Add system note with link to diff comparison when MR discussion becomes outdated

4 files changed, 40 insertions, 15 deletions

diff --git a/app/services/merge_requests/refresh_service.rb b/app/services/merge_requests/refresh_service.rb
index 1131d6f4913..81d217929d5 100644
--- a/app/services/merge_requests/refresh_service.rb
+++ b/app/services/merge_requests/refresh_service.rb
@@ -66,12 +66,12 @@ module MergeRequests
 
       filter_merge_requests(merge_requests).each do |merge_request|
         if merge_request.source_branch == @branch_name || force_push?
-          merge_request.reload_diff
+          merge_request.reload_diff(current_user)
         else
           mr_commit_ids = merge_request.commits_sha
           push_commit_ids = @commits.map(&:id)
           matches = mr_commit_ids & push_commit_ids
-          merge_request.reload_diff if matches.any?
+          merge_request.reload_diff(current_user) if matches.any?
         end
 
         merge_request.mark_as_unchecked
diff --git a/app/services/merge_requests/reopen_service.rb b/app/services/merge_requests/reopen_service.rb
index fadcce5d9b6..54b19e6d651 100644
--- a/app/services/merge_requests/reopen_service.rb
+++ b/app/services/merge_requests/reopen_service.rb
@@ -8,7 +8,7 @@ module MergeRequests
         create_note(merge_request)
         notification_service.reopen_mr(merge_request, current_user)
         execute_hooks(merge_request, 'reopen')
-        merge_request.reload_diff
+        merge_request.reload_diff(current_user)
         merge_request.mark_as_unchecked
       end
 
diff --git a/app/services/notes/diff_position_update_service.rb b/app/services/notes/diff_position_update_service.rb
index 0cb731f5bc3..eff7b287269 100644
--- a/app/services/notes/diff_position_update_service.rb
+++ b/app/services/notes/diff_position_update_service.rb
@@ -1,26 +1,29 @@
 module Notes
   class DiffPositionUpdateService < BaseService
     def execute(note)
-      new_position = tracer.trace(note.position)
+      results = tracer.trace(note.position)
+      return unless results
 
-      # Don't update the position if the type doesn't match, since that means
-      # the diff line commented on was changed, and the comment is now outdated
-      old_position = note.position
-      if new_position &&
-          new_position != old_position &&
-          new_position.type == old_position.type
+      position = results[:position]
+      outdated = results[:outdated]
 
-        note.position = new_position
-      end
+      if outdated
+        note.change_position = position
 
-      note
+        if note.persisted? && current_user
+          SystemNoteService.diff_discussion_outdated(note.to_discussion, project, current_user, position)
+        end
+      else
+        note.position = position
+        note.change_position = nil
+      end
     end
 
     private
 
     def tracer
       @tracer ||= Gitlab::Diff::PositionTracer.new(
-        repository: project.repository,
+        project: project,
         old_diff_refs: params[:old_diff_refs],
         new_diff_refs: params[:new_diff_refs],
         paths: params[:paths]
diff --git a/app/services/system_note_service.rb b/app/services/system_note_service.rb
index 93bf1fb1615..0837c07e6aa 100644
--- a/app/services/system_note_service.rb
+++ b/app/services/system_note_service.rb
@@ -258,7 +258,7 @@ module SystemNoteService
     create_note(NoteSummary.new(noteable, project, author, body, action: 'title'))
   end
 
-  def self.resolve_all_discussions(merge_request, project, author)
+  def resolve_all_discussions(merge_request, project, author)
     body = "resolved all discussions"
 
     create_note(NoteSummary.new(merge_request, project, author, body, action: 'discussion'))
@@ -274,6 +274,28 @@ module SystemNoteService
     note
   end
 
+  def diff_discussion_outdated(discussion, project, author, change_position)
+    merge_request = discussion.noteable
+    diff_refs = change_position.diff_refs
+    version_index = merge_request.merge_request_diffs.viewable.count
+
+    body = "changed this line in"
+    if version_params = merge_request.version_params_for(diff_refs)
+      line_code = change_position.line_code(project.repository)
+      url = url_helpers.diffs_namespace_project_merge_request_url(project.namespace, project, merge_request, version_params.merge(anchor: line_code))
+
+      body << " [version #{version_index} of the diff](#{url})"
+    else
+      body << " version #{version_index} of the diff"
+    end
+
+    note_attributes = discussion.reply_attributes.merge(project: project, author: author, note: body)
+    note = Note.create(note_attributes.merge(system: true))
+    note.system_note_metadata = SystemNoteMetadata.new(action: 'outdated')
+
+    note
+  end
+
   # Called when the title of a Noteable is changed
   #
   # noteable  - Noteable object that responds to `title`