[Feature flag] Rollout of introduce_marker_ranges

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• Label this issue

What

Remove the :introduce_marker_ranges feature flag ...

Owners

• Team: groupsource code
• Most appropriate slack channel to reach out to: #g_create_source-code-be
• Best individual to reach out to: @vyaklushin

Expectations

What are we expecting to happen?

InlineDiffMarker will process Gitlab::MarkerRange instead of Range objects.

A new class ("addition" or "deletion") will be added to lines on a merge request diff page. It should have no negative effect because these classes are overwritten by other CSS rules.

What might happen if this goes wrong?

The highlighting might look strange.

What can we monitor to detect problems with this?

Beta groups/projects

If applicable, any groups/projects that are happy to have this feature turned on early. Some organizations may wish to test big changes they are interested in with a small subset of users ahead of time for example.

• gitlab-org/gitlab project
• gitlab-org/gitlab-com groups
• ...

Roll Out Steps

• Enable on staging (/chatops run feature set introduce_marker_ranges true --staging)
• Test on staging
• Ensure that documentation has been updated
• Enable on GitLab.com for individual groups/projects listed above and verify behaviour (/chatops run feature set --project=gitlab-org/gitlab introduce_marker_ranges true)
• Coordinate a time to enable the flag with the SRE oncall and release managers
  • In #production mention @sre-oncall and @release-managers. Once an SRE on call and Release Manager on call confirm, you can proceed with the rollout
• Announce on the issue an estimated time this will be enabled on GitLab.com
• Enable on GitLab.com by running chatops command in #production (/chatops run feature set introduce_marker_ranges true)
• Cross post chatops Slack command to #support_gitlab-com (more guidance when this is necessary in the dev docs) and in your team channel
• Announce on the issue that the flag has been enabled
• Remove feature flag and add changelog entry. Ensure that the feature flag definition YAML file has been removed in the same MR that is removing the feature flag from the code
• After the flag removal is deployed, clean up the feature flag by running chatops command in #production channel

Rollback Steps

• This feature can be disabled by running the following Chatops command:

/chatops run feature set --project=gitlab-org/gitlab introduce_marker_ranges false