Split create_foreignscan_path() into three functions.

Up to now postgres_fdw has been using create_foreignscan_path() to
generate not only base-relation paths, but also paths for foreign joins
and foreign upperrels.  This is wrong, because create_foreignscan_path()
calls get_baserel_parampathinfo() which will only do the right thing for
baserels.  It accidentally fails to fail for unparameterized paths, which
are the only ones postgres_fdw (thought it) was handling, but we really
need different APIs for the baserel and join cases.

In HEAD, the best thing to do seems to be to split up the baserel,
joinrel, and upperrel cases into three functions so that they can
have different APIs.  I haven't actually given create_foreign_join_path
a different API in this commit: we should spend a bit of time thinking
about just what we want to do there, since perhaps FDWs would want to
do something different from the build-up-a-join-pairwise approach that
get_joinrel_parampathinfo expects.  In the meantime, since postgres_fdw
isn't prepared to generate parameterized joins anyway, just give it a
defense against trying to plan joins with lateral refs.

In addition (and this is what triggered this whole mess) fix bug #15613
from Srinivasan S A, by teaching file_fdw and postgres_fdw that plain
baserel foreign paths still have outer refs if the relation has
lateral_relids.  Add some assertions in relnode.c to catch future
occurrences of the same error --- in particular, to catch other FDWs
doing that, but also as backstop against core-code mistakes like the
one fixed by commit bdd9a99aa.

Bug #15613 also needs to be fixed in the back branches, but the
appropriate fix will look quite a bit different there, since we don't
want to assume that existing FDWs get the word right away.

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 f438165650c..bab8479cf6a 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -879,6 +879,32 @@ select c2, sum from "S 1"."T 1" t1, lateral (select sum(t2.c1 + t1."C 1") sum fr
 select c2, sum from "S 1"."T 1" t1, lateral (select sum(t2.c1 + t1."C 1") sum from ft2 t2 group by t2.c1) qry where t1.c2 * 2 = qry.sum and t1.c2 < 3 and t1."C 1" < 100 order by 1;
 reset enable_hashagg;
 
+-- 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";
+
 -- Check with placeHolderVars
 explain (verbose, costs off)
 select sum(q.a), count(q.b) from ft4 left join (select 13, avg(ft1.c1), sum(ft2.c1) from ft1 right join ft2 on (ft1.c1 = ft2.c1)) q(a, b, c) on (ft4.c1 <= q.b);