The ultimate guide to EAPI 8

Three years ago, I had the pleasure of announcing EAPI 7 as a major step forward in our ebuild language. It introduced preliminary support for cross-compilation, it finally provided good replacements for the last Portagisms in ebuilds and it included many small changes that made ebuilds simpler.

Only a year and a half later, I have started working on the initial EAPI 8 feature set. Similarly to EAPI 6, EAPI 8 was supposed to focus on small changes and improvements. The two killer features listed below were already proposed at the time. I have prepared a few patches to the specification, as well as the initial implementation of the respective features for Portage. Unfortunately, the work stalled at the time.

Finally, as a result of surplus of free time last month, I was able to resume the work. Along with Ulrich Müller, we have quickly prepared the EAPI 8 feature set, got it pre-approved, prepared the specification and implemented all the features in Portage and pkgcore. Last Sunday, the Council has approved EAPI 8 and it’s now ready for ~arch use.

What’s there in EAPI 8? Well, for a start we have install-time dependencies (IDEPEND) that fill a gap in our cross-compilation design. Then, selective fetch/mirror restriction make it easier to combine proprietary and free distfiles in a single package. PROPERTIES and RESTRICT are now accumulated across eclasses reducing confusion for eclass writers. There’s dosym -r to create relative symlinks conveniently from dynamic paths. Plus bunch of other improvements, updates and cleanups.

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DISTUTILS_USE_SETUPTOOLS, QA spam and… more QA spam?

Update: the information provided in this post is out of date. As of today, Python 3.7 is no longer relevant from DISTUTILS_USE_SETUPTOOLS perspective, and ‘rdepend’ is no longer valid when when entry points are used.

I suppose that most of the Gentoo developers have seen at least one of the ‘uses a probably incorrect DISTUTILS_USE_SETUPTOOLS value’ bugs by now. Over 350 have been filed so far, and new ones are filed practically daily. The truth is, I’ve never intended for this QA check to result in bugs being filed against packages, and certainly not that many bugs.

This is not an important problem to be fixed immediately. The vast majority of Python packages depend on setuptools at build time (this is why the build-time dependency is the eclass’ default), and being able to unmerge setuptools is not a likely scenario. The underlying idea was that the QA check would make it easier to update DISTUTILS_USE_SETUPTOOLS when bumping packages.

Nobody has asked me for my opinion, and now we have hundreds of bugs that are not very helpful. In fact, the effort involved in going through all the bugmail, updating packages and closing the bugs greatly exceeds the negligible gain. Nevertheless, some people actually did it. I have bad news for them: setuptools upstream has changed entry point mechanism, and most of the values will have to change again. Let me elaborate on that.
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Gentoo Python Guide

Gentoo provides one of the best frameworks for providing Python support in packages among operating systems. This includes support for running multiple versions of Python (while most other distributions avoid going beyond simultaneous support for Python 2 and one version of Python 3), alternative implementations of Python, reliable tests, deep QA checks. While we aim to keep things simple, this is not always possible.

At the same time, the available documentation is limited and not always up-to-date. Both the built-in eclass documentation and Python project wiki page provide bits of documentation but they are mostly in reference form and not very suitable for beginners nor people who do not actively follow the developments within the ecosystem. This results in suboptimal ebuilds, improper dependencies, missing tests.

Gentoo Python Guide aims to fill the gap by providing a good, complete, by-topic (rather than reference-style) documentation for the ecosystem in Gentoo and the relevant eclasses. Combined with examples, it should help you write good ebuilds and solve common problems as simply as possible.

Gentoo Python Guide sources are available on GitHub. Suggestions and improvements are welcome.

No more PYTHON_TARGETS in single-r1

Since its inception in 2012, python-single-r1 has been haunting users with two sets of USE flags: PYTHON_TARGETS and PYTHON_SINGLE_TARGET. While this initially seemed a necessary part of the grand design, today I know we could have done better. Today this chymera is disappearing for real, and python-single-r1 are going to use PYTHON_SINGLE_TARGET flags only.

I would like to take this opportunity to explain why the eclass has been designed this way in the first place, and what has been done to change that.
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A better ebuild workflow with pure git and pkgcheck

Many developers today continue using repoman commit as their primary way of committing to Gentoo. While this tool was quite helpful, if not indispensable in times of CVS, today it’s a burden. The workflow using a single serial tool to check your packages and commit to them is not very efficient. Not only it wastes your time and slows you down — it discourages you from splitting your changes into more atomic commits.

Upon hearing the pkgcheck advocacy, many developers ask whether it can commit for you. It won’t do that, that’s not its purpose. Not only it’s waste of time to implement that — it would actually make it a worse tool. With its parallel engine pkgcheck really shines when dealing with multiple packages — forcing it to work on one package is a waste of its potential.

Rather than trying to proliferate your bad old habits, you should learn how to use git and pkgcheck efficiently. This post aims to give you a few advices.

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