shorebird-updater/UPDATING_ENGINE.md

Shorebird currently maintains patches to the Flutter Engine to integrate the Shorebird updater library.

We have changes to both flutter/engine and flutter/buildroot. We need to make sure those changes are applied to the correct version of each, to be compatible with a given flutter/flutter version.

• flutter/flutter version is whatever is the latest stable in flutter/flutter.
• From that you can get the flutter/engine version in bin/internal/engine.version in flutter/flutter.
• From that you can get the flutter/buildroot version in DEPS in flutter/engine

Working from a flutter/engine checkout can be confusing because the layout is: src/ <- flutter/buildroot src/flutter <- flutter/engine

gclient uses the file in src/flutter/DEPS to control the whole checkout, as directed by your .gclient file in the parent directory of src.

Here are the steps to update those forks every time Flutter releases:

1. You need the release name / git id for the Flutter release. e.g. 3.7.7
2. Fetch flutter at that tag
3. Look at engine version https://github.com/flutter/flutter/blob/3.7.7/bin/internal/engine.version See that is 1837b5be5f0f1376a1ccf383950e83a80177fb4e.
4. Rebase our engine patches onto that engine version. https://github.com/shorebirdtech/engine/tree/stable_codepush If the engine is tagged correctly (it isn't always) it's as simple as: `git rebase --onto 3.7.7 3.7.6
5. Should then also look at DEPS file in engine: https://github.com/flutter/engine/blob/3.7.7/DEPS Where we are looking for the buildroot hash: https://github.com/flutter/engine/blob/3.7.7/DEPS#L239
6. We now need to rebase the buildroot (src/) changes onto the buildroot version in that DEPS. https://github.com/shorebirdtech/buildroot/tree/stable_codepush e.g. git rebase --onto 8747bce41d0dc6d9dc45c4d1b46d2100bb9ee688 93f7f85422a8604bdc44ef76c3f105ead65e8c1c Where as that should be --onto new_base_revision previous_base_revision. The base revision is the git id before we started making changes.
7. Once you've successfully rebased the buildroot, you then need to change the buildroot id in our fork of the engine (so that when others use gclient sync it pulls our modified buildroot rather than an unmodified one.
8. Finally, update the Shorebird CLI flutterEngineRevision to the new Flutter engine revision