Warn when anndata.concat join=outer fails because of a mismatch of layers

[pakiessling]

Please describe your wishes and possible alternatives to achieve the desired result.

I just had something similiar to this happen:

import scanpy as sc, anndata as ad
print(sc.__version__, ad.__version__)
>1.9.6 0.10.4
pbmc = sc.datasets.pbmc68k_reduced()
pbmc1 = pbmc[:,:300].copy()
pbmc2 = pbmc[:,300:].copy()
pbmc1.layers["test"] = pbmc1.X.copy()

joined = ad.concat([pbmc1, pbmc2], join="outer",axis=1)
>IndexError: indices are out-of-bounds

And it took me a while to figure out that the problem was the outer join in combination with the layer mismatch.
Would it be possible to warn the user, that that is the problem?

[ivirshup]

I can replicate. Thanks for the bug report!

Interesting that it doesn't happen when axis=0....