array_concat fails with internal error on mixed List + LargeList inputs

[hcrosse]

Describe the bug

Calling array_concat with a mix of List and LargeList arguments hits an internal cast error:

> select array_concat(make_array(1, 2), arrow_cast([3, 4], 'LargeList(Int64)'));
DataFusion error: Internal error: could not cast array of type List(Int64) to arrow_array::array::list_array::GenericListArray<i64>.

The issue is in ArrayConcat::coerce_types (datafusion/functions-nested/src/concat.rs). It uses the return type's base element type to coerce items but leaves the container variant alone, so a List input isn't coerced to LargeList when the return type is LargeList. Then array_concat_inner tries to downcast the List array to GenericListArray<i64> and fails.

Same symptom for FixedSizeList + LargeList.

To Reproduce

select array_concat(make_array(1, 2), arrow_cast([3, 4], 'LargeList(Int64)'));
select array_concat(arrow_cast([1, 2], 'FixedSizeList(2, Int64)'), arrow_cast([3, 4], 'LargeList(Int64)'));

Expected behavior

[1, 2, 3, 4] returned as LargeList(Int64) in both cases (the widest container variant).

Additional context

Surfaced while reviewing #21689, which rewrites concat(array, ...) to array_concat(array, ...) and inherits this limitation for concat(List, LargeList).

[hcrosse]

take