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Using rules_jvm_external with bzlmod

Bzlmod is the new package manager for Bazel modules, included in Bazel 6.0. It allows a significantly shorter setup than the WORKSPACE file used prior to bzlmod.

Note: this support is new as of early 2023, so expect some brokenness and missing features. Please do file issues for missing bzlmod support.

See the /examples/bzlmod folder in this repository for a complete, tested example.

Installation

First, you must enable bzlmod. Note, the Bazel team plans to enable it by default starting in version 7.0. The simplest way is by adding this line to your .bazelrc:

common --enable_bzlmod

Now, create a MODULE.bazel file in the root of your workspace, setting the version to the latest one available on https://registry.bazel.build/modules/rules_jvm_external:

bazel_dep(name = "rules_jvm_external", version = "...")
maven = use_extension("@rules_jvm_external//:extensions.bzl", "maven")
maven.install(
    artifacts = [
        # This line is an example coordinate, you'd copy-paste your actual dependencies here
        # from your build.gradle or pom.xml file.
        "org.seleniumhq.selenium:selenium-java:4.4.0",
    ],
)
use_repo(maven, "maven")

Now you can run the @maven//:pin program to create a JSON lockfile of the transitive dependencies, in a format that rules_jvm_external can use later. You'll check this file into the repository.

$ bazel run @maven//:pin

Ignore the instructions printed at the end of the output from this command, as they aren't updated for bzlmod yet. See #836

Due to #835 this creates a file with a longer name than it should, so we rename it:

$ mv rules_jvm_external~4.5~maven~maven_install.json maven_install.json

Now that this file exists, we can update the MODULE.bazel to reflect that we pinned the dependencies.

Add a lock_file attribute to the maven.install() call like so:

maven.install(
    ...
    lock_file = "//:maven_install.json",
)

Finally, update the use_repo call to also expose the unpinned_maven repository used to update the dependencies:

use_repo(maven, "maven", "unpinned_maven")

Now you'll be able to use the same @unpinned_maven//:pin operation described in the workspace instructions.

Artifact exclusion

The non-bzlmod instructions for how to configure exclusions from the README don't work as shown for bzlmod; it's not possible to "inline" them as shown (it will cause an ERROR: in tag at <root>/MODULE.bazel:22:14, error converting value for attribute artifacts: expected value of type 'string' for element 9 of artifacts, but got None (NoneType)). Split it like this instead:

# https://github.com/grpc/grpc-java/issues/10576
maven.artifact(
    artifact = "grpc-core",
    exclusions = ["io.grpc:grpc-util"],
    group = "io.grpc",
    version = "1.58.0",  # Keep version in sync with below!
)
maven.install(
    artifacts = [
        "junit:junit:4.13.2",
        ...

Known issues

  • Some error messages print instructions that don't apply under bzlmod, e.g. #827
  • Java Gazelle extension isn't available