Refactor parser's generation of Var nodes.

Instead of passing around a pointer to the RangeTblEntry that
provides the desired column, pass a pointer to the associated
ParseNamespaceItem.  The RTE is trivially reachable from the nsitem,
and having the ParseNamespaceItem allows access to additional
information.  As proof of concept for that, add the rangetable index
to ParseNamespaceItem, and use that to get rid of RTERangeTablePosn
searches.

(I have in mind to teach the parser to generate some different
representation for Vars that are nullable by outer joins, and
keeping the necessary information in ParseNamespaceItems seems
like a reasonable approach to that.  But whether that ever
happens or not, this seems like good cleanup.)

Also refactor the code around scanRTEForColumn so that the
"fuzzy match" stuff does not leak out of parse_relation.c.

Discussion: https://postgr.es/m/26144.1576858373@sss.pgh.pa.us

1 files changed, 15 insertions, 8 deletions

diff --git a/src/backend/parser/parse_clause.c b/src/backend/parser/parse_clause.c
index fe41918f33f..ebbba2d7b5f 100644
--- a/src/backend/parser/parse_clause.c
+++ b/src/backend/parser/parse_clause.c
@@ -52,7 +52,8 @@
 #include "utils/syscache.h"
 
 /* Convenience macro for the most common makeNamespaceItem() case */
-#define makeDefaultNSItem(rte)	makeNamespaceItem(rte, true, true, false, true)
+#define makeDefaultNSItem(rte, rti) \
+	makeNamespaceItem(rte, rti, true, true, false, true)
 
 static void extractRemainingColumns(List *common_colnames,
 									List *src_colnames, List *src_colvars,
@@ -78,7 +79,7 @@ static Node *transformFromClauseItem(ParseState *pstate, Node *n,
 									 List **namespace);
 static Node *buildMergedJoinVar(ParseState *pstate, JoinType jointype,
 								Var *l_colvar, Var *r_colvar);
-static ParseNamespaceItem *makeNamespaceItem(RangeTblEntry *rte,
+static ParseNamespaceItem *makeNamespaceItem(RangeTblEntry *rte, int rtindex,
 											 bool rel_visible, bool cols_visible,
 											 bool lateral_only, bool lateral_ok);
 static void setNamespaceColumnVisibility(List *namespace, bool cols_visible);
@@ -216,12 +217,15 @@ setTargetTable(ParseState *pstate, RangeVar *relation,
 	rte = addRangeTableEntryForRelation(pstate, pstate->p_target_relation,
 										RowExclusiveLock,
 										relation->alias, inh, false);
-	pstate->p_target_rangetblentry = rte;
 
 	/* assume new rte is at end */
 	rtindex = list_length(pstate->p_rtable);
 	Assert(rte == rt_fetch(rtindex, pstate->p_rtable));
 
+	/* remember the RTE as being the query target */
+	pstate->p_target_rangetblentry = rte;
+	pstate->p_target_rtindex = rtindex;
+
 	/*
 	 * Override addRangeTableEntry's default ACL_SELECT permissions check, and
 	 * instead mark target table as requiring exactly the specified
@@ -1084,7 +1088,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		Assert(rte == rt_fetch(rtindex, pstate->p_rtable));
 		*top_rte = rte;
 		*top_rti = rtindex;
-		*namespace = list_make1(makeDefaultNSItem(rte));
+		*namespace = list_make1(makeDefaultNSItem(rte, rtindex));
 		rtr = makeNode(RangeTblRef);
 		rtr->rtindex = rtindex;
 		return (Node *) rtr;
@@ -1102,7 +1106,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		Assert(rte == rt_fetch(rtindex, pstate->p_rtable));
 		*top_rte = rte;
 		*top_rti = rtindex;
-		*namespace = list_make1(makeDefaultNSItem(rte));
+		*namespace = list_make1(makeDefaultNSItem(rte, rtindex));
 		rtr = makeNode(RangeTblRef);
 		rtr->rtindex = rtindex;
 		return (Node *) rtr;
@@ -1120,7 +1124,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		Assert(rte == rt_fetch(rtindex, pstate->p_rtable));
 		*top_rte = rte;
 		*top_rti = rtindex;
-		*namespace = list_make1(makeDefaultNSItem(rte));
+		*namespace = list_make1(makeDefaultNSItem(rte, rtindex));
 		rtr = makeNode(RangeTblRef);
 		rtr->rtindex = rtindex;
 		return (Node *) rtr;
@@ -1138,7 +1142,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		Assert(rte == rt_fetch(rtindex, pstate->p_rtable));
 		*top_rte = rte;
 		*top_rti = rtindex;
-		*namespace = list_make1(makeDefaultNSItem(rte));
+		*namespace = list_make1(makeDefaultNSItem(rte, rtindex));
 		rtr = makeNode(RangeTblRef);
 		rtr->rtindex = rtindex;
 		return (Node *) rtr;
@@ -1481,6 +1485,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		 */
 		*namespace = lappend(my_namespace,
 							 makeNamespaceItem(rte,
+											   j->rtindex,
 											   (j->alias != NULL),
 											   true,
 											   false,
@@ -1617,13 +1622,15 @@ buildMergedJoinVar(ParseState *pstate, JoinType jointype,
  *	  Convenience subroutine to construct a ParseNamespaceItem.
  */
 static ParseNamespaceItem *
-makeNamespaceItem(RangeTblEntry *rte, bool rel_visible, bool cols_visible,
+makeNamespaceItem(RangeTblEntry *rte, int rtindex,
+				  bool rel_visible, bool cols_visible,
 				  bool lateral_only, bool lateral_ok)
 {
 	ParseNamespaceItem *nsitem;
 
 	nsitem = (ParseNamespaceItem *) palloc(sizeof(ParseNamespaceItem));
 	nsitem->p_rte = rte;
+	nsitem->p_rtindex = rtindex;
 	nsitem->p_rel_visible = rel_visible;
 	nsitem->p_cols_visible = cols_visible;
 	nsitem->p_lateral_only = lateral_only;