Ensure that foreign scans with lateral refs are planned correctly.

As reported in bug #15613 from Srinivasan S A, file_fdw and postgres_fdw
neglected to mark plain baserel foreign paths as parameterized when the
relation has lateral_relids.  Other FDWs have surely copied this mistake,
so rather than just patching those two modules, install a band-aid fix
in create_foreignscan_path to rectify the mistake centrally.

Although the band-aid is enough to fix the visible symptom, correct
the calls in file_fdw and postgres_fdw anyway, so that they are valid
examples for external FDWs.

Also, since the band-aid isn't enough to make this work for parameterized
foreign joins, throw an elog(ERROR) if such a case is passed to
create_foreignscan_path.  This shouldn't pose much of a problem for
existing external FDWs, since it's likely they aren't trying to make such
paths anyway (though some of them may need a defense against joins with
lateral_relids, similar to the one this patch installs into postgres_fdw).

Add some assertions in relnode.c to catch future occurrences of the same
error --- in particular, as backstop against core-code mistakes like the
one fixed by commit bdd9a99aa.

Discussion: https://postgr.es/m/15613-092be1be9576c728@postgresql.org

1 files changed, 26 insertions, 0 deletions

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 698be8e2917..a439239bff6 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -238,6 +238,32 @@ WHERE a.c2 = 6 AND b.c1 = a.c1 AND a.c8 = 'foo' AND b.c7 = upper(a.c7);
 SELECT * FROM ft1 WHERE c1 = ANY (ARRAY(SELECT c1 FROM ft2 WHERE c1 < 5));
 SELECT * FROM ft2 WHERE c1 = ANY (ARRAY(SELECT c1 FROM ft1 WHERE c1 < 5));
 
+-- bug #15613: bad plan for foreign table scan with lateral reference
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT ref_0.c2, subq_1.*
+FROM
+    "S 1"."T 1" AS ref_0,
+    LATERAL (
+        SELECT ref_0."C 1" c1, subq_0.*
+        FROM (SELECT ref_0.c2, ref_1.c3
+              FROM ft1 AS ref_1) AS subq_0
+             RIGHT JOIN ft2 AS ref_3 ON (subq_0.c3 = ref_3.c3)
+    ) AS subq_1
+WHERE ref_0."C 1" < 10 AND subq_1.c3 = '00001'
+ORDER BY ref_0."C 1";
+
+SELECT ref_0.c2, subq_1.*
+FROM
+    "S 1"."T 1" AS ref_0,
+    LATERAL (
+        SELECT ref_0."C 1" c1, subq_0.*
+        FROM (SELECT ref_0.c2, ref_1.c3
+              FROM ft1 AS ref_1) AS subq_0
+             RIGHT JOIN ft2 AS ref_3 ON (subq_0.c3 = ref_3.c3)
+    ) AS subq_1
+WHERE ref_0."C 1" < 10 AND subq_1.c3 = '00001'
+ORDER BY ref_0."C 1";
+
 -- ===================================================================
 -- parameterized queries
 -- ===================================================================