[Distutils] Towards a simple and standard sdist format that isn't intertwined with distutils

[David Cournapeau]

On Fri, Oct 2, 2015 at 12:58 PM, Donald Stufft <donald at stufft.io> wrote:

> On October 2, 2015 at 12:54:03 AM, Nathaniel Smith (njs at pobox.com) wrote:
> > > We realized that actually as far as we could tell, it wouldn't
> > be that
> > hard at this point to clean up how sdists work so that it would be
> > possible to migrate away from distutils. So we wrote up a little
> > draft
> > proposal.
> >
> > The main question is, does this approach seem sound?
>
> I've just read over your proposal, but I've also just woken up so I might
> be
> a little slow still! After reading what you have, I don't think that this
> proposal is the right way to go about improving sdists.
>
> The first thing that immediately stood out to me, is that it's recommending
> that downstream redistributors like Debian, Fedora, etc utilize Wheels
> instead
> of the sdist to build their packages from. However, that is not really
> going to
> fly with most (all?) of the downstream redistributors. Debian for instance
> has
> policy that requires the use of building all of it's packages from Source,
> not
> from anything else and Wheels are not a source package. While it can
> theoretically work for pure python packages, it quickly devolves into a
> mess
> when you factor in packages that have any C code what so ever.
>
> Overall, this feels more like a sidegrade than an upgrade. One major theme
> throughout of the PEP is that we're going to push to rely heavily on
> wheels as
> the primary format of installation. While that works well for things like
> Debian, I don't think it's going to work as wheel for us. If we were only
> distributing pure python packages, then yes absolutely, however given that
> we
> are not, we have to worry about ABI issues. Given that there is so many
> different environments that a particular package might be installed into,
> all
> with different ABIs we have to assume that installing from source is still
> going to be a primary path for end users to install and that we are never
> going
> to have a world where we can assume a Wheel in a repository.
>
> One of the problems with the current system, is that we have no mechanism
> by
> which to determine dependencies of a source distribution without
> downloading
> the file and executing some potentially untrusted code. This makes
> dependency
> resolution harder and much much slower than if we could read that
> information
> statically from a source distribution. This PEP doesn't offer anything in
> the
> way of solving this problem.
>
> To a similar tune, this PEP also doesn't make it possible to really get at
> any other metadata without executing software. This makes it pratically
> impossible to safely inspect an unknown or untrusted package to determine
> what
> it is and to get information about it. Right now PyPI relies on the
> uploading
> tool to send that information alongside of the file it is uploading, but
> honestly what it should be doing is extracting that information from
> within the
> file. This is sort of possible right now since distutils and setuptools
> both
> create a static metadata file within the source distribution, but we don't
> rely
> on that within PyPI because that information may or may not be accurate
> and may
> or may not exist. However the twine uploading tool *does* rely on that, and
> this PEP would break the ability for twine to upload a package without
> executing arbitrary code.
>
> Overall, I don't think that this really solves most of the foundational
> problems with the current format. Largely it feels that what it achieves is
> shuffling around some logic (you need to create a hook that you reference
> from
> within a .cfg file instead of creating a setuptools extension or so) but
> without fixing most of the problems. The largest benefit I see to
> switching to
> this right now is that it would enable us to have build time dependencies
> that
> were controlled by pip rather than installed implicitly via the execution
> of
> the setup.py. That doesn't feel like a big enough benefit to me to do a
> mass
> shakeup of what we recommend and tell people to do. Having people adjust
> and
> change and do something new requires effort, and we need something to
> justify
> that effort to other people and I don't think that this PEP has something
> we
> can really use to justify that effort.
>
> I *do* think that there is a core of some ideas here that are valuable,
> and in
> fact are similar to some ideas I've had. The main flaw I see here is that
> it
> doesn't really fix sdists, it takes a solution that would work for VCS
> checkouts and then reuses it for sdists. In my mind, the supported flow for
> package installation would be:
>
>     VCS/Bare Directory -> Source Distribution -> Wheel
>
> This would (eventually) be the only path that was supported for
> installation
> but you could "enter" the path at any stage. For example, if there is a
> Wheel
> already available, then you jump right on at the end and just install
> that, if
> there is a sdist available then pip first builds it into a wheel and then
> installs that, etc.
>
> I think your PEP is something like what the VCS/Bare Directory to sdist
> tooling
> could look like, but I don't think it's what the sdist to wheel path should
> look like.
>

A major feature of the proposal is to allow alternative build/packaging
tools.

If that proposal is not acceptable in its current form, how would you
envision interoperability between pip and new systems. For example, is it
realistic to encode which commands and options a setup.py would need to
support to be pip-installable (without the setup.py using distutils) ?

David
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