Add 'Resolved all discussions' system note

app/controllers/projects/discussions_controller.rb

@@ -9,6 +9,8 @@ class Projects::DiscussionsController < Projects::ApplicationController
     discussion.resolve!(current_user)
+    MergeRequests::AllDiscussionsResolvedService.new(project, current_user).execute(merge_request)
+
     render json: {
       resolved_by: discussion.resolved_by.try(:name),
       discussion_headline_html: view_to_html_string('discussions/_headline', discussion: discussion)

app/controllers/projects/notes_controller.rb

@@ -72,6 +72,8 @@ class Projects::NotesController < Projects::ApplicationController
     note.resolve!(current_user)
+    MergeRequests::AllDiscussionsResolvedService.new(project, current_user).execute(note.noteable)
+
     discussion = note.discussion
     render json: {

app/models/merge_request.rb

@@ -401,6 +401,11 @@ class MergeRequest < ActiveRecord::Base
       discussions
   end
+  def discussions_resolved?
+    all_discussions = discussions
+    all_discussions.any?(&:resolvable?) && all_discussions.none?(&:to_be_resolved?)
+  end
+
   def hook_attrs
     attrs = {
       source: source_project.try(:hook_attrs),

app/services/merge_requests/all_discussions_resolved_service.rb

+module MergeRequests
+  class AllDiscussionsResolvedService < MergeRequests::BaseService
+    def execute(merge_request)
+      return unless merge_request.discussions_resolved?
+
+      SystemNoteService.resolve_all_discussions(merge_request, project, current_user)
+    end
+  end
+end

app/services/notes/delete_service.rb

@@ -3,6 +3,10 @@ module Notes
     def execute(note)
       note.destroy
       note.reset_events_cache
+
+      if note.resolvable?
+        MergeRequests::AllDiscussionsResolvedService.new(project, current_user).execute(note.noteable)
+      end
     end
   end
 end

app/services/system_note_service.rb

@@ -156,6 +156,12 @@ class SystemNoteService
     create_note(noteable: noteable, project: project, author: author, note: body)
   end
+  def self.resolve_all_discussions(merge_request, project, author)
+    body = "Resolved all discussions"
+
+    create_note(noteable: merge_request, project: project, author: author, note: body)
+  end
+
   # Called when the title of a Noteable is changed
   #
   # noteable  - Noteable object that responds to `title`