astropy: RTD failure due to plots involving convolution Kernels

This has now been fixed by matplotlib/matplotlib#22975 so the next release of matplotlib should contain the needed fix.

@WilliamJamieson - the difference from your minimal example and the real problem is, I think, that Kernel has a .shape defined and matplotlib sees this and treats the object as “sufficiently array-like”; without the shape, the object gets coerced to ndarray, and that works because of the __array__ method.

@mhvk you are exactly correct. See https://github.com/matplotlib/matplotlib/issues/22973#issuecomment-1117845296 where I just posted a better minimal reproducer. My above comment was me doing a first quick attempt.

@WilliamJamieson - the difference from your minimal example and the real problem is, I think, that Kernel has a .shape defined and matplotlib sees this and treats the object as “sufficiently array-like”; without the shape, the object gets coerced to ndarray, and that works because of the __array__ method.

I think this is due to https://github.com/matplotlib/matplotlib/pull/22141 (before that _check_1d was converting the input to a Numpy array with np.atleast_1d(x)). Probably worth a bug report.

Can you point me to which doc is failing? I’d think we could just imshow(kernel.array) in the docs and call it done, unless it’s really important that the __array__ magic works.

https://github.com/astropy/astropy/blob/5ddd6a39a1228da7599e75a71f402b08588dbd67/astropy/convolution/kernels.py#L75-L78

and the similar portions of each of the other kernels.

The __array__ magic is only a concern if it points at some sort of broken API on our end.