pip build command

Phase 2 from #5407

Allow pip to build packages for distribution - pip build

Some notes in https://github.com/pypa/pip/issues/5407#issuecomment-389621303

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pip now has PEP 517 support and uses build isolation by default on packages with pyproject.toml files – which means the way pip builds is difficult to reproduce externally in a trivial manner.

The pip build command would use the same code paths as PEP 517 with the sole difference being that it does not install the packages. It’s essentially the pip wheel in a PEP 517 world.

[pradyunsg]

I think we should still do this, using pypa/build or our existing code. We already host the logic for this, and I still feel that exposing this to users more directly would be a genuine usability improvement for them.

All frontends that are attempting to encapsulate the user workflow are providing a build command on their CLI as well, for usability reasons.

[pganssle]

I would like to suggest that this is probably a bad idea at least if the motivation is to create a recommended build tool to replace setup.py sdist bdist_wheel. I think instead we should have a simple dedicated tool for this purpose rather than a pip subcommand.

One reason for this is that build doesn’t obviously fit in either pip or twine - the only reason it makes sense for pip to have a build command is that pip already needs the ability to build packages in order to install them from source, but pip is generally a tool for consumers of packages, not for producers of packages. twine is usually for producers of packages but it has historically only acted upon already existing distributions and so while conceptually it makes sense for twine to be able to do the builds, it would in some sense change the nature of the tool from a tool that uploads things to PyPI into one that builds packages and uploads them to PyPI. To me, the fact that build has a reasonable claim to live in either package makes me think that build is its own thing and should be given its own package.

I’ll note that while it seems like pip “already needs the capability to do builds”, it in fact currently doesn’t need the ability to build source distributions, since it is perfectly capable of building wheels directly from the source. tox both needs and has the ability to build source distributions, but I would not really suggest adding a tox build command to expose this functionality.

Another reason to avoid adding this to pip is that pip already has some unifying themes to its subcommands, including huge reams of command line arguments, some shared and some not. For example, the pip wheel command already exists and is quite valuable for marshalling all the build artifacts one needs to install a given package because it gets you a wheel for the thing you want to install and all its dependencies; this is, however, a terrible and counter-intuitive behavior for a tool for building a wheel for upload - you need to do the magical pip wheel --no-deps -w dist/ . invocation to do what most people actually want to do. If we add a pip build command, we’ll suddenly either have to deprecate the existing and useful pip wheel command or we’ll confuse everyone by having two slightly different commands with very different purposes and semantics.

The one time where I think it would make sense for pip to have a pip build command would be if pip wants to move to a situation where instead of source builds going source → wheel → install, they would go source → sdist → wheel → install (for a consistent flow that produces artifacts at each stage), that would make sense, but even then I wouldn’t want to recommend it as “the way to create distributable artifacts”, but rather as a tool for marshalling resources.