On Fri, 22 Jun 2018 at 10:19 Pradyun Gedam <pradyu...@gmail.com> wrote:
> > > On Fri, 22 Jun 2018, 22:31 Brett Cannon, <br...@python.org> wrote: > >> >> >> On Fri, 22 Jun 2018 at 09:35 Pradyun Gedam <pradyu...@gmail.com> wrote: >> >>> Hey everyone! >>> >>> In PEP 518, it is not clearly specified how a project that has a >>> pyproject.toml >>> file but has no build-system.requires should be treated (i.e. >>> build-system >>> table). >>> >>> In pip 10, such a pyproject.toml file was allowed and built with >>> setuptools >>> and wheel, which has resulted in a lot of projects making releases that >>> assumed >>> that such a pyproject.toml file is valid and they use setuptools and >>> wheel. >>> I understand that at least pytest, towncrier and Twisted might have done >>> so. >>> This happened since these projects have included configuration for >>> some tool in >>> pyproject.toml (some of which use only pyproject.toml for configuration >>> -- >>> black, towncrier). >>> >>> There's a little bit of subtlety here, in pip 10's implementation: >>> adding a >>> pyproject.toml file enables a new code path that does the build in >>> isolation >>> (in preparation for PEP 517; it's a good idea on it's own too) with only >>> the >>> build-system.requires packages available. When the >>> build-system.requires key >>> is missing, pip falls back to assuming it should be ["setuptools", >>> "wheel"]. >>> The in-development version of pip currently prints warnings when the key >>> is >>> not specified -- along the lines of "build-system.requires is missing" >>> + >>> "A future version of pip will reject pyproject.toml files that do not >>> comply >>> with PEP 518." and falls back to legacy behavior. >>> >>> Basically, pip 10 has a distinction between a missing pyproject.toml and >>> build-system.requires = ["setuptools", "wheel"] and the PEP doesn't. >>> However, >>> the PEP's precise wording here would help inform the debate about how pip >>> should behave in this edge case. >>> >> >> I think the precise wording is there by not having any wording. ;) If >> 'requires' was meant to be optional then the PEP would have said that. >> > > The PEP does say that the requires key is mandatory. Someone pointed out > on the pip's tracker that it doesn't say that the build-system table is > mandatory (or otherwise). > It says "There will be a [build-system] table in the configuration file to store build-related data". The word "will" does not suggest optional to me. ;) Once again, no one said "optional", so assume it's required. > And it seems that the JSON schema in the spec allows the table to be > skipped entirely. That's part of the reason for this thread. > The JSON schema is for "illustrative purposes only", so it should not be viewed as part of the spec. IOW if you need some authoritative judgement on this you have it from one of the co-authors of the PEP. :) -Brett > > >> >>> >>> I can think of at least 2 options for behavior when >>> build-system.requires is >>> missing: >>> >>> 1. Consider a missing build-system.requires equivalent to either a >>> missing >>> pyproject.toml or build-system.requires = ["setuptools", "wheel"]. >>> >>> 2. Making the build-system table mandatory in pyproject.toml. >>> >>> I personally think (2) would be fine -- "Explicit is better than >>> implicit." >>> >> >> And I think that's what pip's warning is saying the future will be, but >> they aren't quite yet ready to be that strict yet with their users (which I >> can understand). >> >> >>> >>> It'll be easy to detect and error out in this case, in a way that it's >>> possible >>> to provide meaningful information to the user about what to do here. >>> However, >>> this does mean that some existing releases of projects become >>> not-installable, >>> which is concerning; I do think the benefits outweigh the costs though. >>> >>> Thoughts on this? >>> >> >> I think what pip has planned with the warning makes sense. >> >
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