[Distutils] Installed Extras Metadata

[Nick Coghlan]

On 27 January 2018 at 13:46, Nathaniel Smith <njs at pobox.com> wrote:

> The advantages are:
>
> - it's a simpler way to record information the information you want
> here, without adding more special cases to dist-info: most code
> doesn't even have to know what 'extras' are, just what packages are
>
> - it opens the door to lots of more advanced features, like
> 'foo[test]' being a package that actually contains foo's tests, or
> build variants like 'numpy[mkl]' being numpy built against the MKL
> library, or maybe making it possible to track which version of numpy's
> ABI different packages use. (The latter two cases need some kind of
> provides: support, which is impossible right now because we don't want
> to allow random-other-package to say 'provides-dist: cryptography';
> but, it would be okay if 'numpy[mkl]' said 'provides-dist: numpy',
> because we know 'numpy[mkl]' and 'numpy' are maintained by the same
> people.)
>
> I know there's a lot of precedent for this kind of clever use of
> metadata-only packages in Debian (e.g. search for "metapackages"), and
> I guess the RPM world probably has similar tricks.
>

While I agree with this idea in principle, I'll note that RPM makes it
relatively straightforward to have a single SRPM emit multiple RPMs, so
defining a metapackage is just a few extra lines in a spec file. (I'm not
sure how Debian's metapackages work, but I believe they're similarly simple
on the publisher's side).

We don't currently have a comparable mechanism to readily allow a single
source project to expand to multiple package index entries that all share a
common sdist, but include different subsets in their respective wheel files
(defining one would definitely be possible, it's just a tricky migration
problem to work out).

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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