Add system note on description change of issue/merge request

app/helpers/system_note_helper.rb

 module SystemNoteHelper
   ICON_NAMES_BY_ACTION = {
     'commit' => 'icon_commit',
+    'description' => 'icon_edit',
     'merge' => 'icon_merge',
     'merged' => 'icon_merged',
     'opened' => 'icon_status_open',

app/models/system_note_metadata.rb

 class SystemNoteMetadata < ActiveRecord::Base
   ICON_TYPES = %w[
-    commit merge confidential visible label assignee cross_reference
+    commit description merge confidential visible label assignee cross_reference
     title time_tracking branch milestone discussion task moved opened closed merged
   ].freeze
 

app/services/issuable_base_service.rb

@@ -24,6 +24,10 @@ class IssuableBaseService < BaseService
       issuable, issuable.project, current_user, old_title)
   end
 
+  def create_description_change_note(issuable)
+    SystemNoteService.change_description(issuable, issuable.project, current_user)
+  end
+
   def create_branch_change_note(issuable, branch_type, old_branch, new_branch)
     SystemNoteService.change_branch(
       issuable, issuable.project, current_user, branch_type,
@@ -289,6 +293,10 @@ class IssuableBaseService < BaseService
       create_title_change_note(issuable, issuable.previous_changes['title'].first)
     end
 
+    if issuable.previous_changes.include?('description')
+      create_description_change_note(issuable)
+    end
+
     if issuable.previous_changes.include?('description') && issuable.tasks?
       create_task_status_note(issuable)
     end

app/services/system_note_service.rb

@@ -261,6 +261,23 @@ module SystemNoteService
     create_note(NoteSummary.new(noteable, project, author, body, action: 'title'))
   end
 
+  # Called when the description of a Noteable is changed
+  #
+  # noteable  - Noteable object that responds to `description`
+  # project   - Project owning noteable
+  # author    - User performing the change
+  #
+  # Example Note text:
+  #
+  #   "changed the description"
+  #
+  # Returns the created Note object
+  def change_description(noteable, project, author)
+    body = "changed the description"
+
+    create_note(NoteSummary.new(noteable, project, author, body, action: 'description'))
+  end
+
   # Called when the confidentiality changes
   #
   # issue   - Issue object

app/views/projects/issues/show.html.haml

@@ -61,7 +61,7 @@
           = markdown_field(@issue, :description)
         %textarea.hidden.js-task-list-field
           = @issue.description
-    = edited_time_ago_with_tooltip(@issue, placement: 'bottom', html_class: 'issue_edited_ago')
+    = edited_time_ago_with_tooltip(@issue, placement: 'bottom', html_class: 'issue_edited_ago', include_author: true)
 
     #merge-requests{ data: { url: referenced_merge_requests_namespace_project_issue_url(@project.namespace, @project, @issue) } }
       // This element is filled in using JavaScript.

app/views/projects/merge_requests/show/_mr_box.html.haml

@@ -10,4 +10,4 @@
         %textarea.hidden.js-task-list-field
           = @merge_request.description
 
-  = edited_time_ago_with_tooltip(@merge_request, placement: 'bottom')
+  = edited_time_ago_with_tooltip(@merge_request, placement: 'bottom', include_author: true)

changelogs/unreleased/add_system_note_for_editing_issuable.yml

+---
+title: Add system note on description change of issue/merge request
+merge_request: 10392
+author: blackst0ne

spec/services/system_note_service_spec.rb

@@ -292,6 +292,20 @@ describe SystemNoteService, services: true do
     end
   end
 
+  describe '.change_description' do
+    subject { described_class.change_description(noteable, project, author) }
+
+    context 'when noteable responds to `description`' do
+      it_behaves_like 'a system note' do
+        let(:action) { 'description' }
+      end
+
+      it 'sets the note text' do
+        expect(subject.note).to eq 'changed the description'
+      end
+    end
+  end
+
   describe '.change_issue_confidentiality' do
     subject { described_class.change_issue_confidentiality(noteable, project, author) }