Make pull_var_clause() handle GroupingFuncs exactly like Aggrefs.

This follows in the footsteps of commit 2591ee8ec by removing one more
ill-advised shortcut from planning of GroupingFuncs.  It's true that
we don't intend to execute the argument expression(s) at runtime, but
we still have to process any Vars appearing within them, or we risk
failure at setrefs.c time (or more fundamentally, in EXPLAIN trying
to print such an expression).  Vars in upper plan nodes have to have
referents in the next plan level, whether we ever execute 'em or not.

Per bug #17479 from Michael J. Sullivan.  Back-patch to all supported
branches.

Richard Guo

Discussion: https://postgr.es/m/17479-6260deceaf0ad304@postgresql.org

src/backend/optimizer/util/var.c

@@ -579,7 +579,7 @@ locate_var_of_level_walker(Node *node,
  *	  Vars within a PHV's expression are included in the result only
  *	  when PVC_RECURSE_PLACEHOLDERS is specified.
  *
- *	  GroupingFuncs are treated mostly like Aggrefs, and so do not need
+ *	  GroupingFuncs are treated exactly like Aggrefs, and so do not need
  *	  their own flag bits.
  *
  *	  CurrentOfExpr nodes are ignored in all cases.
@@ -654,13 +654,7 @@ pull_var_clause_walker(Node *node, pull_var_clause_context *context)
 		}
 		else if (context->flags & PVC_RECURSE_AGGREGATES)
 		{
-			/*
-			 * We do NOT descend into the contained expression, even if the
-			 * caller asked for it, because we never actually evaluate it -
-			 * the result is driven entirely off the associated GROUP BY
-			 * clause, so we never need to extract the actual Vars here.
-			 */
-			return false;
+			/* fall through to recurse into the GroupingFunc's arguments */
 		}
 		else
 			elog(ERROR, "GROUPING found where not expected");

src/test/regress/expected/groupingsets.out

@@ -466,6 +466,70 @@ where x = 1 and q1 = 123;
 ---+----+-----
 (0 rows)
 
+-- check handling of pulled-up SubPlan in GROUPING() argument (bug #17479)
+explain (verbose, costs off)
+select grouping(ss.x)
+from int8_tbl i1
+cross join lateral (select (select i1.q1) as x) ss
+group by ss.x;
+                   QUERY PLAN                   
+------------------------------------------------
+ GroupAggregate
+   Output: GROUPING((SubPlan 1)), ((SubPlan 2))
+   Group Key: ((SubPlan 2))
+   ->  Sort
+         Output: ((SubPlan 2)), i1.q1
+         Sort Key: ((SubPlan 2))
+         ->  Seq Scan on public.int8_tbl i1
+               Output: (SubPlan 2), i1.q1
+               SubPlan 2
+                 ->  Result
+                       Output: i1.q1
+(11 rows)
+
+select grouping(ss.x)
+from int8_tbl i1
+cross join lateral (select (select i1.q1) as x) ss
+group by ss.x;
+ grouping 
+----------
+        0
+        0
+(2 rows)
+
+explain (verbose, costs off)
+select (select grouping(ss.x))
+from int8_tbl i1
+cross join lateral (select (select i1.q1) as x) ss
+group by ss.x;
+                 QUERY PLAN                 
+--------------------------------------------
+ GroupAggregate
+   Output: (SubPlan 2), ((SubPlan 3))
+   Group Key: ((SubPlan 3))
+   ->  Sort
+         Output: ((SubPlan 3)), i1.q1
+         Sort Key: ((SubPlan 3))
+         ->  Seq Scan on public.int8_tbl i1
+               Output: (SubPlan 3), i1.q1
+               SubPlan 3
+                 ->  Result
+                       Output: i1.q1
+   SubPlan 2
+     ->  Result
+           Output: GROUPING((SubPlan 1))
+(14 rows)
+
+select (select grouping(ss.x))
+from int8_tbl i1
+cross join lateral (select (select i1.q1) as x) ss
+group by ss.x;
+ grouping 
+----------
+        0
+        0
+(2 rows)
+
 -- simple rescan tests
 select a, b, sum(v.x)
   from (values (1),(2)) v(x), gstest_data(v.x)

src/test/regress/sql/groupingsets.sql

@@ -188,6 +188,29 @@ select * from (
 ) ss
 where x = 1 and q1 = 123;
 
+-- check handling of pulled-up SubPlan in GROUPING() argument (bug #17479)
+explain (verbose, costs off)
+select grouping(ss.x)
+from int8_tbl i1
+cross join lateral (select (select i1.q1) as x) ss
+group by ss.x;
+
+select grouping(ss.x)
+from int8_tbl i1
+cross join lateral (select (select i1.q1) as x) ss
+group by ss.x;
+
+explain (verbose, costs off)
+select (select grouping(ss.x))
+from int8_tbl i1
+cross join lateral (select (select i1.q1) as x) ss
+group by ss.x;
+
+select (select grouping(ss.x))
+from int8_tbl i1
+cross join lateral (select (select i1.q1) as x) ss
+group by ss.x;
+
 -- simple rescan tests
 
 select a, b, sum(v.x)