Android

Tech principles

To inform decision-making when writing and reviewing code use the principles documented in: mobile/android/fenix/docs/Tech-Principles.md

Workflow

• Instead of gradlew, use ./mach gradle as the wrapper. Use -p argument of gradle if you need to run in a subdirectory

Android Frontend

When working in mobile/android/fenix, mobile/android/focus-android or mobile/android/android-components directories override instructions from the top-level AGENTS.md with:

• ./mach lint is the recommended way to run linters and format code all in one go.
  • It is currently too slow to run in fast feedback loops. Run it only at the end of implementing a change (or a major piece of a bigger change), like when checking if it's ready to submit a patch.
  • In case you need a faster feedback loop, you can run a subset of fast linters with ./mach gradle ktfmtFormat detekt. It is not equivalent to ./mach lint and doesn't guarantee patch submission readiness.
  • Default to running code formatting as part of ./mach lint or with ./mach gradle ktfmtFormat. Don't run ./mach format in fenix/focus-android/android-components, because it skips android formatters.
• Run ./mach build only when new changes are pulled into the work tree, or if ./mach gradle ... commands do not succeed.
• Run ./mach gradle [fenix|focus|components:<component>]:assembleDebug when you want to verify subsequent Android frontend code changes.
• Don't run ./mach test with --auto, it doesn't work on Android frontend code changes. Instead, run it for a file/feature you're working on with:
  • ./mach test <file-name> to run all tests in the file
  • ./mach test <directory-name> to run all tests in the directory
  • ./mach test {fenix,focus,ac,android-components,geckoview} to run all tests in the specific project
• When adding the first Robolectric test (@RunWith(AndroidJUnit4::class)) to an android-components module:
  • Add testImplementation libs.robolectric to its build.gradle
  • Add src/test/resources/robolectric.properties with sdk=37. CI fetches the Robolectric jars only for modules with this file, so don't add it to modules without Robolectric tests.