Chromium Flag Ownership

ellyjones@ / avi@

This document explains flag ownership in Chromium, and gives some principles and best practices.

What Is Flag Ownership?

Every entry in chrome://flags is required to have at least one listed owner, which can be:

A single person
A mailing list
A reference to an OWNERS file

The owners of a flag serve as points of contact for it, and are notified when it expires.

Who Should Be An Owner?

In general, it's a good idea to include:

The one or two SWEs who know the most about the flag and why it exists
An appropriate mailing list for the team that owns it, so that expirations are not missed, or
An owners file that contains all the members of the owning team, again so that expirations are not missed.

Three important notes about listing owners:

Any entry that is just a bare word (like “username”) is treated as being @chromium.org; by far the most common mistake is to write “username” when “username@google.com” is meant. This is not a problem if you have both chromium.org and google.com addresses.
The flag ownership database is public, so if your team‘s name is supposed to be secret, don’t list it; in that situation, it‘s better to create a new list with a less revealing name and have it forward to your team’s list.
Every listed owner must be able to receive email from an unprivileged google.com account, so please don‘t list your team’s private list that requires joining to post or similar - your flag expiration email will bounce. If your team's list needs to remain closed to posting, you should instead make a separate list that allows open posting, or list an OWNERS file full of individuals.

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 at least 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 or later. However, you can freely leave yourself lots of slack - the purpose of expiration is to ensure that obsolete flags eventually get cleaned up, but whether that takes one milestone or five for any given flag is not a big deal. It is also very easy to adjust the expiration milestone later if you need to.

One practice is to always set your expirations to the next “round” milestone after you expect to launch, so that your team can batch flag cleanup work - for example, if your feature is planned to go out in M101, you might set the expiration to M105, and then your team might schedule a flag cleanup for the 105 branch time.

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@.