Experimental Branches

flutter.dev/to/experimental-branches

Cocoon has experimental support for so-called experimental branches in the flutter/flutter repository.

An experimental branch might be used to test newer versions of an operating system, or make system-wide flag changes that are not yet in the state where they can land on master, but are too cumbersome to use something like led for due to how many steps are required.

WARNING: These branches are not officially supported, and if broken, are only considered a P2 (best effort) to fix.

Creating an experimental branch

Any branch on flutter/flutter that is not:

  • master
  • a release candidate, i.e. matches /flutter-\d+\.\d+-candidate\.\d+/
  • and supports PRs (i.e. excluding stable or beta, or similar)

... is an experimental branch.

To create an experimental branch, fork an existing branch (i.e. master), and update both //.ci.yaml and //engine/src/flutter/.ci.yaml so that the root enabled_targets: [ ... ] includes your branch title, and (recommended) remove targets not applicable to your experiment.

For an example, see https://github.com/flutter/flutter/pull/168860.

NOTE: New targets are not supported, that is, target names must exist already at tip-of-tree in the master branch.

Testing and Submitting PRs

PRs made against an experimental branch will work similar to the master channel:

  • If needed, the engine is built
  • Tests are run against the newly or previously built engine

Submitting a PR works similar to a release-candidate branch in that no merge queue is used.

Once a PR is submitted, it will show up on the Dashboard at a specific URL:

https://flutter-dashboard.appspot.com/#/build?repo=flutter&branch=<BRANCH_NAME>.

The engine is then built and uploaded to GCS, and every test is automatically marked as skipped.

Manually, tests can be scheduled against a sucessfully built engine. Either click the individual test, and hit “re-run”, or, for supported branches, use the “Run all tasks” feature to schedule every task for the commit to be run asynchronously (typically a few minutes, though may take longer when postsubmit queues are under load):

Example