"ValueError: Input array must be contiguous" when *cast_value* codec next to *transpose* codec

[raphaeljolivet]

Zarr version

v3.3.1.dev3+g976be695

Numcodecs version

v0.16.5

Python Version

3.12.11

Operating System

Debian

Installation

uv sync

Description

When combined with the transpose codec cast_value fails because the array is not continugous.

According to the specification,
the transpose codec is expected to produce "views".

Thus, it should be the responsibility of every codec to ensure it makes it contiguous, if needed.

If my interpretation is correct, I will prepare a PR to fix this, with proper unit test.
I guess we should test the behavior on every other codec ...

Steps to reproduce

def test_enforce_contiguous_arrays() :
    """
    Transpose codec produces non continguous arrays.
    Ensure cast_value make them contiguous before processing.
    """
    data = np.arange(20, dtype=np.float32).reshape(5, 2, 2)

    def make_array(filters):
        return zarr.create_array(
            store=MemoryStore(),
            shape=data.shape,
            dtype=data.dtype,
            chunks=data.shape,
            filters=filters,
            serializer=zarr.codecs.BytesCodec(endian="little"),
            compressors=None,
            zarr_format=3,
        )

    # Cast before tranpose : may fail on read.
    array = make_array([
        zarr.codecs.CastValue(data_type="uint16"),
        zarr.codecs.TransposeCodec(order=(1, 2, 0)),
    ])

    # Write should be ok
    array[:] = data

    # Read may fail
    assert_array_equal(array[:], data)

    # Cast after tranpose : may fail on write
    array = make_array([
        zarr.codecs.TransposeCodec(order=(1, 2, 0)),
        zarr.codecs.CastValue(data_type="uint16"),
    ])

    # Write may fail
    array[:] = data

# Read should be ok
assert_array_equal(array[:], data)

Additional output

No response

[d-v-b]

thanks for the report, this looks like a bug in cast_value. it should be changed to handle non-contiguous arrays.

[raphaeljolivet]

I just did a PR

The "lint" CI fails while prek works fine locally.
I am not sure why.