postgres_fdw: Fix join push down with extensions

Objects in an extension are shippable to a foreign server if the
extension is part of the foreign server definition's shippable
extensions list.  But this was not properly considered in some cases
when checking whether a join condition can be pushed to a foreign server
and the join condition uses an object from a shippable extension.  So
the join would never be pushed down in those cases.

So, the list of extensions needs to be made available in fpinfo of the
relation being considered to be pushed down before any expressions are
assessed for being shippable.  Fix foreign_join_ok() to do that for a
join relation.

The code to save FDW options in fpinfo is scattered at multiple places.
Bring all of that together into functions apply_server_options(),
apply_table_options(), and merge_fdw_options().

David Rowley and Ashutosh Bapat, per report from David Rowley

1 files changed, 29 insertions, 0 deletions

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index b29549a28f1..d1bc5b06603 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -1620,6 +1620,35 @@ SELECT t1.c1, t2.c1 FROM ft4 t1 FULL JOIN ft5 t2 ON (t1.c1 = t2.c1) WHERE (t1.c1
     | 21
 (10 rows)
 
+-- full outer join + WHERE clause with shippable extensions set
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1, t2.c2, t1.c3 FROM ft1 t1 FULL JOIN ft2 t2 ON (t1.c1 = t2.c1) WHERE postgres_fdw_abs(t1.c1) > 0 OFFSET 10 LIMIT 10;
+                                                                                  QUERY PLAN                                                                                   
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Limit
+   Output: t1.c1, t2.c2, t1.c3
+   ->  Foreign Scan
+         Output: t1.c1, t2.c2, t1.c3
+         Relations: (public.ft1 t1) FULL JOIN (public.ft2 t2)
+         Remote SQL: SELECT r1."C 1", r1.c3, r2.c2 FROM ("S 1"."T 1" r1 FULL JOIN "S 1"."T 1" r2 ON (((r1."C 1" = r2."C 1")))) WHERE ((public.postgres_fdw_abs(r1."C 1") > 0))
+(6 rows)
+
+ALTER SERVER loopback OPTIONS (DROP extensions);
+-- full outer join + WHERE clause with shippable extensions not set
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT t1.c1, t2.c2, t1.c3 FROM ft1 t1 FULL JOIN ft2 t2 ON (t1.c1 = t2.c1) WHERE postgres_fdw_abs(t1.c1) > 0 OFFSET 10 LIMIT 10;
+                                                          QUERY PLAN                                                           
+-------------------------------------------------------------------------------------------------------------------------------
+ Limit
+   Output: t1.c1, t2.c2, t1.c3
+   ->  Foreign Scan
+         Output: t1.c1, t2.c2, t1.c3
+         Filter: (postgres_fdw_abs(t1.c1) > 0)
+         Relations: (public.ft1 t1) FULL JOIN (public.ft2 t2)
+         Remote SQL: SELECT r1."C 1", r1.c3, r2.c2 FROM ("S 1"."T 1" r1 FULL JOIN "S 1"."T 1" r2 ON (((r1."C 1" = r2."C 1"))))
+(7 rows)
+
+ALTER SERVER loopback OPTIONS (ADD extensions 'postgres_fdw');
 -- join two tables with FOR UPDATE clause
 -- tests whole-row reference for row marks
 EXPLAIN (VERBOSE, COSTS OFF)