Fix miscomputation of direct_lateral_relids for join relations.

If a PlaceHolderVar is to be evaluated at a join relation, but
its value is only needed there and not at higher levels, we neglected
to update the joinrel's direct_lateral_relids to include the PHV's
source rel.  This causes problems because join_is_legal() then won't
allow joining the joinrel to the PHV's source rel at all, leading
to "failed to build any N-way joins" planner failures.

Per report from Andreas Seltenreich.  Back-patch to 9.5
where the problem originated.

Discussion: https://postgr.es/m/87blfgqa4t.fsf@aurora.ydns.eu

1 files changed, 64 insertions, 0 deletions

diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index 60b621b651..a118041731 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -3011,6 +3011,70 @@ order by 1,2;
 (8 rows)
 
 --
+-- variant where a PlaceHolderVar is needed at a join, but not above the join
+--
+explain (costs off)
+select * from
+  int4_tbl as i41,
+  lateral
+    (select 1 as x from
+      (select i41.f1 as lat,
+              i42.f1 as loc from
+         int8_tbl as i81, int4_tbl as i42) as ss1
+      right join int4_tbl as i43 on (i43.f1 > 1)
+      where ss1.loc = ss1.lat) as ss2
+where i41.f1 > 0;
+                    QUERY PLAN                    
+--------------------------------------------------
+ Nested Loop
+   ->  Nested Loop
+         ->  Seq Scan on int4_tbl i41
+               Filter: (f1 > 0)
+         ->  Nested Loop
+               Join Filter: (i41.f1 = i42.f1)
+               ->  Seq Scan on int8_tbl i81
+               ->  Materialize
+                     ->  Seq Scan on int4_tbl i42
+   ->  Materialize
+         ->  Seq Scan on int4_tbl i43
+               Filter: (f1 > 1)
+(12 rows)
+
+select * from
+  int4_tbl as i41,
+  lateral
+    (select 1 as x from
+      (select i41.f1 as lat,
+              i42.f1 as loc from
+         int8_tbl as i81, int4_tbl as i42) as ss1
+      right join int4_tbl as i43 on (i43.f1 > 1)
+      where ss1.loc = ss1.lat) as ss2
+where i41.f1 > 0;
+     f1     | x 
+------------+---
+     123456 | 1
+     123456 | 1
+     123456 | 1
+     123456 | 1
+     123456 | 1
+     123456 | 1
+     123456 | 1
+     123456 | 1
+     123456 | 1
+     123456 | 1
+ 2147483647 | 1
+ 2147483647 | 1
+ 2147483647 | 1
+ 2147483647 | 1
+ 2147483647 | 1
+ 2147483647 | 1
+ 2147483647 | 1
+ 2147483647 | 1
+ 2147483647 | 1
+ 2147483647 | 1
+(20 rows)
+
+--
 -- test the corner cases FULL JOIN ON TRUE and FULL JOIN ON FALSE
 --
 select * from int4_tbl a full join int4_tbl b on true;