Add proper regression test for the recent SRFs-in-pathkeys problem.

Remove the test case added by commit fac1b47, which never actually
worked to expose the problem it claimed to test.  Replace it with
a case that does expose the problem, and also covers the SRF-not-
at-the-top deficiency repaired in 1aa8dad.

Richard Guo, with some editorialization by me

Discussion: https://postgr.es/m/17564-c7472c2f90ef2da3@postgresql.org

Author: tglsfdc

src/test/regress/expected/incremental_sort.out

@@ -1804,15 +1804,3 @@ order by 1, 2;
                ->  Function Scan on generate_series
 (7 rows)
 
--- Disallow pushing down sort when pathkey is an SRF.
-explain (costs off) select unique1 from tenk1 order by unnest('{1,2}'::int[]);
-                               QUERY PLAN                                
--------------------------------------------------------------------------
- Gather Motion 3:1  (slice1; segments: 3)
-   Merge Key: (unnest('{1,2}'::anyarray))
-   ->  Sort
-         Sort Key: (unnest('{1,2}'::anyarray))
-         ->  ProjectSet
-               ->  Index Only Scan using tenk1_unique1 on tenk1
-(6 rows)
-

src/test/regress/expected/incremental_sort_optimizer.out

@@ -1658,17 +1658,3 @@ order by 1, 2;
  Optimizer: Postgres query optimizer
 (8 rows)
 
--- Disallow pushing down sort when pathkey is an SRF.
-explain (costs off) select unique1 from tenk1 order by unnest('{1,2}'::int[]);
-                     QUERY PLAN
------------------------------------------------------
- Result
-   ->  Gather Motion 3:1  (slice1; segments: 3)
-         Merge Key: (unnest('{1,2}'::anyarray))
-         ->  Sort
-               Sort Key: (unnest('{1,2}'::anyarray))
-               ->  ProjectSet
-                     ->  Seq Scan on tenk1
- Optimizer: Pivotal Optimizer (GPORCA)
-(8 rows)
-

src/test/regress/expected/select_parallel.out

@@ -1217,6 +1217,33 @@ SELECT generate_series(1, two), array(select generate_series(1, two))
  Optimizer: Postgres query optimizer
 (18 rows)
 
+-- must disallow pushing sort below gather when pathkey contains an SRF
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT unnest(ARRAY[]::integer[]) + 1 AS pathkey
+  FROM tenk1 t1 JOIN tenk1 t2 ON TRUE
+  ORDER BY pathkey;
+                                                                                                          QUERY PLAN                                                                                                           
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Gather Motion 6:1  (slice1; segments: 6)
+   Output: (((unnest('{}'::integer[])) + 1))
+   Merge Key: (((unnest('{}'::integer[])) + 1))
+   ->  Sort
+         Output: (((unnest('{}'::integer[])) + 1))
+         Sort Key: (((unnest('{}'::integer[])) + 1))
+         ->  Result
+               Output: ((unnest('{}'::integer[])) + 1)
+               ->  ProjectSet
+                     Output: unnest('{}'::integer[])
+                     ->  Nested Loop
+                           ->  Parallel Seq Scan on public.tenk1 t1
+                                 Output: t1.unique1, t1.unique2, t1.two, t1.four, t1.ten, t1.twenty, t1.hundred, t1.thousand, t1.twothousand, t1.fivethous, t1.tenthous, t1.odd, t1.even, t1.stringu1, t1.stringu2, t1.string4
+                           ->  Materialize
+                                 ->  Broadcast Motion 3:6  (slice2; segments: 3)
+                                       ->  Seq Scan on public.tenk1 t2
+ Settings: enable_parallel = 'on', min_parallel_table_scan_size = '0', optimizer = 'off', parallel_setup_cost = '0', parallel_tuple_cost = '0'
+ Optimizer: Postgres query optimizer
+(18 rows)
+
 -- test passing expanded-value representations to workers
 CREATE FUNCTION make_some_array(int,int) returns int[] as
 $$declare x int[];

src/test/regress/sql/incremental_sort.sql

@@ -294,5 +294,3 @@ from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub;
 explain (costs off) select sub.unique1, stringu1 || random()::text
 from tenk1, lateral (select tenk1.unique1 from generate_series(1, 1000)) as sub
 order by 1, 2;
--- Disallow pushing down sort when pathkey is an SRF.
-explain (costs off) select unique1 from tenk1 order by unnest('{1,2}'::int[]);

src/test/regress/sql/select_parallel.sql

@@ -443,6 +443,12 @@ EXPLAIN (VERBOSE, COSTS OFF)
 SELECT generate_series(1, two), array(select generate_series(1, two))
   FROM tenk1 ORDER BY tenthous;
 
+-- must disallow pushing sort below gather when pathkey contains an SRF
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT unnest(ARRAY[]::integer[]) + 1 AS pathkey
+  FROM tenk1 t1 JOIN tenk1 t2 ON TRUE
+  ORDER BY pathkey;
+
 -- test passing expanded-value representations to workers
 CREATE FUNCTION make_some_array(int,int) returns int[] as
 $$declare x int[];