ellyjones@ / avi@
This document outlines the process by which flags in Chromium expire and are removed from the codebase. This document only describes entries in chrome://flags, not command-line switches (commonly also called command-line flags). This process does not cover command-line switches and there continue to be no guarantees about those.
See also Chromium Flag Ownership.
If you are a user or administrator of Chrome and are using (or think you need to use) a flag to configure Chromium for your use case, please file a bug or email flags-dev@, because that flag will likely be removed at some point. If you are a Chromium developer, please carry on using flags as normal :)
Flags have never been a supported configuration surface in Chromium, and we have never guaranteed that any specific flag will behave consistently or even continue to exist. This document describes a process for removing flags that have been around for long enough that users might have come to rely on their ongoing existence in a way that hopefully minimizes pain, but Chromium developers are free to change the behavior of or remove flags at any time. In particular, just because a flag will expire through this process does not mean a developer will not remove it earlier than this process specifies.
The logic in //tools/flags/generate_unexpire_flags.py implements most of this. At any given time, if the current value of MAJOR in //chrome/VERSION is $MSTONE, the two previous milestones ($MSTONE-1 and $MSTONE-2) are considered recent.
Then:
$MSTONE or higher are not expired$MSTONE-3 or lower are unconditionally expired$MSTONE-1 or $MSTONE-2 are expired by default, but can be temporarily unexpired via flags named “temporary-unexpire-flags-M$MSTONE”.There are other elements of this process not described here, such as emails to flags-dev@ tracking the status of the process.
Google employees: See more at go/flags-expiry-process and go/chrome-flags:expiry-process.
If a flag is no longer used (for instance, it was used to control a feature that has since launched), the flag should be removed. Delete the entry in //chrome/browser/about_flags.cc or //ios/chrome/browser/flags/about_flags.mm for iOS (and any corresponding entries for the flag description), and remove any references in //chrome/browser/flag-metadata.json.
https://crbug.com/953690 is the never-to-be-closed bug to track flags that are removed.
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@.