[C++] Zero-case union can't be imported via C Data Interface #14855
Description
The zero-case union is apparently not supported by Arrow C++'s C Data interface. I get:
'arrow_type' failed with Invalid: Invalid or unsupported format string: '+us:'
Reproducer for Python:
import pyarrow as pa
from pyarrow.cffi import ffi
empty_union = pa.sparse_union([])
ptr = ffi.new("struct ArrowSchema*")
empty_union._export_to_c(int(ffi.cast("uintptr_t", ptr)))
pa.DataType._import_from_c(int(ffi.cast("uintptr_t", ptr)))
# Traceback (most recent call last):
# File "<stdin>", line 1, in <module>
# File "pyarrow/types.pxi", line 248, in pyarrow.lib.DataType._import_from_c
# File "pyarrow/error.pxi", line 144, in pyarrow.lib.pyarrow_internal_check_status
# File "pyarrow/error.pxi", line 100, in pyarrow.lib.check_status
# pyarrow.lib.ArrowInvalid: Invalid or unsupported format string: '+us:'Originally posted by @paleolimbot in apache/arrow-nanoarrow#81 (comment)
Component(s)
C++