It's been almost six years since the previous entry in this series was originally published, and there are many new topics to discuss!
The biggest change in the last few years was the introduction of Bazel modules (also known as Bzlmod) and the deprecation of WORKSPACE mode. I've updated all the previous articles to be compatible with Bazel modules, but today we'll explore newly introduced functionality: how to write a module extension, and why you'd want to do so.
This "Maintaining Compatibility" trilogy began by describing how to, well,
maintain compatibility with Bzlmod builds, legacy WORKSPACE builds, and a
range of dependency versions. However, this was only half the story. Automated
testing is essential for validating our compatibility assertions, not lying to
ourselves and our users, and preventing the undoing of our hard work.
The previous post described how to write and run tests
that enable switching between Bazel versions and the Bzlmod and legacy
WORKSPACE build modes. Those tests use the latest versions of our non-Bazel
dependencies to ensure forward compatibility.
This fourth and final part of our trilogy describes how to write tests to
validate backwards compatibility with combinations of older dependency
versions. We'll build on the techniques from the previous post, while learning
what makes these backwards compatibility tests substantially different from
other tests in the suite.
We've covered techniques for ensuring that your project remains compatible with
different Bazel versions, both Bzlmod and legacy WORKSPACE builds, and older
dependency versions. However, we shouldn't make any promises until we've
validated that these properties actually hold, preferably via automated testing
and continuous integration.
This third post in our four part trilogy covers writing Bazel tests that
allow for flexibly switching between various Bazel configurations. We'll
consider advice on how to run the tests locally while developing and how to run
them in continuous integration.
In the previous post, we reviewed guidelines for
maintaining compatibility with both Bzlmod and legacy WORKSPACE builds, and
older and newer dependency versions. I promised that in this post and the next,
we'd discuss testing approaches to help ensure that this remains the case.
However, a discussion in the Bazel Slack workspace has revealed a Bzlmod and
legacy WORKSPACE compatibilty issue I'd missed in the previous post. So in
this post, I'll discuss what to do with the class of legacy WORKSPACE
configuration macros that use Label with computed repository names.
As we'll see, this one issue alone ended up meriting a substantial post in
itself. We'll cover adding dependency attributes to repository rules, generating
.bzl files to resolve Labels, chaining together module extensions, and using
macros in generated BUILD files. The former two options are relatively
straightforward, but we cover the latter two options in case your use case
requires them.
Such legacy WORKSPACE macros commonly seem to pertain to toolchain
configuration, selecting repositories to instantiate based on user defined
parameters. So we'll use a small example project to illustrate these solutions
as they apply specifically to toolchain configuration.
Boston is my second favorite city, after New York, of course! More on why below. It was a 1.5 day trip to meet the Boston Bazel community on the way to NYC from another San Francisco visit. Given the short trip, I only got a chance to do a tiny watercolor - see the cultural notes. However, I’ve gone back to Boston during my family vacation in Cape Cod, so I have much more to share in the form of my daily watercolor inspiration from the various day trips we’ve done on the Cape!
As we're well aware by now, Bzlmod is the new hotness, and WORKSPACE is old and
busted and going away in Bazel 9. However, Bazel 8 still supports
WORKSPACE, and thus legacy WORKSPACE usage won't completely disappear for
some years yet. Despite the Bazel community's efforts to help facilitate Bzlmod
migrations (including this blog series), some projects may remain unable to
migrate sooner than later.
What's more, publishing your repository for use by other projects raises the
challenge of supporting a range of older and newer versions of its dependencies.
Your repository should work with the newest versions of Bazel, rules_java,
protobuf, and other dependencies in order to stay current. However, not every
project that could benefit from the latest version of your repository will want
to upgrade these other dependencies right away.
This post describes how to design a repository to remain compatible with both
WORKSPACE and Bzlmod, and with newer and older dependency versions. Just as
importantly, in the next two posts, we'll discuss testing approaches to help
ensure that this remains the case.
In May, we co-hosted the London Build Meetup with Tweag by Modus Create and Jane Street. Build system insights, stories about first-hand build challenges, and great conversations packed the afternoon and evening. The lineup covered everything from large-scale migration battles to new research. If you missed it, here’s what you need to know.
Part of the promise of Bazel modules is that they are largely self-initializing
in an order-independent way. Rule sets, in particular, no longer need to burden
users with importing and invoking macros to instantiate repositories and
toolchains in a specific order. This burden now shifts to rule set maintainers,
but the existing implementation may not provide this ease of use without
modification.
This post describes the introduction of a new "toolchainized" API for
rules_scala v7.0.0 that better encapsulates toolchain configurations and
dependencies. We'll see how this new design enables optimal Bzlmod
compatibility, while simultaneously shrinking the legacy WORKSPACE API surface
without losing functionality. We'll also see how the Bzlmod and legacy
WORKSPACE APIs provide similar interfaces while sharing the same underlying
implementation, facilitating Bzlmod migrations.
As a thank you for our customers’ incredible support, we launched the Customer Forest Initiative. Throughout the 2024 holiday season, we planted trees on behalf of our customers, as an expression of our gratitude. The Customer Forest represents shared progress and growing stronger together.
We wanted a gift that truly reflected the value of our partnerships and the impact we can achieve together. Planting trees was the perfect choice, symbolizing growth, connection, and our shared commitment to a better future with our customers.
Another successful build meetup done! Our April meetup was co-hosted by JetBrains. The night was all about swapping stories, learning something new, and enjoying some good food and drinks. If you missed out, read the recap below and check out meetup.build for the next one!
