Add p_names field to ParseNamespaceItem

ParseNamespaceItem had a wired-in assumption that p_rte->eref
describes the table and column aliases exposed by the nsitem.  This
relaxes this by creating a separate p_names field in an nsitem.  This
is mainly preparation for a patch for JOIN USING aliases, but it saves
one indirection in common code paths, so it's possibly a win on its
own.

Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/785329.1616455091@sss.pgh.pa.us

src/backend/parser/parse_clause.c

@@ -1217,9 +1217,9 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		 * input column numbers more easily.
 		 */
 		l_nscolumns = l_nsitem->p_nscolumns;
-		l_colnames = l_nsitem->p_rte->eref->colnames;
+		l_colnames = l_nsitem->p_names->colnames;
 		r_nscolumns = r_nsitem->p_nscolumns;
-		r_colnames = r_nsitem->p_rte->eref->colnames;
+		r_colnames = r_nsitem->p_names->colnames;
 
 		/*
 		 * Natural join does not explicitly specify columns; must generate
@@ -1469,7 +1469,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		 * Now that we know the join RTE's rangetable index, we can fix up the
 		 * res_nscolumns data in places where it should contain that.
 		 */
-		Assert(res_colindex == list_length(nsitem->p_rte->eref->colnames));
+		Assert(res_colindex == list_length(nsitem->p_names->colnames));
 		for (k = 0; k < res_colindex; k++)
 		{
 			ParseNamespaceColumn *nscol = res_nscolumns + k;

src/backend/parser/parse_relation.c

@@ -65,6 +65,7 @@ static ParseNamespaceItem *scanNameSpaceForRelid(ParseState *pstate, Oid relid,
 static void check_lateral_ref_ok(ParseState *pstate, ParseNamespaceItem *nsitem,
 								 int location);
 static int	scanRTEForColumn(ParseState *pstate, RangeTblEntry *rte,
+							 Alias *eref,
 							 const char *colname, int location,
 							 int fuzzy_rte_penalty,
 							 FuzzyAttrMatchState *fuzzystate);
@@ -184,7 +185,6 @@ scanNameSpaceForRefname(ParseState *pstate, const char *refname, int location)
 	foreach(l, pstate->p_namespace)
 	{
 		ParseNamespaceItem *nsitem = (ParseNamespaceItem *) lfirst(l);
-		RangeTblEntry *rte = nsitem->p_rte;
 
 		/* Ignore columns-only items */
 		if (!nsitem->p_rel_visible)
@@ -193,7 +193,7 @@ scanNameSpaceForRefname(ParseState *pstate, const char *refname, int location)
 		if (nsitem->p_lateral_only && !pstate->p_lateral_active)
 			continue;
 
-		if (strcmp(rte->eref->aliasname, refname) == 0)
+		if (strcmp(nsitem->p_names->aliasname, refname) == 0)
 		{
 			if (result)
 				ereport(ERROR,
@@ -420,7 +420,7 @@ checkNameSpaceConflicts(ParseState *pstate, List *namespace1,
 	{
 		ParseNamespaceItem *nsitem1 = (ParseNamespaceItem *) lfirst(l1);
 		RangeTblEntry *rte1 = nsitem1->p_rte;
-		const char *aliasname1 = rte1->eref->aliasname;
+		const char *aliasname1 = nsitem1->p_names->aliasname;
 		ListCell   *l2;
 
 		if (!nsitem1->p_rel_visible)
@@ -430,10 +430,11 @@ checkNameSpaceConflicts(ParseState *pstate, List *namespace1,
 		{
 			ParseNamespaceItem *nsitem2 = (ParseNamespaceItem *) lfirst(l2);
 			RangeTblEntry *rte2 = nsitem2->p_rte;
+			const char *aliasname2 = nsitem2->p_names->aliasname;
 
 			if (!nsitem2->p_rel_visible)
 				continue;
-			if (strcmp(rte2->eref->aliasname, aliasname1) != 0)
+			if (strcmp(aliasname2, aliasname1) != 0)
 				continue;		/* definitely no conflict */
 			if (rte1->rtekind == RTE_RELATION && rte1->alias == NULL &&
 				rte2->rtekind == RTE_RELATION && rte2->alias == NULL &&
@@ -466,7 +467,7 @@ check_lateral_ref_ok(ParseState *pstate, ParseNamespaceItem *nsitem,
 	{
 		/* SQL:2008 demands this be an error, not an invisible item */
 		RangeTblEntry *rte = nsitem->p_rte;
-		char	   *refname = rte->eref->aliasname;
+		char	   *refname = nsitem->p_names->aliasname;
 
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
@@ -672,10 +673,10 @@ scanNSItemForColumn(ParseState *pstate, ParseNamespaceItem *nsitem,
 	Var		   *var;
 
 	/*
-	 * Scan the RTE's column names (or aliases) for a match.  Complain if
+	 * Scan the nsitem's column names (or aliases) for a match.  Complain if
 	 * multiple matches.
 	 */
-	attnum = scanRTEForColumn(pstate, rte,
+	attnum = scanRTEForColumn(pstate, rte, nsitem->p_names,
 							  colname, location,
 							  0, NULL);
 
@@ -712,7 +713,7 @@ scanNSItemForColumn(ParseState *pstate, ParseNamespaceItem *nsitem,
 					(errcode(ERRCODE_UNDEFINED_COLUMN),
 					 errmsg("column \"%s\" of relation \"%s\" does not exist",
 							colname,
-							rte->eref->aliasname)));
+							nsitem->p_names->aliasname)));
 
 		var = makeVar(nscol->p_varno,
 					  nscol->p_varattno,
@@ -765,6 +766,7 @@ scanNSItemForColumn(ParseState *pstate, ParseNamespaceItem *nsitem,
  */
 static int
 scanRTEForColumn(ParseState *pstate, RangeTblEntry *rte,
+				 Alias *eref,
 				 const char *colname, int location,
 				 int fuzzy_rte_penalty,
 				 FuzzyAttrMatchState *fuzzystate)
@@ -786,7 +788,7 @@ scanRTEForColumn(ParseState *pstate, RangeTblEntry *rte,
 	 * Callers interested in finding match with shortest distance need to
 	 * defend against this directly, though.
 	 */
-	foreach(c, rte->eref->colnames)
+	foreach(c, eref->colnames)
 	{
 		const char *attcolname = strVal(lfirst(c));
 
@@ -970,7 +972,7 @@ searchRangeTableForCol(ParseState *pstate, const char *alias, const char *colnam
 			 * Scan for a matching column; if we find an exact match, we're
 			 * done.  Otherwise, update fuzzystate.
 			 */
-			if (scanRTEForColumn(orig_pstate, rte, colname, location,
+			if (scanRTEForColumn(orig_pstate, rte, rte->eref, colname, location,
 								 fuzzy_rte_penalty, fuzzystate)
 				&& fuzzy_rte_penalty == 0)
 			{
@@ -1252,6 +1254,7 @@ buildNSItemFromTupleDesc(RangeTblEntry *rte, Index rtindex, TupleDesc tupdesc)
 
 	/* ... and build the nsitem */
 	nsitem = (ParseNamespaceItem *) palloc(sizeof(ParseNamespaceItem));
+	nsitem->p_names = rte->eref;
 	nsitem->p_rte = rte;
 	nsitem->p_rtindex = rtindex;
 	nsitem->p_nscolumns = nscolumns;
@@ -1313,6 +1316,7 @@ buildNSItemFromLists(RangeTblEntry *rte, Index rtindex,
 
 	/* ... and build the nsitem */
 	nsitem = (ParseNamespaceItem *) palloc(sizeof(ParseNamespaceItem));
+	nsitem->p_names = rte->eref;
 	nsitem->p_rte = rte;
 	nsitem->p_rtindex = rtindex;
 	nsitem->p_nscolumns = nscolumns;
@@ -2198,6 +2202,7 @@ addRangeTableEntryForJoin(ParseState *pstate,
 	 * list --- caller must do that if appropriate.
 	 */
 	nsitem = (ParseNamespaceItem *) palloc(sizeof(ParseNamespaceItem));
+	nsitem->p_names = rte->eref;
 	nsitem->p_rte = rte;
 	nsitem->p_rtindex = list_length(pstate->p_rtable);
 	nsitem->p_nscolumns = nscolumns;
@@ -2356,7 +2361,7 @@ addRangeTableEntryForCTE(ParseState *pstate,
 	 */
 	if (rte->ctelevelsup > 0)
 		for (int i = 0; i < n_dontexpand_columns; i++)
-			psi->p_nscolumns[list_length(psi->p_rte->eref->colnames) - 1 - i].p_dontexpand = true;
+			psi->p_nscolumns[list_length(psi->p_names->colnames) - 1 - i].p_dontexpand = true;
 
 	return psi;
 }
@@ -3037,7 +3042,7 @@ expandNSItemVars(ParseNamespaceItem *nsitem,
 	if (colnames)
 		*colnames = NIL;
 	colindex = 0;
-	foreach(lc, nsitem->p_rte->eref->colnames)
+	foreach(lc, nsitem->p_names->colnames)
 	{
 		Value	   *colnameval = (Value *) lfirst(lc);
 		const char *colname = strVal(colnameval);

src/include/parser/parse_node.h

@@ -227,8 +227,13 @@ struct ParseState
 /*
  * An element of a namespace list.
  *
+ * p_names contains the table name and column names exposed by this nsitem.
+ * (Currently, it's always equal to p_rte->eref.)
+ *
+ * p_rte and p_rtindex link to the underlying rangetable entry.
+ *
  * The p_nscolumns array contains info showing how to construct Vars
- * referencing corresponding elements of the RTE's colnames list.
+ * referencing the names appearing in the p_names->colnames list.
  *
  * Namespace items with p_rel_visible set define which RTEs are accessible by
  * qualified names, while those with p_cols_visible set define which RTEs are
@@ -256,9 +261,10 @@ struct ParseState
  */
 struct ParseNamespaceItem
 {
+	Alias	   *p_names;		/* Table and column names */
 	RangeTblEntry *p_rte;		/* The relation's rangetable entry */
 	int			p_rtindex;		/* The relation's index in the rangetable */
-	/* array of same length as p_rte->eref->colnames: */
+	/* array of same length as p_names->colnames: */
 	ParseNamespaceColumn *p_nscolumns;	/* per-column data */
 	bool		p_rel_visible;	/* Relation name is visible? */
 	bool		p_cols_visible; /* Column names visible as unqualified refs? */