Add minimal regression test for blessed record type transfer.

Test that blessed records can be transferred through a TupleQueue and
correctly decoded by another backend.  While touching the file, make
sure that force_parallel_mode settings only cover relevant tests.

Author: Thomas Munro, editorialized by Andres Freund
Reviewed-By: Andres Freund
Discussion: https://postgr.es/m/20170823054644.efuzftxjpfi6wwqs%40alap3.anarazel.de

src/test/regress/expected/select_parallel.out

@@ -326,7 +326,8 @@ select string4 from tenk1 order by string4 limit 5;
 
 reset max_parallel_workers;
 reset enable_hashagg;
-set force_parallel_mode=1;
+SAVEPOINT settings;
+SET LOCAL force_parallel_mode = 1;
 explain (costs off)
   select stringu1::int2 from tenk1 where unique1 = 1;
                   QUERY PLAN                   
@@ -338,7 +339,38 @@ explain (costs off)
          Index Cond: (unique1 = 1)
 (5 rows)
 
+ROLLBACK TO SAVEPOINT settings;
+-- exercise record typmod remapping between backends
+CREATE OR REPLACE FUNCTION make_record(n int)
+  RETURNS RECORD LANGUAGE plpgsql PARALLEL SAFE AS
+$$
+BEGIN
+  RETURN CASE n
+           WHEN 1 THEN ROW(1)
+           WHEN 2 THEN ROW(1, 2)
+           WHEN 3 THEN ROW(1, 2, 3)
+           WHEN 4 THEN ROW(1, 2, 3, 4)
+           ELSE ROW(1, 2, 3, 4, 5)
+         END;
+END;
+$$;
+SAVEPOINT settings;
+SET LOCAL force_parallel_mode = 1;
+SELECT make_record(x) FROM (SELECT generate_series(1, 5) x) ss ORDER BY x;
+ make_record 
+-------------
+ (1)
+ (1,2)
+ (1,2,3)
+ (1,2,3,4)
+ (1,2,3,4,5)
+(5 rows)
+
+ROLLBACK TO SAVEPOINT settings;
+DROP function make_record(n int);
 -- to increase the parallel query test coverage
+SAVEPOINT settings;
+SET LOCAL force_parallel_mode = 1;
 EXPLAIN (analyze, timing off, summary off, costs off) SELECT * FROM tenk1;
                          QUERY PLAN                          
 -------------------------------------------------------------
@@ -348,8 +380,12 @@ EXPLAIN (analyze, timing off, summary off, costs off) SELECT * FROM tenk1;
    ->  Parallel Seq Scan on tenk1 (actual rows=2000 loops=5)
 (4 rows)
 
+ROLLBACK TO SAVEPOINT settings;
 -- provoke error in worker
+SAVEPOINT settings;
+SET LOCAL force_parallel_mode = 1;
 select stringu1::int2 from tenk1 where unique1 = 1;
 ERROR:  invalid input syntax for integer: "BAAAAA"
 CONTEXT:  parallel worker
+ROLLBACK TO SAVEPOINT settings;
 rollback;

src/test/regress/sql/select_parallel.sql

@@ -126,15 +126,42 @@ select string4 from tenk1 order by string4 limit 5;
 reset max_parallel_workers;
 reset enable_hashagg;
 
-set force_parallel_mode=1;
-
+SAVEPOINT settings;
+SET LOCAL force_parallel_mode = 1;
 explain (costs off)
   select stringu1::int2 from tenk1 where unique1 = 1;
+ROLLBACK TO SAVEPOINT settings;
+
+-- exercise record typmod remapping between backends
+CREATE OR REPLACE FUNCTION make_record(n int)
+  RETURNS RECORD LANGUAGE plpgsql PARALLEL SAFE AS
+$$
+BEGIN
+  RETURN CASE n
+           WHEN 1 THEN ROW(1)
+           WHEN 2 THEN ROW(1, 2)
+           WHEN 3 THEN ROW(1, 2, 3)
+           WHEN 4 THEN ROW(1, 2, 3, 4)
+           ELSE ROW(1, 2, 3, 4, 5)
+         END;
+END;
+$$;
+SAVEPOINT settings;
+SET LOCAL force_parallel_mode = 1;
+SELECT make_record(x) FROM (SELECT generate_series(1, 5) x) ss ORDER BY x;
+ROLLBACK TO SAVEPOINT settings;
+DROP function make_record(n int);
 
 -- to increase the parallel query test coverage
+SAVEPOINT settings;
+SET LOCAL force_parallel_mode = 1;
 EXPLAIN (analyze, timing off, summary off, costs off) SELECT * FROM tenk1;
+ROLLBACK TO SAVEPOINT settings;
 
 -- provoke error in worker
+SAVEPOINT settings;
+SET LOCAL force_parallel_mode = 1;
 select stringu1::int2 from tenk1 where unique1 = 1;
+ROLLBACK TO SAVEPOINT settings;
 
 rollback;