ORCA: align CBitSet vec_size for grouping-set bitsets

CreateGroupingSetsForRollup / Cube and the GROUPING_SET_EMPTY case in
GetColumnAttnosForGroupBy were constructing their accumulator/seed
CBitSets via the default ctor (vec_size = 256), then Union'ing in
per-grouping-set bitsets built with vec_size = num_cols.  CBitSet::Union
just splices in any missing CBitSetLinks wholesale, so the accumulator
ended up with a link at offset 0 (vec_size 256) plus a stray link at
offset num_cols (vec_size num_cols) covering the high tleSortGroupRef.
CBitSet::Get then computed the offset using the destination's
m_vector_size = 256 and never consulted the stray link, while
CBitSetIter happily walked both -- so Get(k) disagreed with the iterator
for any k >= num_cols.

In CreateDXLProjectNullsForGroupingSets this caused tleSortGroupRefs >=
num_cols to be misclassified as non-grouping columns and NULL'd out,
even in grouping sets that included them.  Visible as:

  select generate_series(1, a) g, a+b ab
    from (values (1,1),(2,2)) t(a,b)
    group by rollup(a, ab) order by 1,2;

returning 0 rows instead of 6 -- the rollup(a, ab) branch projected the
a column as NULL, so generate_series(1, NULL) produced no rows.

Fix by passing num_cols when constructing the accumulator and seed
bitsets so all participants in the Union share m_vector_size.

Add the repro to groupingsets.sql.

Author: yjhjstz

src/backend/gpopt/translate/CTranslatorUtils.cpp

@@ -918,7 +918,7 @@ CTranslatorUtils::GetColumnAttnosForGroupBy(
 			case GROUPING_SET_EMPTY:
 			{
 				col_attnos_arr_current = GPOS_NEW(mp) CBitSetArray(mp);
-				CBitSet *bset = GPOS_NEW(mp) CBitSet(mp);
+				CBitSet *bset = GPOS_NEW(mp) CBitSet(mp, num_cols);
 				col_attnos_arr_current->Append(bset);
 				break;
 			}
@@ -1113,11 +1113,15 @@ CTranslatorUtils::CreateGroupingSetsForRollup(CMemoryPool *mp,
 	GPOS_ASSERT(grouping_set->kind == GROUPING_SET_ROLLUP);
 	CBitSetArray *col_attnos_arr = GPOS_NEW(mp) CBitSetArray(mp);
 	ListCell *lc = nullptr;
-	CBitSet *current_result = GPOS_NEW(mp) CBitSet(mp);
+	// All grouping-set bitsets must share m_vector_size with the per-grouping-set
+	// bitsets built by CreateAttnoSetForGroupingSet (num_cols).  Mixing the default
+	// 256 with num_cols leaves misaligned CBitSetLink offsets after Union, causing
+	// Get() to disagree with the iterator.
+	CBitSet *current_result = GPOS_NEW(mp) CBitSet(mp, num_cols);
 	// Maintaining the order of grouping sets is essential because the
 	// UnionAll operator matches each child's distribution with the
 	// distribution of the first child
-	col_attnos_arr->Append(GPOS_NEW(mp) CBitSet(mp));
+	col_attnos_arr->Append(GPOS_NEW(mp) CBitSet(mp, num_cols));
 	ForEach(lc, grouping_set->content)
 	{
 		GroupingSet *gs_current = (GroupingSet *) lfirst(lc);
@@ -1152,8 +1156,9 @@ CTranslatorUtils::CreateGroupingSetsForCube(CMemoryPool *mp,
 	GPOS_ASSERT(grouping_set->kind == GROUPING_SET_CUBE);
 	CBitSetArray *col_attnos_arr = GPOS_NEW(mp) CBitSetArray(mp);
 
-	// add an empty set
-	col_attnos_arr->Append(GPOS_NEW(mp) CBitSet(mp));
+	// add an empty set — vec_size must match what CreateAttnoSetForGroupingSet
+	// produces (num_cols), otherwise Union below leaves misaligned links.
+	col_attnos_arr->Append(GPOS_NEW(mp) CBitSet(mp, num_cols));
 
 	ListCell *lc = nullptr;
 	ForEach(lc, grouping_set->content)

src/test/regress/expected/groupingsets.out

@@ -2470,4 +2470,18 @@ group by rollup (a,b) order by a;
    |   |    6
 (8 rows)
 
+-- ORCA: rollup over a derived-expression group alias with a target-list SRF.
+select generate_series(1, a) g, a+b ab
+  from (values (1,1),(2,2)) t(a,b)
+  group by rollup(a, ab) order by 1,2;
+ g | ab 
+---+----
+ 1 |  2
+ 1 |  4
+ 1 |   
+ 1 |   
+ 2 |  4
+ 2 |   
+(6 rows)
+
 -- end

src/test/regress/expected/groupingsets_optimizer.out

@@ -2645,4 +2645,18 @@ group by rollup (a,b) order by a;
    |   |    6
 (8 rows)
 
+-- ORCA: rollup over a derived-expression group alias with a target-list SRF.
+select generate_series(1, a) g, a+b ab
+  from (values (1,1),(2,2)) t(a,b)
+  group by rollup(a, ab) order by 1,2;
+ g | ab 
+---+----
+ 1 |  2
+ 1 |  4
+ 1 |   
+ 1 |   
+ 2 |  4
+ 2 |   
+(6 rows)
+
 -- end

src/test/regress/sql/groupingsets.sql

@@ -723,4 +723,9 @@ select a, b, rank(b) within group (order by b nulls last)
 from (values (1,1),(1,4),(1,5),(3,1),(3,2)) v(a,b)
 group by rollup (a,b) order by a;
 
+-- ORCA: rollup over a derived-expression group alias with a target-list SRF.
+select generate_series(1, a) g, a+b ab
+  from (values (1,1),(2,2)) t(a,b)
+  group by rollup(a, ab) order by 1,2;
+
 -- end