/*-------------------------------------------------------------------------
 *
 * parse_cte.c
 *	  handle CTEs (common table expressions) in parser
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/backend/parser/parse_cte.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "catalog/pg_collation.h"
#include "catalog/pg_type.h"
#include "nodes/nodeFuncs.h"
#include "parser/analyze.h"
#include "parser/parse_coerce.h"
#include "parser/parse_collate.h"
#include "parser/parse_cte.h"
#include "parser/parse_expr.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/typcache.h"


/* Enumeration of contexts in which a self-reference is disallowed */
typedef enum
{
	RECURSION_OK,
	RECURSION_NONRECURSIVETERM, /* inside the left-hand term */
	RECURSION_SUBLINK,			/* inside a sublink */
	RECURSION_OUTERJOIN,		/* inside nullable side of an outer join */
	RECURSION_INTERSECT,		/* underneath INTERSECT (ALL) */
	RECURSION_EXCEPT			/* underneath EXCEPT (ALL) */
} RecursionContext;

/* Associated error messages --- each must have one %s for CTE name */
static const char *const recursion_errormsgs[] = {
	/* RECURSION_OK */
	NULL,
	/* RECURSION_NONRECURSIVETERM */
	gettext_noop("recursive reference to query \"%s\" must not appear within its non-recursive term"),
	/* RECURSION_SUBLINK */
	gettext_noop("recursive reference to query \"%s\" must not appear within a subquery"),
	/* RECURSION_OUTERJOIN */
	gettext_noop("recursive reference to query \"%s\" must not appear within an outer join"),
	/* RECURSION_INTERSECT */
	gettext_noop("recursive reference to query \"%s\" must not appear within INTERSECT"),
	/* RECURSION_EXCEPT */
	gettext_noop("recursive reference to query \"%s\" must not appear within EXCEPT")
};

/*
 * For WITH RECURSIVE, we have to find an ordering of the clause members
 * with no forward references, and determine which members are recursive
 * (i.e., self-referential).  It is convenient to do this with an array
 * of CteItems instead of a list of CommonTableExprs.
 */
typedef struct CteItem
{
	CommonTableExpr *cte;		/* One CTE to examine */
	int			id;				/* Its ID number for dependencies */
	Bitmapset  *depends_on;		/* CTEs depended on (not including self) */
} CteItem;

/* CteState is what we need to pass around in the tree walkers */
typedef struct CteState
{
	/* global state: */
	ParseState *pstate;			/* global parse state */
	CteItem    *items;			/* array of CTEs and extra data */
	int			numitems;		/* number of CTEs */
	/* working state during a tree walk: */
	int			curitem;		/* index of item currently being examined */
	List	   *innerwiths;		/* list of lists of CommonTableExpr */
	/* working state for checkWellFormedRecursion walk only: */
	int			selfrefcount;	/* number of self-references detected */
	RecursionContext context;	/* context to allow or disallow self-ref */
} CteState;


static void analyzeCTE(ParseState *pstate, CommonTableExpr *cte);

/* Dependency processing functions */
static void makeDependencyGraph(CteState *cstate);
static bool makeDependencyGraphWalker(Node *node, CteState *cstate);
static void TopologicalSort(ParseState *pstate, CteItem *items, int numitems);

/* Recursion validity checker functions */
static void checkWellFormedRecursion(CteState *cstate);
static bool checkWellFormedRecursionWalker(Node *node, CteState *cstate);
static void checkWellFormedSelectStmt(SelectStmt *stmt, CteState *cstate);


/*
 * transformWithClause -
 *	  Transform the list of WITH clause "common table expressions" into
 *	  Query nodes.
 *
 * The result is the list of transformed CTEs to be put into the output
 * Query.  (This is in fact the same as the ending value of p_ctenamespace,
 * but it seems cleaner to not expose that in the function's API.)
 */
List *
transformWithClause(ParseState *pstate, WithClause *withClause)
{
	ListCell   *lc;

	/* Only one WITH clause per query level */
	Assert(pstate->p_ctenamespace == NIL);
	Assert(pstate->p_future_ctes == NIL);

	/*
	 * For either type of WITH, there must not be duplicate CTE names in the
	 * list.  Check this right away so we needn't worry later.
	 *
	 * Also, tentatively mark each CTE as non-recursive, and initialize its
	 * reference count to zero, and set pstate->p_hasModifyingCTE if needed.
	 */
	foreach(lc, withClause->ctes)
	{
		CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);
		ListCell   *rest;

		/* MERGE is allowed by parser, but unimplemented. Reject for now */
		if (IsA(cte->ctequery, MergeStmt))
			ereport(ERROR,
					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					errmsg("MERGE not supported in WITH query"),
					parser_errposition(pstate, cte->location));

		for_each_cell(rest, withClause->ctes, lnext(withClause->ctes, lc))
		{
			CommonTableExpr *cte2 = (CommonTableExpr *) lfirst(rest);

			if (strcmp(cte->ctename, cte2->ctename) == 0)
				ereport(ERROR,
						(errcode(ERRCODE_DUPLICATE_ALIAS),
						 errmsg("WITH query name \"%s\" specified more than once",
								cte2->ctename),
						 parser_errposition(pstate, cte2->location)));
		}

		cte->cterecursive = false;
		cte->cterefcount = 0;

		if (!IsA(cte->ctequery, SelectStmt))
		{
			/* must be a data-modifying statement */
			Assert(IsA(cte->ctequery, InsertStmt) ||
				   IsA(cte->ctequery, UpdateStmt) ||
				   IsA(cte->ctequery, DeleteStmt));

			pstate->p_hasModifyingCTE = true;
		}
	}

	if (withClause->recursive)
	{
		/*
		 * For WITH RECURSIVE, we rearrange the list elements if needed to
		 * eliminate forward references.  First, build a work array and set up
		 * the data structure needed by the tree walkers.
		 */
		CteState	cstate;
		int			i;

		cstate.pstate = pstate;
		cstate.numitems = list_length(withClause->ctes);
		cstate.items = (CteItem *) palloc0(cstate.numitems * sizeof(CteItem));
		i = 0;
		foreach(lc, withClause->ctes)
		{
			cstate.items[i].cte = (CommonTableExpr *) lfirst(lc);
			cstate.items[i].id = i;
			i++;
		}

		/*
		 * Find all the dependencies and sort the CteItems into a safe
		 * processing order.  Also, mark CTEs that contain self-references.
		 */
		makeDependencyGraph(&cstate);

		/*
		 * Check that recursive queries are well-formed.
		 */
		checkWellFormedRecursion(&cstate);

		/*
		 * Set up the ctenamespace for parse analysis.  Per spec, all the WITH
		 * items are visible to all others, so stuff them all in before parse
		 * analysis.  We build the list in safe processing order so that the
		 * planner can process the queries in sequence.
		 */
		for (i = 0; i < cstate.numitems; i++)
		{
			CommonTableExpr *cte = cstate.items[i].cte;

			pstate->p_ctenamespace = lappend(pstate->p_ctenamespace, cte);
		}

		/*
		 * Do parse analysis in the order determined by the topological sort.
		 */
		for (i = 0; i < cstate.numitems; i++)
		{
			CommonTableExpr *cte = cstate.items[i].cte;

			analyzeCTE(pstate, cte);
		}
	}
	else
	{
		/*
		 * For non-recursive WITH, just analyze each CTE in sequence and then
		 * add it to the ctenamespace.  This corresponds to the spec's
		 * definition of the scope of each WITH name.  However, to allow error
		 * reports to be aware of the possibility of an erroneous reference,
		 * we maintain a list in p_future_ctes of the not-yet-visible CTEs.
		 */
		pstate->p_future_ctes = list_copy(withClause->ctes);

		foreach(lc, withClause->ctes)
		{
			CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);

			analyzeCTE(pstate, cte);
			pstate->p_ctenamespace = lappend(pstate->p_ctenamespace, cte);
			pstate->p_future_ctes = list_delete_first(pstate->p_future_ctes);
		}
	}

	return pstate->p_ctenamespace;
}


/*
 * Perform the actual parse analysis transformation of one CTE.  All
 * CTEs it depends on have already been loaded into pstate->p_ctenamespace,
 * and have been marked with the correct output column names/types.
 */
static void
analyzeCTE(ParseState *pstate, CommonTableExpr *cte)
{
	Query	   *query;
	CTESearchClause *search_clause = cte->search_clause;
	CTECycleClause *cycle_clause = cte->cycle_clause;

	/* Analysis not done already */
	Assert(!IsA(cte->ctequery, Query));

	/*
	 * Before analyzing the CTE's query, we'd better identify the data type of
	 * the cycle mark column if any, since the query could refer to that.
	 * Other validity checks on the cycle clause will be done afterwards.
	 */
	if (cycle_clause)
	{
		TypeCacheEntry *typentry;
		Oid			op;

		cycle_clause->cycle_mark_value =
			transformExpr(pstate, cycle_clause->cycle_mark_value,
						  EXPR_KIND_CYCLE_MARK);
		cycle_clause->cycle_mark_default =
			transformExpr(pstate, cycle_clause->cycle_mark_default,
						  EXPR_KIND_CYCLE_MARK);

		cycle_clause->cycle_mark_type =
			select_common_type(pstate,
							   list_make2(cycle_clause->cycle_mark_value,
										  cycle_clause->cycle_mark_default),
							   "CYCLE", NULL);
		cycle_clause->cycle_mark_value =
			coerce_to_common_type(pstate,
								  cycle_clause->cycle_mark_value,
								  cycle_clause->cycle_mark_type,
								  "CYCLE/SET/TO");
		cycle_clause->cycle_mark_default =
			coerce_to_common_type(pstate,
								  cycle_clause->cycle_mark_default,
								  cycle_clause->cycle_mark_type,
								  "CYCLE/SET/DEFAULT");

		cycle_clause->cycle_mark_typmod =
			select_common_typmod(pstate,
								 list_make2(cycle_clause->cycle_mark_value,
											cycle_clause->cycle_mark_default),
								 cycle_clause->cycle_mark_type);

		cycle_clause->cycle_mark_collation =
			select_common_collation(pstate,
									list_make2(cycle_clause->cycle_mark_value,
											   cycle_clause->cycle_mark_default),
									true);

		/* Might as well look up the relevant <> operator while we are at it */
		typentry = lookup_type_cache(cycle_clause->cycle_mark_type,
									 TYPECACHE_EQ_OPR);
		if (!OidIsValid(typentry->eq_opr))
			ereport(ERROR,
					errcode(ERRCODE_UNDEFINED_FUNCTION),
					errmsg("could not identify an equality operator for type %s",
						   format_type_be(cycle_clause->cycle_mark_type)));
		op = get_negator(typentry->eq_opr);
		if (!OidIsValid(op))
			ereport(ERROR,
					errcode(ERRCODE_UNDEFINED_FUNCTION),
					errmsg("could not identify an inequality operator for type %s",
						   format_type_be(cycle_clause->cycle_mark_type)));

		cycle_clause->cycle_mark_neop = op;
	}

	/* Now we can get on with analyzing the CTE's query */
	query = parse_sub_analyze(cte->ctequery, pstate, cte, false, true);
	cte->ctequery = (Node *) query;

	/*
	 * Check that we got something reasonable.  These first two cases should
	 * be prevented by the grammar.
	 */
	if (!IsA(query, Query))
		elog(ERROR, "unexpected non-Query statement in WITH");
	if (query->utilityStmt != NULL)
		elog(ERROR, "unexpected utility statement in WITH");

	/*
	 * We disallow data-modifying WITH except at the top level of a query,
	 * because it's not clear when such a modification should be executed.
	 */
	if (query->commandType != CMD_SELECT &&
		pstate->parentParseState != NULL)
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("WITH clause containing a data-modifying statement must be at the top level"),
				 parser_errposition(pstate, cte->location)));

	/*
	 * CTE queries are always marked not canSetTag.  (Currently this only
	 * matters for data-modifying statements, for which the flag will be
	 * propagated to the ModifyTable plan node.)
	 */
	query->canSetTag = false;

	if (!cte->cterecursive)
	{
		/* Compute the output column names/types if not done yet */
		analyzeCTETargetList(pstate, cte, GetCTETargetList(cte));
	}
	else
	{
		/*
		 * Verify that the previously determined output column types and
		 * collations match what the query really produced.  We have to check
		 * this because the recursive term could have overridden the
		 * non-recursive term, and we don't have any easy way to fix that.
		 */
		ListCell   *lctlist,
				   *lctyp,
				   *lctypmod,
				   *lccoll;
		int			varattno;

		lctyp = list_head(cte->ctecoltypes);
		lctypmod = list_head(cte->ctecoltypmods);
		lccoll = list_head(cte->ctecolcollations);
		varattno = 0;
		foreach(lctlist, GetCTETargetList(cte))
		{
			TargetEntry *te = (TargetEntry *) lfirst(lctlist);
			Node	   *texpr;

			if (te->resjunk)
				continue;
			varattno++;
			Assert(varattno == te->resno);
			if (lctyp == NULL || lctypmod == NULL || lccoll == NULL)	/* shouldn't happen */
				elog(ERROR, "wrong number of output columns in WITH");
			texpr = (Node *) te->expr;
			if (exprType(texpr) != lfirst_oid(lctyp) ||
				exprTypmod(texpr) != lfirst_int(lctypmod))
				ereport(ERROR,
						(errcode(ERRCODE_DATATYPE_MISMATCH),
						 errmsg("recursive query \"%s\" column %d has type %s in non-recursive term but type %s overall",
								cte->ctename, varattno,
								format_type_with_typemod(lfirst_oid(lctyp),
														 lfirst_int(lctypmod)),
								format_type_with_typemod(exprType(texpr),
														 exprTypmod(texpr))),
						 errhint("Cast the output of the non-recursive term to the correct type."),
						 parser_errposition(pstate, exprLocation(texpr))));
			if (exprCollation(texpr) != lfirst_oid(lccoll))
				ereport(ERROR,
						(errcode(ERRCODE_COLLATION_MISMATCH),
						 errmsg("recursive query \"%s\" column %d has collation \"%s\" in non-recursive term but collation \"%s\" overall",
								cte->ctename, varattno,
								get_collation_name(lfirst_oid(lccoll)),
								get_collation_name(exprCollation(texpr))),
						 errhint("Use the COLLATE clause to set the collation of the non-recursive term."),
						 parser_errposition(pstate, exprLocation(texpr))));
			lctyp = lnext(cte->ctecoltypes, lctyp);
			lctypmod = lnext(cte->ctecoltypmods, lctypmod);
			lccoll = lnext(cte->ctecolcollations, lccoll);
		}
		if (lctyp != NULL || lctypmod != NULL || lccoll != NULL)	/* shouldn't happen */
			elog(ERROR, "wrong number of output columns in WITH");
	}

	/*
	 * Now make validity checks on the SEARCH and CYCLE clauses, if present.
	 */
	if (search_clause || cycle_clause)
	{
		Query	   *ctequery;
		SetOperationStmt *sos;

		if (!cte->cterecursive)
			ereport(ERROR,
					(errcode(ERRCODE_SYNTAX_ERROR),
					 errmsg("WITH query is not recursive"),
					 parser_errposition(pstate, cte->location)));

		/*
		 * SQL requires a WITH list element (CTE) to be "expandable" in order
		 * to allow a search or cycle clause.  That is a stronger requirement
		 * than just being recursive.  It basically means the query expression
		 * looks like
		 *
		 * non-recursive query UNION [ALL] recursive query
		 *
		 * and that the recursive query is not itself a set operation.
		 *
		 * As of this writing, most of these criteria are already satisfied by
		 * all recursive CTEs allowed by PostgreSQL.  In the future, if
		 * further variants recursive CTEs are accepted, there might be
		 * further checks required here to determine what is "expandable".
		 */

		ctequery = castNode(Query, cte->ctequery);
		Assert(ctequery->setOperations);
		sos = castNode(SetOperationStmt, ctequery->setOperations);

		/*
		 * This left side check is not required for expandability, but
		 * rewriteSearchAndCycle() doesn't currently have support for it, so
		 * we catch it here.
		 */
		if (!IsA(sos->larg, RangeTblRef))
			ereport(ERROR,
					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 errmsg("with a SEARCH or CYCLE clause, the left side of the UNION must be a SELECT")));

		if (!IsA(sos->rarg, RangeTblRef))
			ereport(ERROR,
					(errcode(ERRCODE_SYNTAX_ERROR),
					 errmsg("with a SEARCH or CYCLE clause, the right side of the UNION must be a SELECT")));
	}

	if (search_clause)
	{
		ListCell   *lc;
		List	   *seen = NIL;

		foreach(lc, search_clause->search_col_list)
		{
			String	   *colname = lfirst_node(String, lc);

			if (!list_member(cte->ctecolnames, colname))
				ereport(ERROR,
						(errcode(ERRCODE_SYNTAX_ERROR),
						 errmsg("search column \"%s\" not in WITH query column list",
								strVal(colname)),
						 parser_errposition(pstate, search_clause->location)));

			if (list_member(seen, colname))
				ereport(ERROR,
						(errcode(ERRCODE_DUPLICATE_COLUMN),
						 errmsg("search column \"%s\" specified more than once",
								strVal(colname)),
						 parser_errposition(pstate, search_clause->location)));
			seen = lappend(seen, colname);
		}

		if (list_member(cte->ctecolnames, makeString(search_clause->search_seq_column)))
			ereport(ERROR,
					errcode(ERRCODE_SYNTAX_ERROR),
					errmsg("search sequence column name \"%s\" already used in WITH query column list",
						   search_clause->search_seq_column),
					parser_errposition(pstate, search_clause->location));
	}

	if (cycle_clause)
	{
		ListCell   *lc;
		List	   *seen = NIL;

		foreach(lc, cycle_clause->cycle_col_list)
		{
			String	   *colname = lfirst_node(String, lc);

			if (!list_member(cte->ctecolnames, colname))
				ereport(ERROR,
						(errcode(ERRCODE_SYNTAX_ERROR),
						 errmsg("cycle column \"%s\" not in WITH query column list",
								strVal(colname)),
						 parser_errposition(pstate, cycle_clause->location)));

			if (list_member(seen, colname))
				ereport(ERROR,
						(errcode(ERRCODE_DUPLICATE_COLUMN),
						 errmsg("cycle column \"%s\" specified more than once",
								strVal(colname)),
						 parser_errposition(pstate, cycle_clause->location)));
			seen = lappend(seen, colname);
		}

		if (list_member(cte->ctecolnames, makeString(cycle_clause->cycle_mark_column)))
			ereport(ERROR,
					errcode(ERRCODE_SYNTAX_ERROR),
					errmsg("cycle mark column name \"%s\" already used in WITH query column list",
						   cycle_clause->cycle_mark_column),
					parser_errposition(pstate, cycle_clause->location));

		if (list_member(cte->ctecolnames, makeString(cycle_clause->cycle_path_column)))
			ereport(ERROR,
					errcode(ERRCODE_SYNTAX_ERROR),
					errmsg("cycle path column name \"%s\" already used in WITH query column list",
						   cycle_clause->cycle_path_column),
					parser_errposition(pstate, cycle_clause->location));

		if (strcmp(cycle_clause->cycle_mark_column,
				   cycle_clause->cycle_path_column) == 0)
			ereport(ERROR,
					errcode(ERRCODE_SYNTAX_ERROR),
					errmsg("cycle mark column name and cycle path column name are the same"),
					parser_errposition(pstate, cycle_clause->location));
	}

	if (search_clause && cycle_clause)
	{
		if (strcmp(search_clause->search_seq_column,
				   cycle_clause->cycle_mark_column) == 0)
			ereport(ERROR,
					errcode(ERRCODE_SYNTAX_ERROR),
					errmsg("search sequence column name and cycle mark column name are the same"),
					parser_errposition(pstate, search_clause->location));

		if (strcmp(search_clause->search_seq_column,
				   cycle_clause->cycle_path_column) == 0)
			ereport(ERROR,
					errcode(ERRCODE_SYNTAX_ERROR),
					errmsg("search sequence column name and cycle path column name are the same"),
					parser_errposition(pstate, search_clause->location));
	}
}

/*
 * Compute derived fields of a CTE, given the transformed output targetlist
 *
 * For a nonrecursive CTE, this is called after transforming the CTE's query.
 * For a recursive CTE, we call it after transforming the non-recursive term,
 * and pass the targetlist emitted by the non-recursive term only.
 *
 * Note: in the recursive case, the passed pstate is actually the one being
 * used to analyze the CTE's query, so it is one level lower down than in
 * the nonrecursive case.  This doesn't matter since we only use it for
 * error message context anyway.
 */
void
analyzeCTETargetList(ParseState *pstate, CommonTableExpr *cte, List *tlist)
{
	int			numaliases;
	int			varattno;
	ListCell   *tlistitem;

	/* Not done already ... */
	Assert(cte->ctecolnames == NIL);

	/*
	 * We need to determine column names, types, and collations.  The alias
	 * column names override anything coming from the query itself.  (Note:
	 * the SQL spec says that the alias list must be empty or exactly as long
	 * as the output column set; but we allow it to be shorter for consistency
	 * with Alias handling.)
	 */
	cte->ctecolnames = copyObject(cte->aliascolnames);
	cte->ctecoltypes = cte->ctecoltypmods = cte->ctecolcollations = NIL;
	numaliases = list_length(cte->aliascolnames);
	varattno = 0;
	foreach(tlistitem, tlist)
	{
		TargetEntry *te = (TargetEntry *) lfirst(tlistitem);
		Oid			coltype;
		int32		coltypmod;
		Oid			colcoll;

		if (te->resjunk)
			continue;
		varattno++;
		Assert(varattno == te->resno);
		if (varattno > numaliases)
		{
			char	   *attrname;

			attrname = pstrdup(te->resname);
			cte->ctecolnames = lappend(cte->ctecolnames, makeString(attrname));
		}
		coltype = exprType((Node *) te->expr);
		coltypmod = exprTypmod((Node *) te->expr);
		colcoll = exprCollation((Node *) te->expr);

		/*
		 * If the CTE is recursive, force the exposed column type of any
		 * "unknown" column to "text".  We must deal with this here because
		 * we're called on the non-recursive term before there's been any
		 * attempt to force unknown output columns to some other type.  We
		 * have to resolve unknowns before looking at the recursive term.
		 *
		 * The column might contain 'foo' COLLATE "bar", so don't override
		 * collation if it's already set.
		 */
		if (cte->cterecursive && coltype == UNKNOWNOID)
		{
			coltype = TEXTOID;
			coltypmod = -1;		/* should be -1 already, but be sure */
			if (!OidIsValid(colcoll))
				colcoll = DEFAULT_COLLATION_OID;
		}
		cte->ctecoltypes = lappend_oid(cte->ctecoltypes, coltype);
		cte->ctecoltypmods = lappend_int(cte->ctecoltypmods, coltypmod);
		cte->ctecolcollations = lappend_oid(cte->ctecolcollations, colcoll);
	}
	if (varattno < numaliases)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
				 errmsg("WITH query \"%s\" has %d columns available but %d columns specified",
						cte->ctename, varattno, numaliases),
				 parser_errposition(pstate, cte->location)));
}


/*
 * Identify the cross-references of a list of WITH RECURSIVE items,
 * and sort into an order that has no forward references.
 */
static void
makeDependencyGraph(CteState *cstate)
{
	int			i;

	for (i = 0; i < cstate->numitems; i++)
	{
		CommonTableExpr *cte = cstate->items[i].cte;

		cstate->curitem = i;
		cstate->innerwiths = NIL;
		makeDependencyGraphWalker((Node *) cte->ctequery, cstate);
		Assert(cstate->innerwiths == NIL);
	}

	TopologicalSort(cstate->pstate, cstate->items, cstate->numitems);
}

/*
 * Tree walker function to detect cross-references and self-references of the
 * CTEs in a WITH RECURSIVE list.
 */
static bool
makeDependencyGraphWalker(Node *node, CteState *cstate)
{
	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;
			int			i;

			/* ... 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 */
			for (i = 0; i < cstate->numitems; i++)
			{
				CommonTableExpr *cte = cstate->items[i].cte;

				if (strcmp(rv->relname, cte->ctename) == 0)
				{
					int			myindex = cstate->curitem;

					if (i != myindex)
					{
						/* Add cross-item dependency */
						cstate->items[myindex].depends_on =
							bms_add_member(cstate->items[myindex].depends_on,
										   cstate->items[i].id);
					}
					else
					{
						/* Found out this one is self-referential */
						cte->cterecursive = true;
					}
					break;
				}
			}
		}
		return false;
	}
	if (IsA(node, SelectStmt))
	{
		SelectStmt *stmt = (SelectStmt *) node;
		ListCell   *lc;

		if (stmt->withClause)
		{
			if (stmt->withClause->recursive)
			{
				/*
				 * In the RECURSIVE case, all query names of the WITH are
				 * visible to all WITH items as well as the main query. So
				 * push them all on, process, pop them all off.
				 */
				cstate->innerwiths = lcons(stmt->withClause->ctes,
										   cstate->innerwiths);
				foreach(lc, stmt->withClause->ctes)
				{
					CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);

					(void) makeDependencyGraphWalker(cte->ctequery, cstate);
				}
				(void) raw_expression_tree_walker(node,
												  makeDependencyGraphWalker,
												  (void *) cstate);
				cstate->innerwiths = list_delete_first(cstate->innerwiths);
			}
			else
			{
				/*
				 * In the non-RECURSIVE case, query names are visible to the
				 * WITH items after them and to the main query.
				 */
				cstate->innerwiths = lcons(NIL, cstate->innerwiths);
				foreach(lc, stmt->withClause->ctes)
				{
					CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);
					ListCell   *cell1;

					(void) makeDependencyGraphWalker(cte->ctequery, cstate);
					/* note that recursion could mutate innerwiths list */
					cell1 = list_head(cstate->innerwiths);
					lfirst(cell1) = lappend((List *) lfirst(cell1), cte);
				}
				(void) raw_expression_tree_walker(node,
												  makeDependencyGraphWalker,
												  (void *) cstate);
				cstate->innerwiths = list_delete_first(cstate->innerwiths);
			}
			/* We're done examining the SelectStmt */
			return false;
		}
		/* if no WITH clause, just fall through for normal processing */
	}
	if (IsA(node, WithClause))
	{
		/*
		 * Prevent raw_expression_tree_walker from recursing directly into a
		 * WITH clause.  We need that to happen only under the control of the
		 * code above.
		 */
		return false;
	}
	return raw_expression_tree_walker(node,
									  makeDependencyGraphWalker,
									  (void *) cstate);
}

/*
 * Sort by dependencies, using a standard topological sort operation
 */
static void
TopologicalSort(ParseState *pstate, CteItem *items, int numitems)
{
	int			i,
				j;

	/* for each position in sequence ... */
	for (i = 0; i < numitems; i++)
	{
		/* ... scan the remaining items to find one that has no dependencies */
		for (j = i; j < numitems; j++)
		{
			if (bms_is_empty(items[j].depends_on))
				break;
		}

		/* if we didn't find one, the dependency graph has a cycle */
		if (j >= numitems)
			ereport(ERROR,
					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 errmsg("mutual recursion between WITH items is not implemented"),
					 parser_errposition(pstate, items[i].cte->location)));

		/*
		 * Found one.  Move it to front and remove it from every other item's
		 * dependencies.
		 */
		if (i != j)
		{
			CteItem		tmp;

			tmp = items[i];
			items[i] = items[j];
			items[j] = tmp;
		}

		/*
		 * Items up through i are known to have no dependencies left, so we
		 * can skip them in this loop.
		 */
		for (j = i + 1; j < numitems; j++)
		{
			items[j].depends_on = bms_del_member(items[j].depends_on,
												 items[i].id);
		}
	}
}


/*
 * Check that recursive queries are well-formed.
 */
static void
checkWellFormedRecursion(CteState *cstate)
{
	int			i;

	for (i = 0; i < cstate->numitems; i++)
	{
		CommonTableExpr *cte = cstate->items[i].cte;
		SelectStmt *stmt = (SelectStmt *) cte->ctequery;

		Assert(!IsA(stmt, Query));	/* not analyzed yet */

		/* Ignore items that weren't found to be recursive */
		if (!cte->cterecursive)
			continue;

		/* Must be a SELECT statement */
		if (!IsA(stmt, SelectStmt))
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_RECURSION),
					 errmsg("recursive query \"%s\" must not contain data-modifying statements",
							cte->ctename),
					 parser_errposition(cstate->pstate, cte->location)));

		/* Must have top-level UNION */
		if (stmt->op != SETOP_UNION)
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_RECURSION),
					 errmsg("recursive query \"%s\" does not have the form non-recursive-term UNION [ALL] recursive-term",
							cte->ctename),
					 parser_errposition(cstate->pstate, cte->location)));

		/* The left-hand operand mustn't contain self-reference at all */
		cstate->curitem = i;
		cstate->innerwiths = NIL;
		cstate->selfrefcount = 0;
		cstate->context = RECURSION_NONRECURSIVETERM;
		checkWellFormedRecursionWalker((Node *) stmt->larg, cstate);
		Assert(cstate->innerwiths == NIL);

		/* Right-hand operand should contain one reference in a valid place */
		cstate->curitem = i;
		cstate->innerwiths = NIL;
		cstate->selfrefcount = 0;
		cstate->context = RECURSION_OK;
		checkWellFormedRecursionWalker((Node *) stmt->rarg, cstate);
		Assert(cstate->innerwiths == NIL);
		if (cstate->selfrefcount != 1)	/* shouldn't happen */
			elog(ERROR, "missing recursive reference");

		/* WITH mustn't contain self-reference, either */
		if (stmt->withClause)
		{
			cstate->curitem = i;
			cstate->innerwiths = NIL;
			cstate->selfrefcount = 0;
			cstate->context = RECURSION_SUBLINK;
			checkWellFormedRecursionWalker((Node *) stmt->withClause->ctes,
										   cstate);
			Assert(cstate->innerwiths == NIL);
		}

		/*
		 * Disallow ORDER BY and similar decoration atop the UNION. These
		 * don't make sense because it's impossible to figure out what they
		 * mean when we have only part of the recursive query's results. (If
		 * we did allow them, we'd have to check for recursive references
		 * inside these subtrees.)
		 */
		if (stmt->sortClause)
			ereport(ERROR,
					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 errmsg("ORDER BY in a recursive query is not implemented"),
					 parser_errposition(cstate->pstate,
										exprLocation((Node *) stmt->sortClause))));
		if (stmt->limitOffset)
			ereport(ERROR,
					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 errmsg("OFFSET in a recursive query is not implemented"),
					 parser_errposition(cstate->pstate,
										exprLocation(stmt->limitOffset))));
		if (stmt->limitCount)
			ereport(ERROR,
					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 errmsg("LIMIT in a recursive query is not implemented"),
					 parser_errposition(cstate->pstate,
										exprLocation(stmt->limitCount))));
		if (stmt->lockingClause)
			ereport(ERROR,
					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 errmsg("FOR UPDATE/SHARE in a recursive query is not implemented"),
					 parser_errposition(cstate->pstate,
										exprLocation((Node *) stmt->lockingClause))));
	}
}

/*
 * 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))
	{
		SelectStmt *stmt = (SelectStmt *) node;
		ListCell   *lc;

		if (stmt->withClause)
		{
			if (stmt->withClause->recursive)
			{
				/*
				 * In the RECURSIVE case, all query names of the WITH are
				 * visible to all WITH items as well as the main query. So
				 * push them all on, process, pop them all off.
				 */
				cstate->innerwiths = lcons(stmt->withClause->ctes,
										   cstate->innerwiths);
				foreach(lc, stmt->withClause->ctes)
				{
					CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);

					(void) checkWellFormedRecursionWalker(cte->ctequery, cstate);
				}
				checkWellFormedSelectStmt(stmt, cstate);
				cstate->innerwiths = list_delete_first(cstate->innerwiths);
			}
			else
			{
				/*
				 * In the non-RECURSIVE case, query names are visible to the
				 * WITH items after them and to the main query.
				 */
				cstate->innerwiths = lcons(NIL, cstate->innerwiths);
				foreach(lc, stmt->withClause->ctes)
				{
					CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);
					ListCell   *cell1;

					(void) checkWellFormedRecursionWalker(cte->ctequery, cstate);
					/* note that recursion could mutate innerwiths list */
					cell1 = list_head(cstate->innerwiths);
					lfirst(cell1) = lappend((List *) lfirst(cell1), cte);
				}
				checkWellFormedSelectStmt(stmt, cstate);
				cstate->innerwiths = list_delete_first(cstate->innerwiths);
			}
		}
		else
			checkWellFormedSelectStmt(stmt, cstate);
		/* We're done examining the SelectStmt */
		return false;
	}
	if (IsA(node, WithClause))
	{
		/*
		 * Prevent raw_expression_tree_walker from recursing directly into a
		 * WITH clause.  We need that to happen only under the control of the
		 * code above.
		 */
		return false;
	}
	if (IsA(node, JoinExpr))
	{
		JoinExpr   *j = (JoinExpr *) node;

		switch (j->jointype)
		{
			case JOIN_INNER:
				checkWellFormedRecursionWalker(j->larg, cstate);
				checkWellFormedRecursionWalker(j->rarg, cstate);
				checkWellFormedRecursionWalker(j->quals, cstate);
				break;
			case JOIN_LEFT:
				checkWellFormedRecursionWalker(j->larg, cstate);
				if (save_context == RECURSION_OK)
					cstate->context = RECURSION_OUTERJOIN;
				checkWellFormedRecursionWalker(j->rarg, cstate);
				cstate->context = save_context;
				checkWellFormedRecursionWalker(j->quals, cstate);
				break;
			case JOIN_FULL:
				if (save_context == RECURSION_OK)
					cstate->context = RECURSION_OUTERJOIN;
				checkWellFormedRecursionWalker(j->larg, cstate);
				checkWellFormedRecursionWalker(j->rarg, cstate);
				cstate->context = save_context;
				checkWellFormedRecursionWalker(j->quals, cstate);
				break;
			case JOIN_RIGHT:
				if (save_context == RECURSION_OK)
					cstate->context = RECURSION_OUTERJOIN;
				checkWellFormedRecursionWalker(j->larg, cstate);
				cstate->context = save_context;
				checkWellFormedRecursionWalker(j->rarg, cstate);
				checkWellFormedRecursionWalker(j->quals, cstate);
				break;
			default:
				elog(ERROR, "unrecognized join type: %d",
					 (int) j->jointype);
		}
		return false;
	}
	if (IsA(node, SubLink))
	{
		SubLink    *sl = (SubLink *) node;

		/*
		 * we intentionally override outer context, since subquery is
		 * independent
		 */
		cstate->context = RECURSION_SUBLINK;
		checkWellFormedRecursionWalker(sl->subselect, cstate);
		cstate->context = save_context;
		checkWellFormedRecursionWalker(sl->testexpr, cstate);
		return false;
	}
	return raw_expression_tree_walker(node,
									  checkWellFormedRecursionWalker,
									  (void *) cstate);
}

/*
 * subroutine for checkWellFormedRecursionWalker: process a SelectStmt
 * without worrying about its WITH clause
 */
static void
checkWellFormedSelectStmt(SelectStmt *stmt, CteState *cstate)
{
	RecursionContext save_context = cstate->context;

	if (save_context != RECURSION_OK)
	{
		/* just recurse without changing state */
		raw_expression_tree_walker((Node *) stmt,
								   checkWellFormedRecursionWalker,
								   (void *) cstate);
	}
	else
	{
		switch (stmt->op)
		{
			case SETOP_NONE:
			case SETOP_UNION:
				raw_expression_tree_walker((Node *) stmt,
										   checkWellFormedRecursionWalker,
										   (void *) cstate);
				break;
			case SETOP_INTERSECT:
				if (stmt->all)
					cstate->context = RECURSION_INTERSECT;
				checkWellFormedRecursionWalker((Node *) stmt->larg,
											   cstate);
				checkWellFormedRecursionWalker((Node *) stmt->rarg,
											   cstate);
				cstate->context = save_context;
				checkWellFormedRecursionWalker((Node *) stmt->sortClause,
											   cstate);
				checkWellFormedRecursionWalker((Node *) stmt->limitOffset,
											   cstate);
				checkWellFormedRecursionWalker((Node *) stmt->limitCount,
											   cstate);
				checkWellFormedRecursionWalker((Node *) stmt->lockingClause,
											   cstate);
				/* stmt->withClause is intentionally ignored here */
				break;
			case SETOP_EXCEPT:
				if (stmt->all)
					cstate->context = RECURSION_EXCEPT;
				checkWellFormedRecursionWalker((Node *) stmt->larg,
											   cstate);
				cstate->context = RECURSION_EXCEPT;
				checkWellFormedRecursionWalker((Node *) stmt->rarg,
											   cstate);
				cstate->context = save_context;
				checkWellFormedRecursionWalker((Node *) stmt->sortClause,
											   cstate);
				checkWellFormedRecursionWalker((Node *) stmt->limitOffset,
											   cstate);
				checkWellFormedRecursionWalker((Node *) stmt->limitCount,
											   cstate);
				checkWellFormedRecursionWalker((Node *) stmt->lockingClause,
											   cstate);
				/* stmt->withClause is intentionally ignored here */
				break;
			default:
				elog(ERROR, "unrecognized set op: %d",
					 (int) stmt->op);
		}
	}
}