postgres_fdw: Avoid sharing list substructure.

list_concat(list_concat(a, b), c) destructively changes both a and b;
to avoid such perils, copy lists of remote_conds before incorporating
them into larger lists via list_concat().

Ashutosh Bapat, per a report from Etsuro Fujita

diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 465f43cd7c9a45d5c47d70e50c8418b4f3e2f322..d79e4ccbe3d6a9d2bf48d5e8e249f0738a1537cc 100644 (file)
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -3488,30 +3488,30 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
        {
                case JOIN_INNER:
                        fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
-                                                                                          fpinfo_i->remote_conds);
+                                                                                 list_copy(fpinfo_i->remote_conds));
                        fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
-                                                                                          fpinfo_o->remote_conds);
+                                                                                 list_copy(fpinfo_o->remote_conds));
                        break;
 
                case JOIN_LEFT:
                        fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
-                                                                                         fpinfo_i->remote_conds);
+                                                                                 list_copy(fpinfo_i->remote_conds));
                        fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
-                                                                                          fpinfo_o->remote_conds);
+                                                                                 list_copy(fpinfo_o->remote_conds));
                        break;
 
                case JOIN_RIGHT:
                        fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
-                                                                                         fpinfo_o->remote_conds);
+                                                                                 list_copy(fpinfo_o->remote_conds));
                        fpinfo->remote_conds = list_concat(fpinfo->remote_conds,
-                                                                                          fpinfo_i->remote_conds);
+                                                                                 list_copy(fpinfo_i->remote_conds));
                        break;
 
                case JOIN_FULL:
                        fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
-                                                                                         fpinfo_i->remote_conds);
+                                                                                 list_copy(fpinfo_i->remote_conds));
                        fpinfo->joinclauses = list_concat(fpinfo->joinclauses,
-                                                                                         fpinfo_o->remote_conds);
+                                                                                 list_copy(fpinfo_o->remote_conds));
                        break;
 
                default: