the source code. Additionally, there
seems to be no good reason not to do so.

This was moved here from LexicallyOrderedRecursiveASTVisitor. The tests
still reside in LexicallyOrderedRecursiveASTVisitorTest.cpp under
VisitTemplateDecls.

[klimek]

LG

cfe/trunk/include/clang/AST/LexicallyOrderedRecursiveASTVisitor.h

for (auto I = DC->decls_begin(), E = DC->decls_end(); I != E;) {
           LexicallyNestedDeclarations.push_back(Sibling);
       }
       if (!BaseType::getDerived().TraverseDecl(Child))
         return false;
     }
     return true;
   }
 
-  bool shouldTraverseTemplateArgumentsBeforeDecl() const { return true; }
-
   Stmt::child_range getStmtChildren(Stmt *S) { return S->children(); }
 
   SmallVector<Stmt *, 8> getStmtChildren(CXXOperatorCallExpr *CE) {
     SmallVector<Stmt *, 8> Children(CE->children());
     bool Swap;
     // Switch the operator and the first operand for all infix and postfix
     // operations.
     switch (CE->getOperator()) {

cfe/trunk/include/clang/AST/RecursiveASTVisitor.h

#include "clang/Basic/OpenMPKinds.def"
   /// \brief Process clauses with list of variables.
   template <typename T> bool VisitOMPClauseList(T *Node);
   /// Process clauses with pre-initis.
   bool VisitOMPClauseWithPreInit(OMPClauseWithPreInit *Node);
   bool VisitOMPClauseWithPostUpdate(OMPClauseWithPostUpdate *Node);
 
   bool dataTraverseNode(Stmt *S, DataRecursionQueue *Queue);
   bool PostVisitStmt(Stmt *S);
-  bool shouldTraverseTemplateArgumentsBeforeDecl() const { return false; }
 };
 
 template <typename Derived>
 bool RecursiveASTVisitor<Derived>::dataTraverseNode(Stmt *S,
                                                     DataRecursionQueue *Queue) {
 #define DISPATCH_STMT(NAME, CLASS, VAR)                                        \
   return TRAVERSE_STMT_BASE(NAME, CLASS, VAR, Queue);
 
bool RecursiveASTVisitor<Derived>::TraverseTemplateInstantiations(
 
   return true;
 }
 
 // This macro unifies the traversal of class, variable and function
 // template declarations.
 #define DEF_TRAVERSE_TMPL_DECL(TMPLDECLKIND)                                   \
   DEF_TRAVERSE_DECL(TMPLDECLKIND##TemplateDecl, {                              \
-    if (getDerived().shouldTraverseTemplateArgumentsBeforeDecl()) {            \
-      TRY_TO(TraverseTemplateParameterListHelper(D->getTemplateParameters())); \
-      TRY_TO(TraverseDecl(D->getTemplatedDecl()));                             \
-    } else {                                                                   \
-      TRY_TO(TraverseDecl(D->getTemplatedDecl()));                             \
-      TRY_TO(TraverseTemplateParameterListHelper(D->getTemplateParameters())); \
-    }                                                                          \
+    TRY_TO(TraverseTemplateParameterListHelper(D->getTemplateParameters()));   \
+    TRY_TO(TraverseDecl(D->getTemplatedDecl()));                               \
                                                                                \
     /* By default, we do not traverse the instantiations of                    \
        class templates since they do not appear in the user code. The          \
        following code optionally traverses them.                               \
                                                                                \
        We only traverse the class instantiations when we see the canonical     \
        declaration of the template, to ensure we only visit them once. */      \
     if (getDerived().shouldVisitTemplateInstantiations() &&                    \