fix: drop zero-cost views of ak.Array

[agoose77]

In the words of Taylor Swift, I'm the problem — it's me.

In #2649, I exposed a DLPack view of Awkward Arrays, alongside the __array_interface__ and __cuda_array_interface__ properties. However, these are supposed to be zero copy, and non-owned views. As such, we can't return local temporary copies that leave scope.

So, whoops, and here's a fix: we don't support DLPack or CUDA views of Awkward Arrays; they need to be explicitly converted to user-referenced backend arrays.

[agoose77]

@lgray this will be in the next release, ASAP.

[codecov]

Codecov Report

Merging #2697 (98fce24) into main (684a84d) will increase coverage by 0.01%.
The diff coverage is 75.00%.

Additional details and impacted files

Files Changed	Coverage Δ
src/awkward/highlevel.py	76.84% <66.66%> (+0.45%)	⬆️
src/awkward/_connect/numpy.py	91.62% <80.00%> (-0.27%)	⬇️
src/awkward/_connect/dlpack.py	100.00% <100.00%> (+7.14%)	⬆️

[ikrommyd]

Fixes my code as seen in the output of the last cell here: https://github.com/iasonkrom/egamma-tnp/blob/debug_dask_histogram/debug_dask_histogram.ipynb

[jpivarski]

I had thought that __cuda_array_interface__ and __dlpack_device__ would only affect rectilinear arrays on GPUs, and these don't have applications yet.

That might still be true. It may be that the __array_interface__ is the one that's causing the trouble. Yes, hist uses it:

>>> class Something:
...     __array_interface__ = {"data": np.arange(10), "shape": (10,), "typestr": "<i8"}
... 
>>> hist.Hist.new.Reg(10, 0, 10).Double().fill(Something())
Hist(Regular(10, 0, 10, label='Axis 0'), storage=Double()) # Sum: 10.0

CuPy uses __cuda_array_interface__ but nobody else does:

>>> data = cp.arange(10)
>>> data.__cuda_array_interface__
{'shape': (10,), 'typestr': '<i8', 'descr': [('', '<i8')], 'stream': 1, 'version': 3, 'strides': None, 'data': (140416645071360, False)}
>>> class Something:
...     __cuda_array_interface__ = {"data": (140416645071360, False), "shape": (10,), "typestr": "<i8", "stream": 1, "version": 3}
... 
>>> cp.asarray(Something())
array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])

(The above worked, but both of the below didn't.)

```python
>>> np.asarray(Something())
array(<__main__.Something object at 0x7fb574e86cd0>, dtype=object)
>>> hist.Hist.new.Reg(10, 0, 10).Double().fill(Something())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/jpivarski/mambaforge/lib/python3.9/site-packages/hist/basehist.py", line 232, in fill
    return super().fill(*args, *data, weight=weight, sample=sample, threads=threads)
  File "/home/jpivarski/mambaforge/lib/python3.9/site-packages/boost_histogram/_internal/hist.py", line 529, in fill
    self._hist.fill(*args_ars, weight=weight_ars, sample=sample_ars)  # type: ignore[arg-type]
TypeError: float() argument must be a string or a number, not 'Something'

I haven't managed to get the DLPack protocol to be identified by anything:

>>> from awkward._connect.dlpack import DLPackDevice
>>> class Something:
...     def __dlpack_device__(self):
...         return DLPackDevice.CPU
...     def __dlpack__(self, stream=None):
...         return np.arange(10)

On Slack, @agoose77 said he'd split out the __cuda_array_interface__ and __dlpack_device__ removals into a different PR because they have a different motivation than the __array_interface__ removal. The __array_interface__ removal is for fixing #2695, and this is the right fix for that.

[ikrommyd]

Would it be possible to roll out a patch 2.4.2 release?