How to contribute

We'd love to accept your patches and contributions to this project. There are just a few small guidelines you need to follow.

Contributor License Agreement

Contributions to any Google project must be accompanied by a Contributor License Agreement. This is necessary because you own the copyright to your changes, even after your contribution becomes part of this project. So this agreement simply gives us permission to use and redistribute your contributions as part of the project. Head over to to see your current agreements on file or to sign a new one.

You generally only need to submit a CLA once, so if you‘ve already submitted one (even if it was for a different project), you probably don’t need to do it again.

Code reviews

All submissions, including submissions by project members, require review. We use GitHub pull requests for this purpose. Consult GitHub Help for more information on using pull requests.

Building Dagger

Dagger is built with bazel.

Ensure that Dagger is checked out on a case-sensitive filesystem. On a case-insensitive file system (e.g. Windows or MacOS by default) some tasks that attempt to delete the build/ folder will also delete the bazel BUILD files.

Building Dagger from the command line

  • Install Bazel
  • Build the Dagger project with bazel build <target>
    • Learn more about Bazel targets here.
    • Building Dagger's Android targets requires additional setup:
      • Set the ANDROID_HOME environment variable to point to a directory containing the Android SDK. If you do not have the Android SDK installed, you'll have to download and unzip it first.
      • Install the necessary components. For example, under Linux, run: $ANDROID_HOME/tools/bin/sdkmanager "platforms;android-32" "build-tools;32.0.0"
        • If you skip this step, you will see an error similar to ERROR: missing input file '@androidsdk//:build-tools/32.0.0/aapt'.
        • You may also need to run bazel sync.
  • Run tests with bazel test <target>, or bazel test //... to run all tests.
  • You can install the Dagger libraries in your local maven repository by running the ./util/ script.
    • It will build the libraries and install them with a LOCAL-SNAPSHOT version.

Importing the Dagger project in IntelliJ/Android Studio

  • Visit Preferences > Plugins in the IDE menu.
    • Search for bazel and install the plugin.
    • If no result shows up, click on Search in repositories, search for bazel and install the plugin.
  • Select Import Bazel Project.
  • Input the path to the Dagger project under workspace, click Next.
  • Select Generate from BUILD file, type BUILD in the Build file input, click Next.
  • [Android Studio only] In the Project View form, uncomment one of the android_sdk_platform lines. Pick one that you have installed, then click Finish.
  • If you get an error on Bazel sync, Cannot run program "bazel", then:
    • In the command line, run where bazel and copy the output (e.g. /usr/local/bin/bazel)
    • In Android Studio, go to Preferences > Bazel Settings and replace Bazel binary location with what you just copied.
  • Note that the first sync can take a long time. When build files are changed, you can run partial syncs (which should be faster) from the file menu.
  • [Android Studio only] To view the Dagger project structure, open the Project view and switch the top selector from Android to Project.