On 28 August 2017 at 20:32, Thomas Kluyver <thomas@kluyver.me.uk> wrote:
On Mon, Aug 28, 2017, at 08:20 PM, Paul Moore wrote:
Maybe we go fully to Nick's proposal that we don't mandate any sort of consistency constraints in the PEP. That would mean pip *has* to go sdist->wheel (because pip does need consistent behaviour), and xoviat's setuptools backend can skip building a sdist on the way to building a wheel. It also means that the build_wheel hook is essentially unreliable in isolation, and that all frontends will likely have to do the build_sdist->build_wheel with fallback to inplace build_wheel dance that pip does. But we expect many less frontends than backends, so maybe that's the right trade-off?
I've mentioned this before, but I have little faith in our ability to predict that one side of an interface will be far more numerous than the other. This is partly from my experience with Jupyter, where we got that prediction completely wrong. But I also think it's quite plausible that many frontend tools will want to use this interface (to argue against myself, most will be Python tools, so they could theoretically share a common wrapper module - but I have some doubts about whether they will).
I'm not saying we shouldn't do this - as Donald is firmly in favour and you're wavering, it seems the easier option to wrap the discussion up. But I'm suspicious of the rationale that *there will be fewer frontends so they should have more responsibility*.
Me too. At the moment, I only expect two backends of any substance - your flit backend and xoviat's setuptools one. But I only know of one frontend, namely pip - and talk of projects like tox or twine acting as frontends never seems to get any traction. The problem is that xoviat has to do a lot of work to provide guarantees that flit gets essentially for free, but flit can't provide the guaranteed sdist->wheel route that would let pip just go sdist->wheel cleanly. So there's a mismatch of requirements and *someone* needs to plaster over the cracks. At the moment, the debate is essentially whether that's xoviat or pip. Donald wants it to be pip because we can't guarantee that the next backend developer will be aware of all of the issues we debated here, and so we have to protect against that. I was persuaded[1] that we could document the requirements in the spec and expect that to be enough. I do worry that there's a risk that we're crippling the PEP with sufficient complexity that no-one will bother writing alternative frontends *or* additional backends (although I hope your support library might ease that problem somewhat). My main motivation for wavering is that I thought agreeing to trust the backend would simplify many of the decisions, and it's immensely frustrating to me that we're still debating the same question in the "return None" thread. Paul [1] I don't say "I thought" because I *never* thought backends would be sufficiently reliable. I just accepted that my concerns are only hypothetical. I wish others could do the same :-(