Skip to content

bzlmod

Migrating to Bazel Modules (a.k.a. Bzlmod) - Fixing and Patching Breakages

In the previous Bzlmod post, we covered writing your own Bazel module extensions to adapt your own setup code for dependencies that aren't Bzlmod compatible. However, there are other Bzlmod incompatibilities and related breakages that module extensions alone can't fix, such as forbidden API usage or Windows path length errors.

This post shows you how to patch your dependencies and covers several situations where patching is the only solution. We'll describe how to create and apply patches for your dependencies, if you can't wait for upstream fixes (or contribute them yourself).

Migrating to Bazel Modules (a.k.a. Bzlmod) - Module Extensions

So far, we've covered relatively easy Bzlmod fixes, how to hold runfiles and pkg_tar correctly, and how to access canonical repo names when absolutely necessary. Now we'll discuss replacing WORKSPACE statements with your own module extensions. You can use them to wrap your project's setup macros, and to adapt external repositories that aren't Bzlmod compatible to work with your Bzlmodified project.

Migrating to Bazel Modules (a.k.a. Bzlmod) - Repo Names, Macros, and Variables

The previous two posts in this series showed how to use runfiles mechanisms and rules_pkg mechanisms to avoid dealing with canonical repository names under Bzlmod. However, one special case remains: when you need to depend on the name of a repository directory, either at build time or runtime. This post explains how to access canonical repository names in a portable way to solve such problems. We'll use a macro when we can, and a custom Make Variable when we can't, including when dealing with alias targets.

Migrating to Bazel Modules (a.k.a. Bzlmod) - Repo Names and rules_pkg

The previous post in our Bzlmod migration series demonstrated how to make runfiles paths portable to a Bzlmod world. Another common source of Bzlmod file path breakages are misconfigured rules from rules_pkg, which contains rules for building archives from build outputs and/or external repositories. This post will explain key details of some of these rules, so you can stop "holding it wrong" and easily migrate archive targets to Bzlmod.

Migrating to Bazel Modules (a.k.a. Bzlmod) - Repo Names and Runfiles

The first post in our Bzlmod migration series explained many of the problems that may arise when migrating your project. These next three posts will explore various solutions to problems arising from changes in how Bazel handles repository names under Bzlmod, beginning with runfiles paths. After applying the techniques in this post, your project should be well insulated from runfiles path related breakages, now and well into the future.

Migrating to Bazel Modules (a.k.a. Bzlmod) - The Easy Parts

You may be aware that Bazel will remove support for WORKSPACE in Bazel 9 in favor of Bazel Modules (a.k.a. Bzlmod). The current mainstream release is Bazel 7.2.0, so there's plenty of time to migrate. However, there's no time like the present to get started, to avoid further WORKSPACE dependencies and a pile of migration work in the future.

I recently completed the Bzlmod migration for EngFlow/example and our internal repos. This experience taught me a lot about Bzlmod and about migrating complex projects with challenging dependency issues that I'll share over a few blog posts. I'll also borrow from Sara Adams's earlier post, in which she described an example bzlmod migration based on EngFlow's Bazel Invocation Analyzer repo.