Copy partitioned_rels lists to avoid shared substructure.

Otherwise, set_plan_refs() can get applied to the same list
multiple times through different references, leading to chaos.

Amit Langote, Dilip Kumar, and Robert Haas, reviewed by Ashutosh
Bapat.  Original report by Sveinn Sveinsson.

Discussion: http://postgr.es/m/20170517141151.1435.79890@wrigleys.postgresql.org

src/backend/optimizer/util/pathnode.c

@@ -1216,7 +1216,7 @@ create_append_path(RelOptInfo *rel, List *subpaths, Relids required_outer,
 	pathnode->path.parallel_workers = parallel_workers;
 	pathnode->path.pathkeys = NIL;		/* result is always considered
 										 * unsorted */
-	pathnode->partitioned_rels = partitioned_rels;
+	pathnode->partitioned_rels = list_copy(partitioned_rels);
 	pathnode->subpaths = subpaths;
 
 	/*
@@ -1276,7 +1276,7 @@ create_merge_append_path(PlannerInfo *root,
 	pathnode->path.parallel_safe = rel->consider_parallel;
 	pathnode->path.parallel_workers = 0;
 	pathnode->path.pathkeys = pathkeys;
-	pathnode->partitioned_rels = partitioned_rels;
+	pathnode->partitioned_rels = list_copy(partitioned_rels);
 	pathnode->subpaths = subpaths;
 
 	/*
@@ -3238,7 +3238,7 @@ create_modifytable_path(PlannerInfo *root, RelOptInfo *rel,
 	pathnode->operation = operation;
 	pathnode->canSetTag = canSetTag;
 	pathnode->nominalRelation = nominalRelation;
-	pathnode->partitioned_rels = partitioned_rels;
+	pathnode->partitioned_rels = list_copy(partitioned_rels);
 	pathnode->resultRelations = resultRelations;
 	pathnode->subpaths = subpaths;
 	pathnode->subroots = subroots;

src/test/regress/expected/inherit.out

@@ -1918,3 +1918,34 @@ explain (costs off) select * from mcrparted where a = 20 and c > 20; -- scans mc
 (7 rows)
 
 drop table mcrparted;
+-- check that partitioned table Appends cope with being referenced in
+-- subplans
+create table parted_minmax (a int, b varchar(16)) partition by range (a);
+create table parted_minmax1 partition of parted_minmax for values from (1) to (10);
+create index parted_minmax1i on parted_minmax1 (a, b);
+insert into parted_minmax values (1,'12345');
+explain (costs off) select min(a), max(a) from parted_minmax where b = '12345';
+                                              QUERY PLAN                                               
+-------------------------------------------------------------------------------------------------------
+ Result
+   InitPlan 1 (returns $0)
+     ->  Limit
+           ->  Merge Append
+                 Sort Key: parted_minmax1.a
+                 ->  Index Only Scan using parted_minmax1i on parted_minmax1
+                       Index Cond: ((a IS NOT NULL) AND (b = '12345'::text))
+   InitPlan 2 (returns $1)
+     ->  Limit
+           ->  Merge Append
+                 Sort Key: parted_minmax1_1.a DESC
+                 ->  Index Only Scan Backward using parted_minmax1i on parted_minmax1 parted_minmax1_1
+                       Index Cond: ((a IS NOT NULL) AND (b = '12345'::text))
+(13 rows)
+
+select min(a), max(a) from parted_minmax where b = '12345';
+ min | max 
+-----+-----
+   1 |   1
+(1 row)
+
+drop table parted_minmax;

src/test/regress/sql/inherit.sql

@@ -661,3 +661,13 @@ explain (costs off) select * from mcrparted where a > -1;	-- scans all partition
 explain (costs off) select * from mcrparted where a = 20 and abs(b) = 10 and c > 10;	-- scans mcrparted4
 explain (costs off) select * from mcrparted where a = 20 and c > 20; -- scans mcrparted3, mcrparte4, mcrparte5
 drop table mcrparted;
+
+-- check that partitioned table Appends cope with being referenced in
+-- subplans
+create table parted_minmax (a int, b varchar(16)) partition by range (a);
+create table parted_minmax1 partition of parted_minmax for values from (1) to (10);
+create index parted_minmax1i on parted_minmax1 (a, b);
+insert into parted_minmax values (1,'12345');
+explain (costs off) select min(a), max(a) from parted_minmax where b = '12345';
+select min(a), max(a) from parted_minmax where b = '12345';
+drop table parted_minmax;