Remove view_diffs_file_by_file feature flag

This extended commit message satisfies Dangerbot.

app/controllers/projects/merge_requests_controller.rb

@@ -102,7 +102,7 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
         @issuable_sidebar = serializer.represent(@merge_request, serializer: 'sidebar')
         @current_user_data = UserSerializer.new(project: @project).represent(current_user, {}, MergeRequestCurrentUserEntity).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, default_enabled: true) && current_user&.view_diffs_file_by_file
+        @file_by_file_default = 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

@@ -79,13 +79,12 @@
         = 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, 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
-            = s_("Preferences|Show one file at a time on merge request's Changes tab")
-          .form-text.text-muted
-            = s_("Preferences|Instead of all the files changed, show only one file at a time. To switch between files, use the file browser.")
+      .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
+          = s_("Preferences|Show one file at a time on merge request's Changes tab")
+        .form-text.text-muted
+          = s_("Preferences|Instead of all the files changed, show only one file at a time. To switch between files, use the file browser.")
       .form-group
         = f.label :tab_width, s_('Preferences|Tab width'), class: 'label-bold'
         = f.number_field :tab_width,

changelogs/unreleased/229848-feature-flag-enable-option-to-display-one-file-at-a-time-in-mrs.yml

+---
+title: Remove `view_diffs_file_by_file` feature flag
+merge_request: 48966
+author:
+type: other

config/feature_flags/development/view_diffs_file_by_file.yml

----
-name: view_diffs_file_by_file
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/35223
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/229848
-milestone: '13.2'
-type: development
-group: group::code review
-default_enabled: true

doc/user/project/merge_requests/reviewing_and_managing_merge_requests.md

@@ -78,10 +78,7 @@ Click **Expand file** on any file to view the changes for that file.
 ### 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, enabled by default.
-> - It's recommended for production use.
-> - It's enabled on GitLab.com.
-> - For GitLab self-managed instances, GitLab administrators can opt to [disable it](#enable-or-disable-file-by-file-diff-navigation).
+> - [Feature flag removed](https://gitlab.com/gitlab-org/gitlab/-/issues/229848) in GitLab 13.7.
 
 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 navigation bar, click **Settings**, and go to **Preferences** on the left
@@ -103,27 +100,6 @@ merge request:
 This change overrides the choice you made in your user preferences and persists until you clear your
 browser's cookies or change this behavior again.
 
-#### 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 **enabled by default**.
-[GitLab administrators with access to the GitLab Rails console](../../../administration/feature_flags.md)
-can opt to disable it for your instance.
-
-To enable it:
-
-```ruby
-# Instance-wide
-Feature.enable(:view_diffs_file_by_file)
-```
-
-To disable it:
-
-```ruby
-# Instance-wide
-Feature.disable(:view_diffs_file_by_file>)
-```
-
 ### Merge requests commit navigation
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/18140) in GitLab 13.0.