I think the proposal is that flit depends on click depends on flit and neither one has a wheel and must be built from sdists. Then you have a circular build problem. So don't do that. I put this in the same category as accidentally conflicting with a stdlib module; it is confusing when it happens but it's also fairly avoidable.
On Sat, Jul 29, 2017, 17:38 Alex Grönholm <alex.gronh...@nextday.fi> wrote: > Donald Stufft kirjoitti 29.07.2017 klo 23:47: > > > On Jul 29, 2017, at 12:46 PM, Nathaniel Smith <n...@pobox.com> wrote: > > I guess the most obvious example of when this would occur is: suppose > click switches to using flit for builds, and then flit switches to using > click for command line parsing. Now there's a bit of a chicken and egg > problem where 'pip install click' will end up importing flit with the click > source tree on the path, and this tree of course contains a directory named > 'click', so unless special measures are taken flit will end up importing > the code it's trying to build. > > But of course this can happen for lots of reasons; most packages have > names that you wouldn't expect to randomly encounter at the root of a > source tree very often, but with 100,000+ packages on pypi I expect it will > happen eventually. > > This doesn't happen with setuptools because setuptools traditionally has > few or no dependencies, but obviously we're changing that; the whole idea > here is that now your build system has full access to pypi. > > > > This is something to be discouraged anyways, because it creates a sort of > broken situation (the same situation that setuptools itself had). The > problem is that if you’re starting from only sdists, you have a circular > dependency that cannot be broken. You can’t build click, because click > requires flit, but you can’t install flit, because flit requires click. The > only way to fix this is to either have an already built wheel that you can > use (which obviously was either built with a flit that didn’t require > click, or a click that didn’t require flit, or it’s provenance can be > traced back to that) or do some hacks that will hopefully resolve the > situation good enough to get your first wheel built. > > Setuptools tried to depend on things, and it broke shit for a lot of > people because of this. You basically can’t depend on anything as a build > system that uses you as a build system. You can only depend on things that > use other, different build systems in the entire dependency tree. Likely > the best thing for build systems to do is either have no dependencies, or > to have minimal dependencies that promise to only use setuptools (or > another build tool, which one doesn’t matter, just as long as it has no > dependencies) forever (and have setuptools or this other build tool promise > to never take a dependency). > > Or vendorize their dependencies? To me it seems unrealistic for a build > system to have no dependencies at all. Or perhaps this is exactly what you > meant :) > > > — > Donald Stufft > > > > > > _______________________________________________ > Distutils-SIG maillist - > Distutils-SIG@python.orghttps://mail.python.org/mailman/listinfo/distutils-sig > > > _______________________________________________ > Distutils-SIG maillist - Distutils-SIG@python.org > https://mail.python.org/mailman/listinfo/distutils-sig >
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