Fix pull_varnos to cope with translated PlaceHolderVars.

Commit 55dc86eca changed pull_varnos to use (if possible) the associated
ph_eval_at for a PlaceHolderVar.  I missed a fine point though: we might
be looking at a PHV in the quals or tlist of a child appendrel, in which
case we need to compute a ph_eval_at value that's been translated in the
same way that the PHV itself has been (cf. adjust_appendrel_attrs).
Fortunately, enough info is available in the PlaceHolderInfo to make
such translation possible without additional outside data, so we don't
need another round of uglification of planner APIs.  This is a little
bit complicated, but since it's a hard-to-hit corner case, I'm not much
worried about adding cycles here.

Per report from Jaime Casanova.  Back-patch to v12, like the previous
commit.

Discussion: https://postgr.es/m/20210915230959.GB17635@ahch-to

1 files changed, 38 insertions, 3 deletions

diff --git a/src/backend/optimizer/util/var.c b/src/backend/optimizer/util/var.c
index e307d6fbb07..e57c3aa1244 100644
--- a/src/backend/optimizer/util/var.c
+++ b/src/backend/optimizer/util/var.c
@@ -188,6 +188,16 @@ pull_varnos_walker(Node *node, pull_varnos_context *context)
 			 * join that forces delay of evaluation of a given qual clause
 			 * will be processed before we examine that clause here, so the
 			 * ph_eval_at value should have been updated to include it.
+			 *
+			 * Another problem is that a PlaceHolderVar can appear in quals or
+			 * tlists that have been translated for use in a child appendrel.
+			 * Typically such a PHV is a parameter expression sourced by some
+			 * other relation, so that the translation from parent appendrel
+			 * to child doesn't change its phrels, and we should still take
+			 * ph_eval_at at face value.  But in corner cases, the PHV's
+			 * original phrels can include the parent appendrel itself, in
+			 * which case the translated PHV will have the child appendrel in
+			 * phrels, and we must translate ph_eval_at to match.
 			 */
 			PlaceHolderInfo *phinfo = NULL;
 
@@ -203,12 +213,37 @@ pull_varnos_walker(Node *node, pull_varnos_context *context)
 					phinfo = NULL;
 				}
 			}
-			if (phinfo != NULL)
+			if (phinfo == NULL)
+			{
+				/* No PlaceHolderInfo yet, use phrels */
+				context->varnos = bms_add_members(context->varnos,
+												  phv->phrels);
+			}
+			else if (bms_equal(phv->phrels, phinfo->ph_var->phrels))
+			{
+				/* Normal case: use ph_eval_at */
 				context->varnos = bms_add_members(context->varnos,
 												  phinfo->ph_eval_at);
+			}
 			else
-				context->varnos = bms_add_members(context->varnos,
-												  phv->phrels);
+			{
+				/* Translated PlaceHolderVar: translate ph_eval_at to match */
+				Relids		newevalat,
+							delta;
+
+				/* remove what was removed from phv->phrels ... */
+				delta = bms_difference(phinfo->ph_var->phrels, phv->phrels);
+				newevalat = bms_difference(phinfo->ph_eval_at, delta);
+				/* ... then if that was in fact part of ph_eval_at ... */
+				if (!bms_equal(newevalat, phinfo->ph_eval_at))
+				{
+					/* ... add what was added */
+					delta = bms_difference(phv->phrels, phinfo->ph_var->phrels);
+					newevalat = bms_join(newevalat, delta);
+				}
+				context->varnos = bms_join(context->varnos,
+										   newevalat);
+			}
 			return false;		/* don't recurse into expression */
 		}
 	}