A Java Toolchain for Bazel that uses ECJ (Eclipse Compiler for Java) for compilation.
The Eclipse Compiler for Java is much (much, much) faster than javac. It's even faster than Bazel's Java header compiler, i.e. with this toolchain you can disable Turbine header compilation and still have a faster build time. Additionally, we included a few optimizations to further improve the compilation performance. For example, it's possible to disable transitive dependencies and only compile with directly declared dependencies.
See releases for the release
specific notes and instructions what to add to your WORKSPACE file.
Once this is completed, add this to your .bazelrc:
build --extra_toolchains=@bazel_jdt_java_toolchain//jdt:all
By default the jdt_java_toolchain is using rules_java default for compilation.
Please create your own default_java_toolchain if this doesn't work for your use case.
Have a look at jdt/BUILD to see which JDKs are supported.
Read ECJ README for details about updating JDT.
Currently, there are some issues with clients that try to access use this toolchain by compiling the builder from source. Many of the Bazel macros depend on the current java toolchain, and because that toolchain has not been built yet, we run into a circular dependency.
The solution is for bazel-jdt-java-toolchain developers to build the toolchain and then
copy the deploy jar into the repository. Clients can then use the override_repository command
and point directly at the source of this repo for development and testing.
Unfortunately this means additional steps are required for developers. This script can be used to facilitate the steps.
#!/bin/bash
bazel build :JdtJavaBuilder_deploy.jar
cp -fv bazel-bin/JdtJavaBuilder_deploy.jar compiler/export/
bazel build //compiler/third_party/turbine:turbine_direct_binary_deploy.jar
cp -fv bazel-bin/compiler/third_party/turbine/turbine_direct_binary_deploy.jar compiler/tools/
For your convenience, the build-toolchain script is provided in this repository.
For debugging the toolchain's Java code (including ECJ compiler) here are a few notes:
Override repository in your project's .bazelrc (or via command line) and add debug statements as follows:
build --override_repository=jdt_java_toolchain=/Users/.../bazel-jdt-java-toolchain/
common --subcommands=pretty_print
common --verbose_failures
This will give output during the build how Bazel is invoking JDT compiler:
bazel build //some-java-target:target
INFO: Analyzed target //some-java-target:target (...).
INFO: Found 1 target...
SUBCOMMAND: # //ome-java-target:target [action 'Building some-java-target/libtarget-class.jar ...]
(cd /private/var/tmp/_bazel_username/hash/execroot/core && \
exec env - \
LC_CTYPE=en_US.UTF-8 \
LD_LIBRARY_PATH='' \
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin \
/Users/username/tools/Darwin/jdk/bin/java \
-jar \
external/jdt_java_toolchain/builder/export/JdtJavaBuilder_deploy.jar \
@bazel-out/darwin-fastbuild/bin/some-java-target/libtarget-class.jar-0.params \
@bazel-out/darwin-fastbuild/bin/some-java-target/libtarget-class.jar-1.params)
ERROR: /Users/username/app/main/core/some-java-target/BUILD.bazel:4:13: Building some-java-target/libtarget-class.jar ... failed: (Exit 1): java failed: error executing command
(cd /private/var/tmp/_bazel_username/hash/execroot/core && \
exec env - \
LC_CTYPE=en_US.UTF-8 \
LD_LIBRARY_PATH='' \
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin \
/Users/username/tools/Darwin/jdk/bin/java -jar external/jdt_java_toolchain/builder/export/JdtJavaBuilder_deploy.jar @bazel-out/darwin-fastbuild/bin/some-java-target/libtarget-class.jar-0.params @bazel-out/darwin-fastbuild/bin/some-java-target/libtarget-class.jar-1.params)
Either take the SUBCOMMAND or ERROR command.
You can ignore the exec env part.
The interesting two steps are:
cd /private/var/tmp/_bazel_username/hash/execroot/core
/Users/username/tools/Darwin/jdk/bin/java -jar external/jdt_java_toolchain/builder/export/JdtJavaBuilder_deploy.jar @bazel-out/darwin-fastbuild/bin/some-java-target/libtarget-class.jar-0.params @bazel-out/darwin-fastbuild/bin/some-java-target/libtarget-class.jar-1.params
The first is the execution directory and the latter the command.
You need to cd into the execution directory and then run the command yourself.
But this time add the remote debug arguments (before -jar) as follows:
/Users/username/tools/Darwin/jdk/bin/java -agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=8000 -jar external/jdt_java_toolchain/builder/export/JdtJavaBuilder_deploy.jar @bazel-out/darwin-fastbuild/bin/some-java-target/libtarget-class.jar-0.params @bazel-out/darwin-fastbuild/bin/some-java-target/libtarget-class.jar-1.params
The important part is suspend=y.
Without it the compiler would be finished before you are able to connect.
Once you run the command, connect to the waiting process with your IDE's remote debugger.
This project can be loaded with the Bazel Eclipse Feature. The VS Code Bazel Java extension should also work.
See RELEASING README.
