bazel-deps

Generate bazel dependencies transitively for maven artifacts, with scala support.

Usage

First, list all of your maven artifact dependencies in a Dependencies file.

Next, run parseproject on your project yaml file. This will create a tree of BUILD files that match the maven group id, and the artifact id will be a label in a BUILD file. You should not edit these by hand, and instead have a separate directory for any exceptions that you manage along with Replacements. For instance, this project is setup with:

bazel run //:parse -- generate -r `pwd` -s 3rdparty/workspace.bzl -d dependencies.yaml

We give three arguments: the path to the file we will include in our workspace. The path to the root of our bazel repo. The path to the dependencies file. You can also run with --help.

Then you should add

load("//3rdparty:workspace.bzl", "maven_dependencies")

maven_dependencies()

to your workspace to load the maven dependencies.

For example, if your project is located at MY_PROJ_DIR, your dependencies file is at MY_PROJ_DIR/dependencies.yaml, and your checkout of bazel-deps is at BAZEL_DEPS, to generate the dependencies you need to do the following:

cd $BAZEL_DEPS
bazel run //:parse generate -- --repo-root "$MY_PROJ_DIR" --sha-file 3rdparty/workspace.bzl --deps dependencies.yaml

The final result in MY_PROJ_DIR will look like this

MY_PROJ_DIR
├── 3rdparty             <-- everything under here is generated by running gen_maven_deps.sh
│   ├── workspace.bzl        <-- load() this from main WORKSPACE
│   └── jvm/                 <-- generated BUILD files in this directory.
├── BUILD
├── WORKSPACE
└── dependencies.yaml    <-- your project's dependencies are declared in here.

Whenever you update the dependencies declared in dependencies.yaml you will need to regenerate the contents of the 3rdparty directory by re-running $BAZEL_DEPS/gen_maven_deps.sh generate.

Alternate outputs, external repo

Bazel-deps can also prepare the outputs, not as a file tree but an external repo. With this one would refer to targets as @third_party//foo:bar rather than //3rdparty/jvm/foo/bar. This is useful if you do not want to check in generated code to your repo. Also if multiple repos are depending upon one another and using bazel deps this can avoid broken transitive dependencies. That is if there are two repos A and B where B depends on A: where A has Foo 1.0 dependson Jackson27 and B has Foo 2.0 depends on circe with the checked in version both will compile from source against the local copy of Foo, but transitively on the classpath in the repo B Jackson27 will be on the classpath rather than circe.

To use this option you would execute bazel-deps like:

cd $BAZEL_DEPS
bazel run //:parse generate -- --repo-root "$MY_PROJ_DIR" --sha-file 3rdparty/workspace.bzl --deps dependencies.yaml --target-file 3rdparty/target_file.bzl --disable-3rdparty-in-repo

In your dependencies.yaml file you will likely want: thirdPartyDirectory: "" to avoid prefixing the remote repo path with 3rdparty/jvm.

And finally to load it from your WORKSPACE you would use:

load("//3rdparty:target_file.bzl", "build_external_workspace")

build_external_workspace(name = "third_party")

Assumptions and usage

This tool will generate one canonical version for every jar in the transitive dependencies of the root dependencies declared. You have three conflict resolution modes currently (which currently apply globally):

• fail: if more than one version is found transitively, fail.
• fixed: for all artifacts explicitly added, use that version, otherwise fail if any other artifact has multiple versions.
• highest: for all artifacts explicitly added, use that version, otherwise take the highest version.

In any case, we add a comment for any duplicates found in the workspace loading file.

To declare dependencies, add items to the dependencies key in your yaml file. The format should be yaml or json. It should have dependencies and it may have replacements and options. Important: only dependencies explicitly named have public visibility, transitive dependencies not listed in the dependencies file have visibility limited to the third party directory.

Dependencies

Dependencies are a map from maven group id to artifact id, with some metadata, such as:

dependencies:
  com.google.guava:
    guava:
      version: "18.0"
      lang: java

Language is always required and may be one of java, scala, scala/unmangled. To control the scala version, see the Options section. A common case are projects with many modules. For instance in the scalding project there are many modules: -core, -date, -args, -db, -avro to name a few. To reduce duplication you can do:

dependencies:
  com.twitter:
    scalding:
      version: 0.16.0
      lang: scala
      modules: [core, date, args, db, arvo]

The version field is optional. If it is absent, it means this jar is expected to be found by transitive dependencies, and it is available to be used outside of the thirdparty directory, but the exact version used can be selected according to the version resolution rules. It is an error to have an unversioned dependency that is not a transitive dependency of another versioned dependency.

A target may optionally add exports and exclude lists to a dependency. exports should be just the group and artifact (such as: com.twitter:scalding-core in the above), and they should be listed in the dependencies. exclude list should also be only the group and artifact.

It's possible to add generateNeverlink option to a dependency, which will make the generator to generate this dependency twice:

1. With the normalized name as usual.
2. With the name ${normalized}_neverlink and neverlink is set as true. This option should be used only for java dependencies, it will be ignored in any other lang.

Each group id can only appear once, so you should collocate dependencies by group. WARNING the parsing library we are using does not fail on duplicate keys, it just takes the last one, so watch out. It would be good to fix that, but writing a new yaml parser is out of scope.

Packaging and Classifiers

Depending on artifacts with classifiers is straightforward: just add the packaging and classifier as part of the artifact id:

dependencies:
  net.sf.json-lib:
    json-lib:jar:jdk15: # artifact:packaging:classifier
      lang: java
      version: "2.4"

Note: Currently, only jar packaging is supported for dependencies. More work is needed on the bazel-deps backend to ensure that non-jar dependencies are written as data attributes, instead of regular jar dependencies.

Excluding artifacts with packaging or classifiers is similar to including dependencies. Non-jar packaging is supported for exclude.

  com.amazonaws:
    DynamoDBLocal:
      lang: java
      version: "1.11.86"
      exclude:
        - "com.almworks.sqlite4java:sqlite4java-win32-x86:dll"
        - "com.almworks.sqlite4java:sqlite4java-win32-x64:dll"
        - "com.almworks.sqlite4java:libsqlite4java-osx:dylib"
        - "com.almworks.sqlite4java:libsqlite4java-linux-i386:so"
        - "com.almworks.sqlite4java:libsqlite4java-linux-amd64:so"

Annotation Processors (processorClasses)

A target may also optionally add processorClasses to a dependency. This is for annotation processors. bazel-deps will generate a java_library and a java_plugin for each annotation processor defined. For example, we can define Google's auto-value annotation processor via:

dependencies:
  com.google.auto.value:
    auto-value:
      version: "1.5"
      lang: java
      processorClasses: ["com.google.auto.value.processor.AutoValueProcessor"]

This will yield the following:

java_library(
    name = "auto_value",
    exported_plugins = [
        ":auto_value_plugin",
    ],
    visibility = [
        "//visibility:public",
    ],
    exports = [
        "//external:jar/com/google/auto/value/auto_value",
    ],
)

java_plugin(
    name = "auto_value_plugin",
    processor_class = "com.google.auto.value.processor.AutoValueProcessor",
    deps = [
        "//external:jar/com/google/auto/value/auto_value",
    ],
)

If there is only a single processorClasses defined, the java_plugin rule is named <java_library_name>_plugin. If there are multiple processorClasses defined, each one is named <java_library_name>_plugin_<processor_class_to_snake_case>.

Options

There are a number of ways to customize the generated build files. These are controlled by the options dictionary at the root-level of the dependencies file. This is a list of all of the supported options.

• buildHeader: usually you will want to configure your scala support here:

  buildHeader:
    - load("@io_bazel_rules_scala//scala:scala_import.bzl", "scala_import")

• languages: an array of languages to be supported either Java or a specific version of Scala, e.g. [ "java", "scala:2.12.8" ].
• thirdPartyDirectory: path to where we write the BUILD files for thirdparty. The default is 3rdparty/jvm. If you choose the Google default of third_party you will need to configure the licenses option as well.
• versionConflictPolicy: fixed, fail or highest
• transitivity: runtime_deps or exports
• resolvers: the maven servers to use. Each resolver is defined by three keys, an "id", a "type", and a "url".

  resolvers:
    - id: "mavencentral"
      type: "default"
      url: https://repo.maven.apache.org/maven2/
    - id: "myserver"
      type: "default"
      url: https://my.private.maven.server.com/mvn/

• resolverCache: (with resolverType: aether) where bazel-deps should cache resolved packages. local (target/local-repo in the repository root) or bazel_output_base (bazel-deps/local-repo inside the repository's Bazel output base -- from bazel info output_base). Coursier ignores this option and uses ~/.cache/coursier.
• namePrefix: a string added to the generated workspace names, to avoid conflicts. The external repository names and binding targets of each dependency are prefixed.
• strictVisibility: this is enabled by default, when enabled a target must be explicitly declared in the dependencies.yaml file or it will not be visible to the rest of the workspace. If it is set to false all targets will be generated with public visibility.
• licenses: a set of strings added a licenses rule to each generated bazel target. Required by bazel if your build targets are under third_party/. See the licenses function in Bazel.
• resolverType: aether or coursier. Note that aether is slower and seems to silently miss some dependencies for reasons we don't yet understand.
• buildFileName: filename of the generated build files

In the default case, with no options given, we use:

• allow java and scala 2.11
• 3rdparty/jvm as the thirdPartyDirectory.
• highest versionConflictPolicy
• exports transitivity
• use maven central as the resolver
• local resolverCache
• empty namePrefix ("")
• coursier resolverType
• BUILD as build file name

Replacements

Some maven jars should not be used and instead are replaced by internal targets. Here are some examples of this:

1. A subproject in the repo is published as a maven artifact (A). Others (B) depend on this artifact (B -> A) and in turn we depend on those (we have added B to our dependencies file). We don't want to pull A from a maven repo, since we build it internally, so we replace that artifact with an internal target.
2. We get some scala artifacts directly from the sdk. So, if a jar says it needs org.scala-lang:scala-library we already have that (and a few other jars) declared, and we don't want to risk having two potentially incompatible versions.
3. A small external project has both a bazel build and a maven publishing. We prefer to use the bazel build so we can easily pull more recent versions by bumping up a gitsha rather than waiting for jar to be published.

The replacements work on the level of artifacts. An artifact is replaced one-for-one with a local bazel target. For instance:

replacements:
  org.scala-lang:
    scala-library:
      lang: scala/unmangled # scala-library is not mangled like sbt does with other jars
      target: "@io_bazel_rules_scala_scala_library"
    scala-reflect:
      lang: scala/unmangled
      target: "@io_bazel_rules_scala_scala_reflect"

In this way, we redirect maven deps to those providers.

Note, we stop walking the graph when we see a replaced node, so the replacement target is now responsible for building correctly, and correctly exporting any dependencies that need to be on the compile classpath.

Code

This code was originally forked from pgr0ss/bazel-deps

This code was inspired by the aether examples for walking maven dependencies.