Reducers (sum/any/all) convert axis to regular axis with keepdims=True

[jrueb]

Version of Awkward Array

2.3.1

Description and code to reproduce

import awkward as ak

x = ak.Array([[1]])
result = ak.any(x, axis=1, keepdims=True)

The second axis of the results should be variable-length, because the second axis of x is also variable-length. However, the result is fully regular. I observe the same with ak.sum (among others). This did not happen in awkward version 1.10.3.

[agoose77]

Yes, this is intentional; we know that the axis has length-one, so we add that information.Is this a problem for you?

#1943 (comment) provides some context on the history of this decision :)

[jrueb]

I noticed this issue because I was slicing using the now-regular array, which removes a dimension.
In this case, I will use ak.from_regular to make sure its variable-length again. Thanks.