Re: postgres_fdw: wrong results with self join + enable_nestloop off

I think we should choose the latter, so I modified your patch as
mentioned, after re-creating it on top of my patch.  Attached is a new
version (0002-Allow-join-pushdown-even-if-pseudoconstant-quals-v2.patch).
I am attaching my patch as well
(0001-Disable-join-pushdown-if-pseudoconstant-quals-v2.patch).

Other changes made to your patch:

* I renamed the new member of the ForeignPath struct to
fdw_restrictinfo.  (And I named that of the CustomPath struct
custom_restrictinfo.)

* In your patch, only for create_foreign_join_path(), the API was
modified so that the caller provides the new member of ForeignPath,
but I modified that for
create_foreignscan_path()/create_foreign_upper_path() as well, for
consistency.

* In this bit I changed the last argument to NIL, which would be
nitpicking, though.

@@ -1038,7 +1038,7 @@ postgresGetForeignPaths(PlannerInfo *root,
  add_path(baserel, (Path *) path);

  /* Add paths with pathkeys */
- add_paths_with_pathkeys_for_rel(root, baserel, NULL);
+ add_paths_with_pathkeys_for_rel(root, baserel, NULL, NULL);

* I dropped this test case, because it would not be stable if the
system clock was too slow.