Shaka Player Maintenance Process

These are project-specific processes in addition to the general maintenance process documentation.

Release Branches

Feature release are made from the main branch. Any time that happens, our release automation will automatically create a release branch. So, for example, when v4.1.0 was released from main, a branch named v4.1.x was automatically created.

Future bug fixes would be cherry-picked from main to v4.1.x to create the releases v4.1.1, v4.1.2, etc., and the branch would become more stable over time.

Cherry-Picking

Features are never cherry-picked to a release branch. This would go against semantic versioning, which says that a patch-level release (third digit) can only contain backward-compatible bug fixes. Features scoped to test infrastructure or the demo app are an exception, since those are not part of the library itself.

Interactive Cherry-Pick Tool

We use a custom tool to perform an interactive cherry-pick. This is similar to the interactive rebase of git. When you run the tool, your default editor opens with a list of commits you may want to cherry-pick. Any commits left in the file when you quit the editor are cherry-picked using git.

If a commit fails to cherry-pick, the maintainer is given an error message from git and must either fix the conflict or instruct git to skip the commit.

Cherry-picks can be done 1 or more times between bug-fix releases. The release is finally made by merging the release PR for the branch.

For example, after installing the tool:

# Go to the Shaka Player repo.
cd /path/to/shaka-player

# Check out a release branch tracking the _upstream_ repo:
git checkout -b v3.3.x upstream/v3.3.x
# Or if you already have such a branch locally:
git checkout v3.3.x

# Inspect all commits since a particular main-branch tag.
# If the most recent v3.3.x release was v3.3.1, the tag
# v3.3.1-main is the same point in history for the main branch.
interactive-cherry-pick v3.3.1-main

# If you don't use the recommended "upstream" remote name,
# you can specify the name of your remote.  For example,
# if you named the shaka-project/shaka-player remote "google",
# you could run this to cherry-pick from that specific remote:
interactive-cherry-pick v3.3.1-main google

Pre-work:

1. Install the interactive cherry-pick tool: https://github.com/shaka-project/shaka-github-tools/tree/main/interactive-cherry-pick#installation
2. Create a local branch in Shaka Player tracking an upstream release branch

Cherry-picking:

1. Cherry-pick the necessary changes skipping all feature commits (see also "What to Pick" below)

   NOTE: If you aren't sure about a commit, you can select it now and change your mind later if there are merge conflicts and/or test failures

2. Fix any merge conflicts that come up, or choose to skip the current commit with git cherry-pick --skip

3. Run the compiler with python build/all.py

4. Run the tests with python build/test.py

5. If any tests fail, make the necessary changes to fix the cherry-picked commit that caused the failure (either to amend the earlier commits, or as a new commit on top)

6. When the build and all tests pass, push the cherry-picked commits upstream with git push

What to Pick

• Most bug fixes are cherry-picked to active release branches.
• Some bug fixes won't apply to a branch because they deal with features not present in that branch.
• Some bug fixes won't apply to a branch because the code in the branch is too different, in which case a decision must be made about whether porting the fix to the branch is worth the effort. The maintainer will have to consider both the severity of the issue and the difficulty of fixing conflicts or reimplementation.
  • If a conflict is trivial to resolve, or if there are no conflicts in a commit, the commit may be pushed directly to the release branch.
  • If reimplementation of a commit is required, please submit a PR to the branch instead of pushing directly.
• Non-code changes (docs, tests, demo, etc) are sometimes cherry-picked to branches, depending on what the change is and whether it makes sense for that branch.
• Features are never cherry-picked to release branches, as this would break semantic versioning.

Release Policy

Maintainers can make a feature release at almost any time. There is no need to wait to batch up any particular number of changes or any particular significant features.

Chromecast app IDs for feature releases

As long as we have our own Cast communication in Shaka Player (see https://github.com/shaka-project/shaka-player/issues/4214 for plans to change this), each feature release branch needs its own Cast receiver app registered. The newly registered ID must be put in demo/index.html and docs/tutorials/ui.md (search data-shaka-player-cast-receiver-id and castReceiverAppId).

The registration must currently be done by Google. It is acceptable for a non-Google maintainer to make a feature release, then ask the team at Google to follow up with an updated receiver ID in a .1 release afterward. The impact will only be to the demo app and documentation.

Testing PRs and Releases

PRs can now easily be tested in the lab by sending commands to @shaka-bot. For example, any maintainer may comment on a PR with @shaka-bot test to trigger a full test run in the lab. This command is not available to non-maintainers.

All release PRs should be tested in the lab prior to merging them.

A full set of commands can be found by commenting @shaka-bot help on any PR.

These commands and handled by the workflow in .github/workflows/talk-to-shaka-bot.yaml, and the implementation is in .github/workflows/shaka-bot-commands/.

Branch Maintenance Policy

We will cherry-pick bug fixes to LTS branches, plus the most recent 2 release branches.

There are two kinds of branches we will dub LTS:

• The last feature release (minor release number) before a breaking release (major release number) will receive fixes for 1 year
  • For example, v3.3 (right before v4.0) will be fixed for 1 year past the release of v4.0.0 (until April 30, 2023).
• The release currently used by the Cast Application Framework will continue to receive fixes until CAF upgrades to a newer Shaka Player release by default
  • As of June, 2022, this is currently v3.2.
  • Cherry-picking for any CAF-specific branch is the responsibility of the team at Google, rather than non-Google maintainers.

In addition to LTS branches, the most recent two branches will always receive fixes. If the most recent release branch is v4.1, the most recent two branches would be v4.1 and v4.0. After v4.2 is released, the most recent two branches would become v4.2 and v4.1. Unless v4.0 was the current CAF branch, we would stop fixing v4.0 when v4.2 is released.

To see current branch maintenance status, refer to maintained-branches.md in Shaka Player.

When to Make Breaking Changes

We should make breaking changes infrequently if we can. The goal should be one breaking release per year at most. If changes can be made in a backward-compatible way (with a shim or behind a non-default configuration), they should be. Then they can be released in a normal feature release.

Deprecated features, shims, and temporary configurations can be removed when a major (breaking) release is finally made.

For example, in v4.0, we were forced to make a change that disabled HLS support for older smart TVs. In that same release, we removed deprecated methods, configurations that were added to maintain compatibility with older releases, etc. Many of them had been marked deprecated for 6-12 months already.

Breaking changes need to be listed in docs/tutorials/upgrade.md, with details on what application developers will need to do to cope with each change.

Internal Release Processes

After making public releases, the following internal steps are taken at Google to make the release available in our internal systems. Detailed documents on these processes are internal-only (go/shaka-player).

1. Update the Chromecast receiver app URLs for the Shaka Player Demo

   TODO: Create subdomains in appspot that point to the latest release for a branch, to eliminate the need to update receiver app URLs.

2. Update Google3 (internal source repo)

   TODO: Automate this?

3. Update Google Hosted Libraries

   TODO: Automate this?

History

Before v3.0, we didn't strictly follow semantic versioning.

We would sometimes deprecate functionality (strictly speaking, a breaking change) without bumping the major version. App developers would get one feature release with backward compatibility and a warning log before we removed or changed part of the API in a breaking way.

We would also sometimes cherry-pick minor, backward compatible features to release branches to get those out more quickly.

Since v3.0, we have stopped these practices and followed semantic versioning strictly.

Screenshot Tests

Screenshot tests create some pre-defined layout, take a screenshot of it, and compare that screenshot to an accepted version stored in the repo. Debugging failures in such tests and updating those screenshots requires some explanation.

Screenshot Organization

All screenshots live in test/test/assets/screenshots/ in the repo. Each browser/platform combo gets its own subfolder, e.g. firefox-Windows/.

Within that, the accepted screenshot stored in the repo has a name constructed of the name of the test suite, whether native text or UI text rendering is used, and the name of the test case. For example, text-displayer-ui-basic-cue.png.

New screenshots are written to a related filename suffixed with -new, e.g. text-displayer-ui-basic-cue.png-new. A "diff" image highlighting the differences between the accepted and new versions is written to a filename suffixed with -diff, e.g. text-displayer-ui-basic-cue.png-diff. Neither of these files is stored in the repo. They are only temporary outputs of the test process, and are ignored by .gitignore.

Reviewing Screenshots

A built-in tool in the repo allows the review of screenshots and their changes. If your local Shaka Player demo is hosted at http://localhost/shaka/demo/, the screenshot review tool is hosted at http://localhost/shaka/test/test/assets/screenshots/review.html.

The top of the tool shows many filters you can apply to review only a subset of browser/platform combos, suites, native vs UI rendering, or specific test cases. The screenshot tiles below will be automatically hidden/shown based on your filters, and your filters modify the URL hash so that you can easily reload without losing state.

When you mouse over a tile, you see the accepted version of the screenshot only. If you hold down the shift key, you will see the new version. If you hold down the control key, you will see the diff image, highlighting changed areas in red.

Getting Screenshots From Lab Tests

The screenshot tests run nightly in the test lab, and screenshots are taken and saved on all platforms where we have that capability.

To review screenshot test failures from the nightly lab tests, go to the "Selenium Lab Tests" section of GitHub Actions and select the failed test run. At the bottom of the test run page, under the heading "Artifacts", you will see a number of artifacts whose name starts with screenshots-, e.g. screenshots-FirefoxWindows. Download each of those you wish to review.

Next go to your local Shaka Player source, and unpack these zip files from GitHub into test/test/assets/screenshots/. On Linux, it looks something like this:

cd /path/to/shaka-player/
cd test/test/assets/screenshots/
unzip -o ~/Downloads/screenshots-FirefoxWindows.zip
rm ~/Downloads/screenshots-FirefoxWindows.zip

After unpacking the zip files into your source directory, you now have the -new and -diff images from those platforms in our lab. You can reload the review tool and review those changes/failures.

Updating Screenshots

There are several cases where we need to update screenshots in the repo:

1. After fixing bugs and generating new screenshots to reflect those fixes
2. After browser/platform updates that significantly change rendering/layout
3. After creating new screenshot test cases

Though you can update screenshots with those generated by your local browsers, you should always run screenshot PRs through the "Selenium Lab Tests" action to get a complete set of updated screenshots for all supported platforms. (See "Getting Screenshots From Lab Tests" above.)

The process for updating screenshots is:

1. Run your PR (if any) through the "Selenium Lab Tests" action, or select a nightly run from main (see above)
2. Download updated screenshots for all platforms with failures (see above)
3. Review all screenshot changes in the review tool to make sure they are good changes we want to keep
4. Run python build/updateScreenshots.py to find changed screenshots and rename .png-new files to .png
5. Run git add on the updated screenshots
6. Incorporate those screenshots into your existing PR, or create a new one

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