Bazel compiles Java code using a custom builder. This builder is called JavaBuilder and its code lies in //src/java_tools/buildjar. To build Java code, JavaBuilder use the Java compiler from the JDK. To support ErrorProne checks, we vendor a custom build of the Java compiler code. This is the raw version of the Java compiler from OpenJDK but compiled for a lower version of the JRE. Those builds are vendored in //third_party/java/jdk/langtools.