Fix setrefs.c code for Result Cache nodes

Result Cache, added in 9eacee2e neglected to properly adjust the plan
references in setrefs.c.  This could lead to the following error during
EXPLAIN:

ERROR:  cannot decompile join alias var in plan tree

Fix that.

Bug: 17030
Reported-by: Hans Buschmann
Discussion: https://postgr.es/m/17030-5844aecae42fe223@postgresql.org

src/backend/optimizer/plan/setrefs.c

@@ -756,6 +756,12 @@ set_plan_refs(PlannerInfo *root, Plan *plan, int rtoffset)
 			{
 				ResultCache *rcplan = (ResultCache *) plan;
 
+				/*
+				 * Result Cache does not evaluate its targetlist.  It just
+				 * uses the same targetlist from its outer subnode.
+				 */
+				set_dummy_tlist_references(plan, rtoffset);
+
 				rcplan->param_exprs = fix_scan_list(root, rcplan->param_exprs,
 													rtoffset,
 													NUM_EXEC_TLIST(plan));

src/test/regress/expected/join.out

@@ -4216,8 +4216,8 @@ where t1.f1 = ss.f1;
                     QUERY PLAN                    
 --------------------------------------------------
  Nested Loop
-   Output: t1.f1, i8.q1, i8.q2, q1, f1
-   Join Filter: (t1.f1 = f1)
+   Output: t1.f1, i8.q1, i8.q2, (i8.q1), t2.f1
+   Join Filter: (t1.f1 = t2.f1)
    ->  Nested Loop Left Join
          Output: t1.f1, i8.q1, i8.q2
          ->  Seq Scan on public.text_tbl t1
@@ -4228,7 +4228,7 @@ where t1.f1 = ss.f1;
                      Output: i8.q1, i8.q2
                      Filter: (i8.q2 = 123)
    ->  Result Cache
-         Output: q1, f1
+         Output: (i8.q1), t2.f1
          Cache Key: i8.q1
          ->  Limit
                Output: (i8.q1), t2.f1
@@ -4256,12 +4256,12 @@ select * from
   lateral (select ss1.* from text_tbl t3 limit 1) as ss2
 where t1.f1 = ss2.f1;
                             QUERY PLAN                             
---------------------------------------------------------
+-------------------------------------------------------------------
  Nested Loop
-   Output: t1.f1, i8.q1, i8.q2, q1, f1, q1, f1
-   Join Filter: (t1.f1 = f1)
+   Output: t1.f1, i8.q1, i8.q2, (i8.q1), t2.f1, ((i8.q1)), (t2.f1)
+   Join Filter: (t1.f1 = (t2.f1))
    ->  Nested Loop
-         Output: t1.f1, i8.q1, i8.q2, q1, f1
+         Output: t1.f1, i8.q1, i8.q2, (i8.q1), t2.f1
          ->  Nested Loop Left Join
                Output: t1.f1, i8.q1, i8.q2
                ->  Seq Scan on public.text_tbl t1
@@ -4272,19 +4272,19 @@ where t1.f1 = ss2.f1;
                            Output: i8.q1, i8.q2
                            Filter: (i8.q2 = 123)
          ->  Result Cache
-               Output: q1, f1
+               Output: (i8.q1), t2.f1
                Cache Key: i8.q1
                ->  Limit
                      Output: (i8.q1), t2.f1
                      ->  Seq Scan on public.text_tbl t2
                            Output: i8.q1, t2.f1
    ->  Result Cache
-         Output: q1, f1
-         Cache Key: q1, f1
+         Output: ((i8.q1)), (t2.f1)
+         Cache Key: (i8.q1), t2.f1
          ->  Limit
-               Output: (q1), (f1)
+               Output: ((i8.q1)), (t2.f1)
                ->  Seq Scan on public.text_tbl t3
-                     Output: q1, f1
+                     Output: (i8.q1), t2.f1
 (28 rows)
 
 select * from