Function checkWellFormedRecursionWalker

src/backend/parser/parse_cte.c:948–1144

* Tree walker function to detect invalid self-references in a recursive query. */

 * Tree walker function to detect invalid self-references in a recursive query.
 */
static bool
checkWellFormedRecursionWalker(Node *node, CteState *cstate)
{
	RecursionContext save_context = cstate->context;

	if (node == NULL)
		return false;
	if (IsA(node, RangeVar))
	{
		RangeVar   *rv = (RangeVar *) node;

		/* If unqualified name, might be a CTE reference */
		if (!rv->schemaname)
		{
			ListCell   *lc;
			CommonTableExpr *mycte;

			/* ... but first see if it's captured by an inner WITH */
			foreach(lc, cstate->innerwiths)
			{
				List	   *withlist = (List *) lfirst(lc);
				ListCell   *lc2;

				foreach(lc2, withlist)
				{
					CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc2);

					if (strcmp(rv->relname, cte->ctename) == 0)
						return false;	/* yes, so bail out */
				}
			}

			/* No, could be a reference to the query level we are working on */
			mycte = cstate->items[cstate->curitem].cte;
			if (strcmp(rv->relname, mycte->ctename) == 0)
			{
				/* Found a recursive reference to the active query */
				if (cstate->context != RECURSION_OK)
					ereport(ERROR,
							(errcode(ERRCODE_INVALID_RECURSION),
							 errmsg(recursion_errormsgs[cstate->context],
									mycte->ctename),
							 parser_errposition(cstate->pstate,
												rv->location)));
				/* Count references */
				if (++(cstate->selfrefcount) > 1)
					ereport(ERROR,
							(errcode(ERRCODE_INVALID_RECURSION),
							 errmsg("recursive reference to query \"%s\" must not appear more than once",
									mycte->ctename),
							 parser_errposition(cstate->pstate,
												rv->location)));
			}
		}
		return false;
	}
	if (IsA(node, SelectStmt))
	{