Function expression_tree_mutator

src/backend/nodes/nodeFuncs.c:2764–3570

 */

Node *
expression_tree_mutator(Node *node,
						Node *(*mutator) (),
						void *context)
{
	/*
	 * The mutator has already decided not to modify the current node, but we
	 * must call the mutator for any sub-nodes.
	 */

#define FLATCOPY(newnode, node, nodetype)  \
	( (newnode) = (nodetype *) palloc(sizeof(nodetype)), \
	  memcpy((newnode), (node), sizeof(nodetype)) )

#define CHECKFLATCOPY(newnode, node, nodetype)	\
	( AssertMacro(IsA((node), nodetype)), \
	  (newnode) = (nodetype *) palloc(sizeof(nodetype)), \
	  memcpy((newnode), (node), sizeof(nodetype)) )

#define MUTATE(newfield, oldfield, fieldtype)  \
		( (newfield) = (fieldtype) mutator((Node *) (oldfield), context) )

	if (node == NULL)
		return NULL;

	/* Guard against stack overflow due to overly complex expressions */
	check_stack_depth();

	switch (nodeTag(node))
	{
			/*
			 * Primitive node types with no expression subnodes.  Var and
			 * Const are frequent enough to deserve special cases, the others
			 * we just use copyObject for.
			 */
		case T_Var:
			{
				Var		   *var = (Var *) node;
				Var		   *newnode;

				FLATCOPY(newnode, var, Var);
				return (Node *) newnode;
			}
			break;
		case T_Const:
			{
				Const	   *oldnode = (Const *) node;
				Const	   *newnode;

				FLATCOPY(newnode, oldnode, Const);
				/* XXX we don't bother with datumCopy; should we? */
				return (Node *) newnode;
			}
			break;
		case T_RangeTblEntry: /* required by ORCA */
			return range_table_entry_mutator((RangeTblEntry *)node, mutator, context, 0);
		case T_Param:
		case T_CaseTestExpr: