This documentation is for rule writers who are planning to make their rules available to others.
Hosting and naming rules
Repository names for Bazel rules are standardized on the following format:
Make sure to use a descriptive GitHub repository description and
- Repository: bazelbuild/rules_go
- Repository description: “Go rules for Bazel”
- Repository tags:
README.htmlheader: “Go rules for Bazel” (note the link to https://bazel.build which will guide users who are unfamiliar with Bazel to the right place)
Rules can be grouped either by language (e.g., Scala) or some notion of platform (e.g., Android.
Every rule repository should have a certain layout so that users can quickly understand new rules.
For example, suppose we are writing new rules for the (make-believe) mockascript language. We would have the following structure:
.travis.yml README.html WORKSPACE mockascript/ BUILD mockascript.bzl tests/ BUILD some_test.sh another_test.py examples/ BUILD bin.mocs lib.mocs test.mocs
At the top level, there should be a README.html that contains (at least) what
users will need to copy-paste into their WORKSPACE file to use your rule.
In general, this will be a
git_repository pointing to your GitHub repo and
a macro call that downloads/configures any tools your rule needs. For example,
for the Go
git_repository( name = "io_bazel_rules_go", remote = "https://github.com/bazelbuild/rules_go.git", tag = "0.0.2", ) load("@io_bazel_rules_go//go:def.bzl", "go_repositories") go_repositories()
If your rules depend on another repository’s rules, specify both in the
README.html (see the Skydoc rules,
which depend on the Sass rules, for an example of this).
There should be tests that verify that the rules are working as expected. This
can either be in the standard location for the language the rules are for or a
tests/ directory at the top level.
It is useful to users to have an
examples/ directory that shows users a couple
of basic ways that the rules can be used.
Set up Travis as described in their getting started
docs. Then add a
.travis.yml file to your repository with the following content:
# On trusty images, the Bazel apt repository can be used. addons: apt: sources: - sourceline: 'deb [arch=amd64] http://storage.googleapis.com/bazel-apt stable jdk1.8' key_url: 'https://bazel.build/bazel-release.pub.gpg' packages: - bazel script: - bazel build //... - bazel test //...
Right now Bazel has to be compiled from source, as Travis does not support a
version of GCC that works with the precompiled Bazel binaries. Thus, the
before_install steps download the Bazel source, compile it, and “install” the
Bazel binary in /usr/bin.
See the Skydoc documentation for instructions on how to comment your rules so that documentation can be generated automatically.
Why can’t we add our rule to the main Bazel GitHub repository?
We want to decouple rules from Bazel releases as much as possible. It’s clearer who owns individual rules, reducing the load on Bazel developers. For our users, decoupling makes it easier to modify, upgrade, downgrade, and replace rules. Contributing to rules can be lighter weight than contributing to Bazel - depending on the rules -, including full submit access to the corresponding GitHub repository. Getting submit access to Bazel itself is a much more involved process.
The downside is a more complicated one-time installation process for our users: they have to copy-paste a rule into their WORKSPACE file, as shown in the README section above.
We used to have all of the rules in the Bazel repository (under
//tools/build_defs). We still have a couple rules
there, but we are working on moving the remaining rules out.