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NOTE: This project is deprecated and no longer maintained.

BUILD File Generator

BUILD File Generator generates Bazel BUILD files for Java code.

  1. It reads all .java files, and extracts the class dependency graph.
  2. Computes the strongly connected components of the graph.
  3. For each component, creates a java_library rule.

Why is it useful?

Having all sources in a single BUILD rule doesn't allow Bazel to parallelize and cache builds. In order to fully benefit from Bazel, one must write multiple BUILD rules and connect them.

This project automates writing granular BUILD rules that allow Bazel to parallelize and cache builds.

It's useful to quickly try out Bazel on your project as well as to periodically optimize your build graph.

BFG is composed of two general components

  1. Language specific parsers
  2. The BFG binary

The parsers read your source code and generate a class dependency graph in the form of a protobuf. To generate your BUILD files, you pass the generated protobuf into the BFG binary.

Step 1: Using parsers to generate dependency graphs

Suppose your project's Java code is in core/src/main/java/ and core/src/test/java/.

bazel run //lang/java/src/main/java/com/google/devtools/build/bfg:JavaSourceFileParserCli -- --roots=core/src/main/java,core/src/test/java $(find core/src/main/java/ core/src/test/java/ -name \*.java) > bfg.bin

The output is a serialized [ParserOutput] (

) proto

Step 2: Generating BUILD files using BFG binary

TODO(bazel-devel): add explanation and valid example arguments.

bazel run //src/main/java/com/google/devtools/build/bfg -- --buildozer=$BUILDOZER --whitelist=$YOUR_JAVA_PACKAGE < bfg.bin

Supported Languages

We currently support Java projects. The next language on our roadmap is Scala.


Third-party Maven dependencies

We use a bazel-deps to manage Maven jar dependencies. All of our dependencies are listed in maven_deps.yaml. bazel-deps provides tools to manage dependencies in that file and generates the Bazel build files for them in thirdparty/jvm/.

To use bazel-deps, use the wrapper scripts in dev-scripts/dependencies/. Don't edit the files under thirdparty/jvm/ by hand.

To add or update a dependency, run ./dev-scripts/dependencies/ MAVEN_COORD, where MAVEN_COORD is the Maven coordinate of the dependency, such as Add the --scala option if it is a Scala dependency.

After running this, you'll see changes to maven_deps.yaml and one or more files under thirdparty/jvm. Add and commit all of those changes. Similarly, if you run with a new version of an existing dependency, it will be updated in maven_deps.yaml and any changed indirect dependencies will be reflected in the generated files.

You can also edit maven_deps.yaml manually. You will need to do this to remove a dependency, or to add exclusions to a dependency's dependencies. After making changes, run ./dev-scripts/dependencies/ to rebuild the generated files, and commit the changes to the generated files.