Do some small refacto plus add the changelog entry

app/helpers/push_rules_helper.rb

@@ -5,7 +5,6 @@ module PushRulesHelper
     annotate_with_update_message(message, push_rule,
                                  enabled_globally: PushRule.global&.reject_unsigned_commits,
                                  enabled_in_project: push_rule.reject_unsigned_commits)
-    message.join(' ')
   end
 
   def commit_author_check_description(push_rule)
@@ -14,7 +13,6 @@ module PushRulesHelper
     annotate_with_update_message(message, push_rule,
                                  enabled_globally: PushRule.global&.commit_author_check,
                                  enabled_in_project: push_rule.commit_author_check)
-    message.join(' ')
   end
 
   private
@@ -33,5 +31,7 @@ module PushRulesHelper
         message << s_("ProjectSettings|Contact an admin to change this setting.") unless current_user.admin?
       end
     end
+
+    message.join(' ')
   end
 end

app/models/push_rule.rb

@@ -5,7 +5,10 @@ class PushRule < ActiveRecord::Base
   validates :max_file_size, numericality: { greater_than_or_equal_to: 0, only_integer: true }
 
   FILES_BLACKLIST = YAML.load_file(Rails.root.join('lib/gitlab/checks/files_blacklist.yml'))
-  SETTINGS_WITH_GLOBAL_DEFAULT = %i[reject_unsigned_commits commit_author_check].freeze
+  SETTINGS_WITH_GLOBAL_DEFAULT = %i[
+    reject_unsigned_commits
+    commit_author_check
+  ].freeze
 
   SETTINGS_WITH_GLOBAL_DEFAULT.each do |setting|
     define_method(setting) do

app/views/shared/push_rules/_form.html.haml

 = render 'shared/push_rules/reject_unsigned_commits_setting', form: f, push_rule: f.object
 
 .form-group
-  = f.check_box :commit_author_check, class: "pull-left", disabled: !can_change_commit_author_check?(f.object)
+  = f.check_box :commit_author_check, class: "pull-left", disabled: !can_change_push_rule?(f.object, :commit_author_check)
   .prepend-left-20
     = f.label :commit_author_check, class: "label-light append-bottom-0" do
       Author restriction

changelogs/unreleased/add_commit_author_check_feature.yml

+---
+title: Add new push rule to enforce that only the author of a commit can push to the repository
+merge_request: 3086
+author:
+type: added

ee/app/helpers/ee/projects_helper.rb

 module EE
   module ProjectsHelper
-    def can_change_reject_unsigned_commits?(push_rule)
+    def can_change_push_rule?(push_rule, rule)
       return true if push_rule.global?
 
-      can?(current_user, :change_reject_unsigned_commits, @project)
-    end
-
-    def can_change_commit_author_check?(push_rule)
-      return true if push_rule.global?
-
-      can?(current_user, :change_commit_author_check, @project)
+      can?(current_user, :"change_#{rule}", @project)
     end
   end
 end