[Distutils] Commit 17f89f4 "Update sdist to use sdist_add_defaults forward compatibility"

[Brandon Casey]

Hi Jason,

I just started looking at the setuptools repo last night to see if I
could figure out why setuptools doesn't place data_files inside an
sdist and I saw your commit 17f89f4 to teach the sdist command to use
the python 36 compatibility behavior.  But it overrides
_add_defaults_data_files() which actually adds the data_files to the
filelist, and replaces it with an empty function.

If I remove this function, so that the one from
py36compat.sdist_add_defaults is used, then it seems to work correctly
for me.  But that is the extent of my testing so far.

The doc comment for the new _add_defaults_data_files function just says:

   Don't add any data files, but why?

I see _add_defaults_python() was also overridden and is now only
slightly different from the one in py36compat.sdist_add_defaults.  It
looks like maybe you were just trying to make use of the py36compat
functions without introducing any change in behavior.  Is that the
only reason that _add_defaults_python() differs from the one in
py36compat and why _add_defaults_data_files is disabled?  Or do you
have some concerns about enabling this functionality?  Any thoughts of
enabling it?  If there's some active discussion or explanation on a
mailing list somewhere, please feel free to point me towards that.

Thanks,
-Brandon