Better fix for permissions tests in excluded subqueries.

This reverts the code changes in 50c137487c96e629e0e5372bb3d1b5f1a2f71a88,
which turned out to induce crashes and not completely fix the problem
anyway.  That commit only considered single subqueries that were excluded
by constraint-exclusion logic, but actually the problem also exists for
subqueries that are appendrel members (ie part of a UNION ALL list).  In
such cases we can't add a dummy subpath to the appendrel's AppendPath list
without defeating the logic that recognizes when an appendrel is completely
excluded.  Instead, fix the problem by having setrefs.c scan the rangetable
an extra time looking for subqueries that didn't get into the plan tree.
(This approach depends on the 9.2 change that made set_subquery_pathlist
generate dummy paths for excluded single subqueries, so that the exclusion
behavior is the same for single subqueries and appendrel members.)

Note: it turns out that the appendrel form of the missed-permissions-checks
bug exists as far back as 8.4.  However, since the practical effect of that
bug seems pretty minimal, consensus is to not attempt to fix it in the back
branches, at least not yet.  Possibly we could back-port this patch once
it's gotten a reasonable amount of testing in HEAD.  For the moment I'm
just going to revert the previous patch in 9.2.

1 files changed, 7 insertions, 26 deletions

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index e43ef3aa898..52bab79007e 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -678,8 +678,7 @@ static Plan *
 create_append_plan(PlannerInfo *root, AppendPath *best_path)
 {
 	Append	   *plan;
-	RelOptInfo *rel = best_path->path.parent;
-	List	   *tlist = build_relation_tlist(rel);
+	List	   *tlist = build_relation_tlist(best_path->path.parent);
 	List	   *subplans = NIL;
 	ListCell   *subpaths;
 
@@ -694,30 +693,12 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path)
 	 */
 	if (best_path->subpaths == NIL)
 	{
-		/*
-		 * If this is a dummy path for a subquery, we have to wrap the
-		 * subquery's original plan in a SubqueryScan so that setrefs.c will
-		 * do the right things.  (In particular, it must pull up the
-		 * subquery's rangetable so that the executor will apply permissions
-		 * checks to those rels at runtime.)
-		 */
-		if (rel->rtekind == RTE_SUBQUERY)
-		{
-			Assert(is_dummy_plan(rel->subplan));
-			return (Plan *) make_subqueryscan(tlist,
-											  NIL,
-											  rel->relid,
-											  rel->subplan);
-		}
-		else
-		{
-			/* Generate a Result plan with constant-FALSE gating qual */
-			return (Plan *) make_result(root,
-										tlist,
-									 (Node *) list_make1(makeBoolConst(false,
-																	 false)),
-										NULL);
-		}
+		/* Generate a Result plan with constant-FALSE gating qual */
+		return (Plan *) make_result(root,
+									tlist,
+									(Node *) list_make1(makeBoolConst(false,
+																	  false)),
+									NULL);
 	}
 
 	/* Build the plan for each child */