On 17 June 2017 at 17:07, Nathaniel Smith <njs@pobox.com> wrote:
On Fri, Jun 16, 2017 at 11:28 PM, Donald Stufft <donald@stufft.io> wrote:
On Jun 16, 2017, at 11:08 PM, Nathaniel Smith <njs@pobox.com> wrote:
(because the legacy setup.py command errors out, because the build_sdist hook is missing, because the build_sdist hook errors out...); probably falling back on shutil.copytree.
Ah okay. This is where the disconnect was. I assumed if a project was using a PEP 517 build tool the result of a build_sdist failure (or a build_wheel failure) would be surfacing an error to the end user, not some sort of fallback.
What we might be able to get away with in the PEP 517 transition is to provide an explicit way of signalling "build_sdist failed because that's just not a supported operation", so that pip could distinguish that from "something unexpected blew up" and only fall back in the first case.
That's what `prepare_wheel_input_files` gives us: if the backend doesn't implement it, then `build_sdist` is expected to always succeed, and any errors should be reported to the end user. OTOH, if `build_sdist` can fail (e.g. due to missing dependencies that aren't needed just to build a wheel), then the backend should offer a `prepare_wheel_input_files` that offers the expected guarantee (i.e. it will only fail for reasons that should be reported to the user attempting to do the build). The frontend then *won't* have a fallback copy strategy for PEP 517 backends - if `prepare_wheel_input_files` is present and fails, or if it's missing and `build_sdist` fails, then you have a failed wheel build on your hands. The legacy copying strategy would then only be used when falling all the way back to the `setup.py` interface, not as an attempt to continue the build in the face of a backend bug. This all gets murkier if you try to make the build_sdist hook more complex instead of just having two different hooks for frontends to call that tell the backend what the frontend actually wants (i.e. either an actual sdist, or just a clean set of exported files to use as input to a wheel build). Cheers, Nick. -- Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia