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Chrome Flag Ownership

ellyjones@ / avi@

[TOC]

TL;DR / What Do I Need To Do?

Look through chrome/browser/flag-metadata.json for flags that your team added, maintains, or cares about. For each such flag you find, either:

  • If it is still in use: add entries to the owners list (see the comment at the top of the file) and set an appropriate expiration milestone;

  • If it is not in use: delete it from kFeatureEntries in chrome/browser/about_flags.cc or ios/chrome/browser/about_flags.mm for iOS. Remember to file a cleanup bug to remove code paths that become dead. It is not necessary to delete the corresponding entry in flag-metadata.json as it will be cleaned up for you in the future.

Wait, What Are You Doing?

Presently, Chrome has approximately 600 entries in chrome://flags, many of which are obsolete and unused, but each of which represents configuration surface that is exposed to users and to QA. Worse, obsolete flags often prevent removal of legacy code paths that are not used in the field but are still reachable via a flag setting.

To deal with that, we are moving Chrome towards a model where chrome://flags entries are what they were originally intended to be: temporary, experimental options. Each flag must have a set owner who can keep track of whether or when that flag should expire and an express time by which it will expire, either because the feature it controls will have become default-enabled or because the feature it controls will have been cancelled.

Note that this change only affects chrome://flags entries, not features controlled via FeatureList (commonly used to run Finch trials) or command-line switches.

I Don't Want My Flag To Expire!

Some flags do not control UI features, but rather are commonly-used debugging controls, such as ignore-gpu-blocklist. For these flags, see the instructions at the head of flag-metadata.json. Please be very judicious about never-expiring flags, since they represent ongoing engineering, test and support burden. The flags team will probably only approve your non-expiring flag if:

  • You regularly ask users or developers to change its value for debugging/support purposes
  • You have been doing so for at least six months
  • You don't plan to stop doing so any time soon

If you have a non-expiring flag, the flags team requires a comment in the json file as to the rationale that it be non-expiring. A quick sentence or two will be fine. Yes, we are aware that, technically, JSON files can't have comments. Don't worry about it. You'll also need to add your flag to the permitted list in chrome/browser/flag-never-expire-list.json which will require approval from the flags team.

What Should My Expiry Be?

A good rule of thumb is that your flag should expire one milestone after you expect your feature to have launched to stable. In other words, if your feature will be 100% enabled on Stable in M74, your flag should be marked as expiring in M75.

Please do not stress about the expiration date. The purpose of the expiration milestone is to let us remove abandoned flags. Pick a reasonable milestone by which you'll be done with the flag; you can always adjust it later if your schedule changes.

I Have Other Questions

Please get in touch with flags-dev@chromium.org. If you feel like you need to have a Google-internal discussion for some reason, there's also chrome-flags@.