[Distutils] Draft PEP for JSON based metadata published

[Donald Stufft]

I feel like we are still conflating some names and use cases here with
source_label, source_url, source reference, and the is operator.

source_label // source_url - References to the source that is associated
with this release. Must not point to anything besides source (no whls,
no other built or platform specific artifact).

is // source reference - This is where my real issue comes into play.

I almost think that it doesn't make any sense to allow an is comparison
to a source label. In Python `is` is an identity function and a source
label is not a directly installable thing. It must be built first (even
if building involves simply copying .py files into a whl).

I don't like using the word "source" here because when pointing at an
url it could be a whl file, it could be an egg, it could be a source
archive.

I'm not sure what should be done about the non url form of ``is``. The
url form makes sense to me because an url is (theortically) an identity
pointer to an exact installable. However a source_label is not, it could
have any number of installable files associated with it and the one you
install may be dependent upon what OS you're using or what Python
version your using.

-- 
  Donald Stufft
  donald at stufft.io