Calculate agglevelsup correctly when Aggref contains a CTE.

If an aggregate function call contains a sub-select that has
an RTE referencing a CTE outside the aggregate, we must treat
that reference like a Var referencing the CTE's query level
for purposes of determining the aggregate's level.  Otherwise
we might reach the nonsensical conclusion that the aggregate
should be evaluated at some query level higher than the CTE,
ending in a planner error or a broken plan tree that causes
executor failures.

Bug: #19055
Reported-by: BugForge <dllggyx@outlook.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/19055-6970cfa8556a394d@postgresql.org
Backpatch-through: 13

src/test/regress/expected/with.out

@@ -2297,6 +2297,40 @@ from int4_tbl;
  -2147483647
 (5 rows)
 
+--
+-- test for bug #19055: interaction of WITH with aggregates
+--
+-- The reference to cte1 must determine the aggregate's level,
+-- even though it contains no Vars referencing cte1
+explain (verbose, costs off)
+select f1, (with cte1(x,y) as (select 1,2)
+            select count((select i4.f1 from cte1))) as ss
+from int4_tbl i4;
+                 QUERY PLAN                 
+--------------------------------------------
+ Seq Scan on public.int4_tbl i4
+   Output: i4.f1, (SubPlan 2)
+   SubPlan 2
+     ->  Aggregate
+           Output: count((InitPlan 1).col1)
+           InitPlan 1
+             ->  Result
+                   Output: i4.f1
+           ->  Result
+(9 rows)
+
+select f1, (with cte1(x,y) as (select 1,2)
+            select count((select i4.f1 from cte1))) as ss
+from int4_tbl i4;
+     f1      | ss 
+-------------+----
+           0 |  1
+      123456 |  1
+     -123456 |  1
+  2147483647 |  1
+ -2147483647 |  1
+(5 rows)
+
 --
 -- test for nested-recursive-WITH bug
 --

src/test/regress/sql/with.sql

@@ -1097,6 +1097,20 @@ select ( with cte(foo) as ( values(f1) )
           values((select foo from cte)) )
 from int4_tbl;
 
+--
+-- test for bug #19055: interaction of WITH with aggregates
+--
+-- The reference to cte1 must determine the aggregate's level,
+-- even though it contains no Vars referencing cte1
+explain (verbose, costs off)
+select f1, (with cte1(x,y) as (select 1,2)
+            select count((select i4.f1 from cte1))) as ss
+from int4_tbl i4;
+
+select f1, (with cte1(x,y) as (select 1,2)
+            select count((select i4.f1 from cte1))) as ss
+from int4_tbl i4;
+
 --
 -- test for nested-recursive-WITH bug
 --