TST: np.fix check fails with numpy-dev (TypeError: cannot write to unmasked output)

[pllim]

Started popping up in numpy-dev jobs. @mhvk is investigating.

____________________________ TestUfuncLike.test_fix ____________________________

self = <astropy.utils.masked.tests.test_function_helpers.TestUfuncLike object at 0x7fdd354916c0>

    def test_fix(self):
>       self.check(np.fix)

astropy/utils/masked/tests/test_function_helpers.py:672: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
astropy/utils/masked/tests/test_function_helpers.py:75: in check
    o = func(self.ma, *args, **kwargs)
astropy/utils/masked/core.py:842: in __array_function__
    return super().__array_function__(function, types, args, kwargs)
numpy/lib/ufunclike.py:62: in fix
    res = nx.floor(x, out=res, where=nx.greater_equal(x, 0))
astropy/utils/masked/core.py:828: in __array_ufunc__
    result = getattr(ufunc, method)(*unmasked, **kwargs)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = MaskedNDArray([[  ———,  True,  True],
               [ True,   ———,  True]])
ufunc = <ufunc 'floor'>, method = '__call__'
inputs = (array([[0., 1., 2.],
       [3., 4., 5.]]),)
kwargs = {'where': MaskedNDArray([[  ———,  True,  True],
               [ True,   ———,  True]])}
out = (array([[0., 1., 2.],
       [3., 4., 5.]]),)
out_unmasked = (array([[0., 1., 2.],
       [3., 4., 5.]]),), out_mask = None
out_masks = (None,), d = array([[0., 1., 2.],
       [3., 4., 5.]]), m = None

    def __array_ufunc__(self, ufunc, method, *inputs, **kwargs):
        out = kwargs.pop("out", None)
        out_unmasked = None
        out_mask = None
        if out is not None:
            out_unmasked, out_masks = self._get_data_and_masks(*out)
            for d, m in zip(out_unmasked, out_masks):
                if m is None:
                    # TODO: allow writing to unmasked output if nothing is masked?
                    if d is not None:
>                       raise TypeError("cannot write to unmasked output")
E                       TypeError: cannot write to unmasked output

astropy/utils/masked/core.py:701: TypeError

[mhvk]

Ah, yes, that was numpy/numpy#23240 and we actually checked in that discussion whether it would pose problems for astropy - numpy/numpy#23240 (comment) - conclusion was that only np.fix was affected and that it would be a trivial fix. I'll make that now...

[pllim]

@mhvk , any update on this? 🙏

[byrdie]

@mhvk, if you haven't started on this yet I could attempt to fix this since I'm the one who messed it up.

[mhvk]

I got a simple fix that will work for all versions, and a more complicated one, which allows Masked to deal with masked where generally that would be good for the next version (since it is an API change). Let me just push up the simple one; I can always revert that for the more complete version.

[mhvk]

See #14589

[mhvk]

See updated and better fix for 5.3 in #14590, with a simpler fix for 5.2.2 and 5.0.6 in #14591.

[mhvk]

@byrdie - review of #14590 would be most appreciated!