On 8 October 2015 at 04:32, Erik Bray <erik.m.bray@gmail.com> wrote:
Starting a sub-thread since issues with pbr are orthogonal to the original disucssion.
But one point I'd like to raise about this is that when I originally designed d2to1, on which a chunk of pbr is based, it was *explicitly* designed to never be installed in site-packages (with the exception of downstream packaging systems which can do what they want and are more controlled). This is exactly because I knew different packages might have dependencies on different versions of d2to1 as features are added, and that if some version is installed in site-packages it can lead to VersionConflict issues (this is in part exacerbated by a bug/misfeature in setuptools--I fixed that bug a while ago but the fix had to be rolled back due to a regression [1]).
So yes - that principle makes a lot of sense. There are two factors for pbr. a) as Donald mentions, there's a runtime API too - but we could indeed split that out into a separate package, if it would help things. b) more importantly, in OpenStack infra we can't use easy-install - its inconsistency with pip and lack of updated handling for wheels, HTTPS, separate configuration - consistently cause headaches every single time it happens. So many years ago we put in place pre-installation of all known build-time dependencies - we just install them statically, because we find the effort required to make them be compatible is less than the headaches from easy-install. As such pbr has a hard API requirement: thou shalt be backwards compatible. Clearly b) can hit VersionConflicts if pbr (and any other build dependencies like setuptools itself) are out of date, but that is easily handled for automated environments (pip install -U pip setuptools wheel pbr && echo YAY), and it errors cleanly enough for hand-use by folk that its a decent enough tradeoff in our experience.
I don't know what features pbr has grown that might make someone want it to be a runtime dependency (the only entry-points I noticed were for adding egg-info writers but that should only be needed at build-time too...), but maybe something like that should be split off as a separate module or something...
Its all about easy-install. This is why I put a proof of concept static-setup-requires thing together for pip (and its on our teams roadmap to deliver a production version of it via patches to all the pypa projects, we're just not at that point yet - the resolver is first, and we have to finish rolling out constraints within OpenStack before that gets large timeslices). -Rob -- Robert Collins <rbtcollins@hp.com> Distinguished Technologist HP Converged Cloud