bazel-rust-mobile-demo

This is an example repository for how to setup a bazel build that uses rust on iOS and Android. I also did a talk on this at bazelcon.

Usage

You can explore the code, which has some comments around the issues you hit. You can also run each entry point to see them working.

For a standard cc_binary running on your host machine:

$ bazel run normal_binary
...
Ferris says hello!
Some value from rust: 42

For an ios_application (requires running on macOS with Xcode setup):

$ bazel run ios_app
...
com.example.iosapp: 25008
Ferris says hello!
Some value from rust: 42

For an android_application (requires the android SDK and an emulator to be configured):

$ bazel mobile-install android_app --fat_apk_cpu=arm64-v8a --start_app
# View the result in the emulator, or view logs with 'adb logcat'

At the time of writing this setup was tested with bazel 5.1.1
The key to targeting the right platforms until the iOS and Android rules natively support bazel platforms is the platform_mappings file, and the platform rules in the BUILD file (docs)
If you don't want to use a root platform_mappings file you can pass --platform_mappings=path/to/platform_mappings
The rules_rust patch, and android_armeabi platform definition will change with bazel 6.x since bazelbuild/bazel#14982 was fixed
When testing Android, depending on your emulator or device you can pass whatever --fat_apk_cpu value you need
When testing with iOS you can pass whatever --ios_multi_cpus value you need
When using something like this in production you should checkout cxx which helps bridge between rust and C++
This example doesn't include it but using cargo-raze works fine for rust dependencies from our testing
When using cargo-raze with the arm64 iOS simulator you need this patch for some cases, hopefully it's in a release soon
When debugging platform_mappings issues, --toolchain_resolution_debug='.*' is verbose but very useful
If you find any other interesting gotchas when setting this up please submit an issue or PR here so we can document them for the community!