Function expression_tree_walker

src/backend/nodes/nodeFuncs.c:1962–2461

 */

bool
expression_tree_walker(Node *node,
					   bool (*walker) (),
					   void *context)
{
	ListCell   *temp;

	/*
	 * The walker has already visited the current node, and so we need only
	 * recurse into any sub-nodes it has.
	 *
	 * We assume that the walker is not interested in List nodes per se, so
	 * when we expect a List we just recurse directly to self without
	 * bothering to call the walker.
	 */
	if (node == NULL)
		return false;

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

	switch (nodeTag(node))
	{
		case T_Var:
		case T_Const:
		case T_Param:
		case T_CaseTestExpr:
		case T_SQLValueFunction:
		case T_CoerceToDomainValue:
		case T_SetToDefault:
		case T_CurrentOfExpr:
		case T_NextValueExpr:
		case T_RangeTblRef:
		case T_SortGroupClause:
		case T_DMLActionExpr:
		case T_AggExprId:
		case T_RowIdExpr:
		case T_CTESearchClause:
		case T_Gather:
		case T_GatherMerge:
			/* primitive node types with no expression subnodes */
			break;
		case T_WithCheckOption:
			return walker(((WithCheckOption *) node)->qual, context);
		case T_Aggref:
			{
				Aggref	   *expr = (Aggref *) node;

				/* recurse directly on List */
				if (expression_tree_walker((Node *) expr->aggdirectargs,
										   walker, context))
					return true;
				if (expression_tree_walker((Node *) expr->args,
										   walker, context))
					return true;
				if (expression_tree_walker((Node *) expr->aggorder,
										   walker, context))
					return true;