Add 'show_whitespace_in_diffs' to the UserPreferences endpoint

This will allow frontend build out syncing of the preference.

Changelog: added

doc/api/users.md

@@ -451,6 +451,7 @@ Parameters:
 | `twitter`                            | No       | Twitter account                                                                                                                                         |
 | `username`                           | Yes      | Username                                                                                                                                                |
 | `view_diffs_file_by_file`            | No       | Flag indicating the user sees only one file diff per page                                                                                               |
+| `show_whitespace_in_diffs`           | No       | Flag indicating the user sees whitespace changes in diffs
 | `website_url`                        | No       | Website URL                                                                                                                                             |
 
 ## User modification

lib/api/entities/user_preferences.rb

@@ -3,7 +3,7 @@
 module API
   module Entities
     class UserPreferences < Grape::Entity
-      expose :id, :user_id, :view_diffs_file_by_file
+      expose :id, :user_id, :view_diffs_file_by_file, :show_whitespace_in_diffs
     end
   end
 end

lib/api/users.rb

@@ -1025,7 +1025,9 @@ module API
         detail 'This feature was introduced in GitLab 13.10.'
       end
       params do
-        requires :view_diffs_file_by_file, type: Boolean, desc: 'Flag indicating the user sees only one file diff per page'
+        optional :view_diffs_file_by_file, type: Boolean, desc: 'Flag indicating the user sees only one file diff per page'
+        optional :show_whitespace_in_diffs, type: Boolean, desc: 'Flag indicating the user sees whitespace changes in diffs'
+        at_least_one_of :view_diffs_file_by_file, :show_whitespace_in_diffs
       end
       put "preferences", feature_category: :users do
         authenticate!

spec/requests/api/users_preferences_spec.rb

@@ -8,11 +8,19 @@ RSpec.describe API::Users do
   describe 'PUT /user/preferences/' do
     context "with correct attributes and a logged in user" do
       it 'returns a success status and the value has been changed' do
-        put api("/user/preferences", user), params: { view_diffs_file_by_file: true }
+        put api("/user/preferences", user), params: {
+          view_diffs_file_by_file: true,
+          show_whitespace_in_diffs: true
+        }
 
         expect(response).to have_gitlab_http_status(:ok)
         expect(json_response['view_diffs_file_by_file']).to eq(true)
-        expect(user.reload.view_diffs_file_by_file).to be_truthy
+        expect(json_response['show_whitespace_in_diffs']).to eq(true)
+
+        user.reload
+
+        expect(user.view_diffs_file_by_file).to be_truthy
+        expect(user.show_whitespace_in_diffs).to be_truthy
       end
     end