Fix planner problems with LATERAL references in PlaceHolderVars.

The planner largely failed to consider the possibility that a
PlaceHolderVar's expression might contain a lateral reference to a Var
coming from somewhere outside the PHV's syntactic scope.  We had a previous
report of a problem in this area, which I tried to fix in a quick-hack way
in commit 4da6439bd8553059766011e2a42c6e39df08717f, but Antonin Houska
pointed out that there were still some problems, and investigation turned
up other issues.  This patch largely reverts that commit in favor of a more
thoroughly thought-through solution.  The new theory is that a PHV's
ph_eval_at level cannot be higher than its original syntactic level.  If it
contains lateral references, those don't change the ph_eval_at level, but
rather they create a lateral-reference requirement for the ph_eval_at join
relation.  The code in joinpath.c needs to handle that.

Another issue is that createplan.c wasn't handling nested PlaceHolderVars
properly.

In passing, push knowledge of lateral-reference checks for join clauses
into join_clause_is_movable_to.  This is mainly so that FDWs don't need
to deal with it.

This patch doesn't fix the original join-qual-placement problem reported by
Jeremy Evans (and indeed, one of the new regression test cases shows the
wrong answer because of that).  But the PlaceHolderVar problems need to be
fixed before that issue can be addressed, so committing this separately
seems reasonable.

1 files changed, 3 insertions, 28 deletions

diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 1c93e0c5ac3..8713eabc646 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -540,7 +540,6 @@ postgresGetForeignPaths(PlannerInfo *root,
 {
 	PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) baserel->fdw_private;
 	ForeignPath *path;
-	Relids		lateral_referencers;
 	List	   *join_quals;
 	Relids		required_outer;
 	double		rows;
@@ -579,34 +578,13 @@ postgresGetForeignPaths(PlannerInfo *root,
 	 * consider combinations of clauses, probably.
 	 */
 
-	/*
-	 * If there are any rels that have LATERAL references to this one, we
-	 * cannot use join quals referencing them as remote quals for this one,
-	 * since such rels would have to be on the inside not the outside of a
-	 * nestloop join relative to this one.	Create a Relids set listing all
-	 * such rels, for use in checks of potential join clauses.
-	 */
-	lateral_referencers = NULL;
-	foreach(lc, root->lateral_info_list)
-	{
-		LateralJoinInfo *ljinfo = (LateralJoinInfo *) lfirst(lc);
-
-		if (bms_is_member(baserel->relid, ljinfo->lateral_lhs))
-			lateral_referencers = bms_add_member(lateral_referencers,
-												 ljinfo->lateral_rhs);
-	}
-
 	/* Scan the rel's join clauses */
 	foreach(lc, baserel->joininfo)
 	{
 		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
 
 		/* Check if clause can be moved to this rel */
-		if (!join_clause_is_movable_to(rinfo, baserel->relid))
-			continue;
-
-		/* Not useful if it conflicts with any LATERAL references */
-		if (bms_overlap(rinfo->clause_relids, lateral_referencers))
+		if (!join_clause_is_movable_to(rinfo, baserel))
 			continue;
 
 		/* See if it is safe to send to remote */
@@ -667,7 +645,7 @@ postgresGetForeignPaths(PlannerInfo *root,
 															 baserel,
 												   ec_member_matches_foreign,
 															 (void *) &arg,
-														lateral_referencers);
+											   baserel->lateral_referencers);
 
 			/* Done if there are no more expressions in the foreign rel */
 			if (arg.current == NULL)
@@ -682,12 +660,9 @@ postgresGetForeignPaths(PlannerInfo *root,
 				RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
 
 				/* Check if clause can be moved to this rel */
-				if (!join_clause_is_movable_to(rinfo, baserel->relid))
+				if (!join_clause_is_movable_to(rinfo, baserel))
 					continue;
 
-				/* Shouldn't conflict with any LATERAL references */
-				Assert(!bms_overlap(rinfo->clause_relids, lateral_referencers));
-
 				/* See if it is safe to send to remote */
 				if (!is_foreign_expr(root, baserel, rinfo->clause))
 					continue;