Enables diff file-by-file navigation by default

app/controllers/projects/merge_requests_controller.rb

@@ -84,7 +84,7 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
         @issuable_sidebar = serializer.represent(@merge_request, serializer: 'sidebar')
         @current_user_data = UserSerializer.new(project: @project).represent(current_user, {}, MergeRequestUserEntity).to_json
         @show_whitespace_default = current_user.nil? || current_user.show_whitespace_in_diffs
-        @file_by_file_default = Feature.enabled?(:view_diffs_file_by_file) && current_user&.view_diffs_file_by_file
+        @file_by_file_default = Feature.enabled?(:view_diffs_file_by_file, default_enabled: true) && current_user&.view_diffs_file_by_file
         @coverage_path = coverage_reports_project_merge_request_path(@project, @merge_request, format: :json) if @merge_request.has_coverage_reports?
         @endpoint_metadata_url = endpoint_metadata_url(@project, @merge_request)
 

app/views/profiles/preferences/show.html.haml

@@ -70,7 +70,7 @@
       = f.check_box :show_whitespace_in_diffs, class: 'form-check-input'
       = f.label :show_whitespace_in_diffs, class: 'form-check-label' do
         = s_('Preferences|Show whitespace changes in diffs')
-    - if Feature.enabled?(:view_diffs_file_by_file)
+    - if Feature.enabled?(:view_diffs_file_by_file, default_enabled: true)
       .form-group.form-check
         = f.check_box :view_diffs_file_by_file, class: 'form-check-input'
         = f.label :view_diffs_file_by_file, class: 'form-check-label' do

doc/user/project/merge_requests/reviewing_and_managing_merge_requests.md

@@ -67,9 +67,10 @@ list.
 ### File-by-file diff navigation
 
 > - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/222790) in GitLab 13.2.
-> - It's deployed behind a feature flag, disabled by default.
+> - It's deployed behind a feature flag, enabled by default.
+> - It's recommended for production use.
 > - It's enabled on GitLab.com.
-> - To use it in GitLab self-managed instances, ask a GitLab administrator to [enable it](#enable-or-disable-file-by-file-diff-navigation-core-only).
+> - For GitLab self-managed instances, GitLab administrators can opt to [disable it](#enable-or-disable-file-by-file-diff-navigation-core-only).
 
 For larger merge requests it might sometimes be useful to review single files at a time. To enable,
 from your avatar on the top-right navbar, click **Settings**, and go to **Preferences** on the left
@@ -83,9 +84,9 @@ From there, when reviewing merge requests' **Changes** tab, you will see only on
 #### Enable or disable file-by-file diff navigation **(CORE ONLY)**
 
 File-by-file diff navigation is under development but ready for production use. It is
-deployed behind a feature flag that is **disabled by default**.
+deployed behind a feature flag that is **enabled by default**.
 [GitLab administrators with access to the GitLab Rails console](../../../administration/feature_flags.md)
-can enable it for your instance.
+can opt to disable it for your instance.
 
 To enable it: