## Summary Roll out [Rapid Diffs as the default on the merge request Changes tab](https://gitlab.com/gitlab-org/gitlab/-/issues/602723) currently behind the `rapid_diffs_default_on_mr_show` feature flag. - DRI: @slashmanov - Team Slack channel: `#g_code-review` > [!note] > Process and guidance live in the docs — this issue is just the commands and a place to track the rollout. > "Rolling out" means incrementally enabling the flag on GitLab.com to validate stability — it is not the same as releasing the feature, which happens when the flag is removed. > [Feature flag controls](https://docs.gitlab.com/development/feature_flags/controls/) · [Feature flag lifecycle](https://handbook.gitlab.com/handbook/product-development/how-we-work/product-development-flow/feature-flag-lifecycle/#feature-flag-lifecycle) Introduced by https://gitlab.com/gitlab-org/gitlab/-/merge_requests/247629. With the flag enabled, the Changes tab renders Rapid Diffs without opt-in; the in-MR toggle becomes an opt-*out* that sets `rapid_diffs_enabled=false`. With the flag disabled, today's opt-in behaviour is unchanged. This flag sits behind the existing `rapid_diffs_on_mr_show` beta flag, so it only takes effect where Rapid Diffs is already available. ## What could go wrong? Blast radius is every merge request Changes tab view on GitLab.com, so this is best rolled out by actor percentage and watched closely. - Rapid Diffs regressions that were previously only seen by opted-in users now hit everyone. Users can escape via the toggle (opt-out cookie) or the `?rapid_diffs_disabled=true` URL parameter. - The route constraint evaluates the flag without an actor, while the controller re-checks it with `current_user`. During a percentage-of-actors rollout the two can disagree; the controller redirects with `rapid_diffs_disabled=true` so this degrades to legacy diffs rather than a redirect loop. Watch for a spike in redirects to `/diffs?rapid_diffs_disabled=true`. - Watch the `Projects::MergeRequestsController` error rate and latency on [dashboards.gitlab.net](https://dashboards.gitlab.net), plus Sentry for `rapid_diffs` frontend errors. ## Rollout Run all production `/chatops` in [`#production`](https://gitlab.slack.com/archives/C101F3796) and cross-post the results to `#g_code-review`. Background: [incremental rollout process](https://docs.gitlab.com/development/feature_flags/controls/#process), [feature actors](https://docs.gitlab.com/development/feature_flags/#feature-actors). **Non-production** ``` /chatops gitlab run feature set rapid_diffs_default_on_mr_show 50 --actors --dev --pre --staging --staging-ref /chatops gitlab run feature set rapid_diffs_default_on_mr_show true --dev --pre --staging --staging-ref ``` **Production** — dogfood on the GitLab organisation first: ``` /chatops gitlab run feature set --group=gitlab-org,gitlab-com rapid_diffs_default_on_mr_show true ``` Then percentage rollout (wait ≥15 min between steps, watch dashboards): ``` /chatops gitlab run feature set rapid_diffs_default_on_mr_show 10 --actors /chatops gitlab run feature set rapid_diffs_default_on_mr_show 25 --actors /chatops gitlab run feature set rapid_diffs_default_on_mr_show 50 --actors /chatops gitlab run feature set rapid_diffs_default_on_mr_show 100 --actors ``` - [ ] Enabled on `--dev --pre --staging --staging-ref` - [ ] Enabled for `gitlab-org` / `gitlab-com` - [ ] 10% of actors - [ ] 25% of actors - [ ] 50% of actors - [ ] 100% of actors ## Before global rollout Confirm the relevant gotchas before going to 100% — see [enabling a feature for GitLab.com](https://docs.gitlab.com/development/feature_flags/controls/#enabling-a-feature-for-gitlabcom): - [ ] [Docs + version history](https://docs.gitlab.com/development/documentation/feature_flags/) updated - [ ] [Breaking changes](https://docs.gitlab.com/development/documentation/release_notes/#deprecations-removals-and-breaking-changes) announced, if any - [ ] [Change management issue](https://handbook.gitlab.com/handbook/engineering/infrastructure-platforms/change-management/#feature-flags-and-the-change-management-process) opened, if required - [ ] Merge request spec suite migrated to Rapid Diffs so the suite no longer relies on the global `stub_feature_flags(rapid_diffs_default_on_mr_show: false)` guard ## Cleanup Remove the flag once [deemed stable](https://handbook.gitlab.com/handbook/product-development/how-we-work/product-development-flow/feature-flag-lifecycle/#feature-flag-lifecycle) — see [cleaning up](https://docs.gitlab.com/development/feature_flags/controls/#cleaning-up). Removing this flag means making Rapid Diffs the unconditional default in the route constraint and `Projects::MergeRequestsController#rapid_diffs_page_enabled?`, and dropping the global spec stub. ``` /chatops gitlab run release check <merge-request-url> <milestone> /chatops gitlab run feature delete rapid_diffs_default_on_mr_show --dev --pre --staging --staging-ref --production ```