Fix setrefs.c's failure to do expression processing on prune steps.

We should run the expression subtrees of PartitionedRelPruneInfo
structs through fix_scan_expr.  Failure to do so means that
AlternativeSubPlans within those expressions won't be cleaned up
properly, resulting in "unrecognized node type" errors since v14.

It seems fairly likely that at least some of the other steps done
by fix_scan_expr are important here as well, resulting in as-yet-
undetected bugs.  Therefore, I've chosen to back-patch this to
all supported branches including v13, even though the known
symptom doesn't manifest in v13.

Per bug #18778 from Alexander Lakhin.

Discussion: https://postgr.es/m/18778-24cd399df6c806af@postgresql.org

src/backend/optimizer/plan/setrefs.c

@@ -1795,6 +1795,12 @@ set_append_references(PlannerInfo *root,
 				PartitionedRelPruneInfo *pinfo = lfirst(l2);
 
 				pinfo->rtindex += rtoffset;
+				pinfo->initial_pruning_steps =
+					fix_scan_list(root, pinfo->initial_pruning_steps,
+								  rtoffset, 1);
+				pinfo->exec_pruning_steps =
+					fix_scan_list(root, pinfo->exec_pruning_steps,
+								  rtoffset, 1);
 			}
 		}
 	}
@@ -1871,6 +1877,12 @@ set_mergeappend_references(PlannerInfo *root,
 				PartitionedRelPruneInfo *pinfo = lfirst(l2);
 
 				pinfo->rtindex += rtoffset;
+				pinfo->initial_pruning_steps =
+					fix_scan_list(root, pinfo->initial_pruning_steps,
+								  rtoffset, 1);
+				pinfo->exec_pruning_steps =
+					fix_scan_list(root, pinfo->exec_pruning_steps,
+								  rtoffset, 1);
 			}
 		}
 	}

src/test/regress/expected/partition_prune.out

@@ -1893,6 +1893,35 @@ explain (costs off) select * from rparted_by_int2 where a > 100_000_000_000_000;
 (2 rows)
 
 drop table lp, coll_pruning, rlp, mc3p, mc2p, boolpart, iboolpart, boolrangep, rp, coll_pruning_multi, like_op_noprune, lparted_by_int2, rparted_by_int2;
+-- check that AlternativeSubPlan within a pruning expression gets cleaned up
+create table asptab (id int primary key) partition by range (id);
+create table asptab0 partition of asptab for values from (0) to (1);
+create table asptab1 partition of asptab for values from (1) to (2);
+explain (costs off)
+select * from
+  (select exists (select 1 from int4_tbl tinner where f1 = touter.f1) as b
+   from int4_tbl touter) ss,
+  asptab
+where asptab.id > ss.b::int;
+                             QUERY PLAN                             
+--------------------------------------------------------------------
+ Nested Loop
+   ->  Seq Scan on int4_tbl touter
+   ->  Append
+         ->  Index Only Scan using asptab0_pkey on asptab0 asptab_1
+               Index Cond: (id > (EXISTS(SubPlan 3))::integer)
+               SubPlan 4
+                 ->  Seq Scan on int4_tbl tinner_2
+         ->  Index Only Scan using asptab1_pkey on asptab1 asptab_2
+               Index Cond: (id > (EXISTS(SubPlan 3))::integer)
+         SubPlan 3
+           ->  Seq Scan on int4_tbl tinner_1
+                 Filter: (f1 = touter.f1)
+   SubPlan 2
+     ->  Seq Scan on int4_tbl tinner
+(14 rows)
+
+drop table asptab;
 --
 -- Test Partition pruning for HASH partitioning
 --

src/test/regress/sql/partition_prune.sql

@@ -388,6 +388,21 @@ explain (costs off) select * from rparted_by_int2 where a > 100_000_000_000_000;
 
 drop table lp, coll_pruning, rlp, mc3p, mc2p, boolpart, iboolpart, boolrangep, rp, coll_pruning_multi, like_op_noprune, lparted_by_int2, rparted_by_int2;
 
+-- check that AlternativeSubPlan within a pruning expression gets cleaned up
+
+create table asptab (id int primary key) partition by range (id);
+create table asptab0 partition of asptab for values from (0) to (1);
+create table asptab1 partition of asptab for values from (1) to (2);
+
+explain (costs off)
+select * from
+  (select exists (select 1 from int4_tbl tinner where f1 = touter.f1) as b
+   from int4_tbl touter) ss,
+  asptab
+where asptab.id > ss.b::int;
+
+drop table asptab;
+
 --
 -- Test Partition pruning for HASH partitioning
 --