Fix assert failure in expand_grouping_sets

linitial_node() fails in assert enabled builds if the given pointer is
not of the specified type.  Here the type is IntList.  The code thought
it should be expecting List, but it was wrong.

In the existing tests which run this code the initial list element is
always NIL.  Since linitial_node() allows NULL, we didn't trigger any
assert failures in the existing regression tests.

There is still some discussion as to whether we need a few more tests in
this area, but for now, since beta2 is looming, fix the bug first.

Bug: #17067
Discussion: https://postgr.es/m/17067-665d50fa321f79e0@postgresql.org
Reported-by: Yaoguang Chen

diff --git a/src/backend/parser/parse_agg.c b/src/backend/parser/parse_agg.c
index 9562ffcf3e2bc4a155babf382d109c786fed891f..a25f8d5b98991d15059a0df46d6fdb43a6dc56be 100644 (file)
--- a/src/backend/parser/parse_agg.c
+++ b/src/backend/parser/parse_agg.c
@@ -1855,7 +1855,7 @@ expand_grouping_sets(List *groupingSets, bool groupDistinct, int limit)
        list_sort(result, cmp_list_len_contents_asc);
 
        /* Finally, remove duplicates */
-       prev = linitial_node(List, result);
+       prev = linitial(result);
        for_each_from(cell, result, 1)
        {
            if (equal(lfirst(cell), prev))