At mention participating users.

app/controllers/projects_controller.rb

@@ -123,11 +123,12 @@ class ProjectsController < ApplicationController
   end
 
   def autocomplete_sources
+    participating_users = @project.team.members.sort_by(&:username).map { |user| { username: user.username, name: user.name } } + User.participating(@project.notes).select([:username, :name]).sort_by(&:username).map { |user| { username: user.username, name: user.name } }
     @suggestions = {
       emojis: Emoji.names.map { |e| { name: e, path: view_context.image_url("emoji/#{e}.png") } },
       issues: @project.issues.select([:iid, :title, :description]),
       mergerequests: @project.merge_requests.select([:iid, :title, :description]),
-      members: @project.team.members.sort_by(&:username).map { |user| { username: user.username, name: user.name } }
+      members: participating_users.uniq
     }
 
     respond_to do |format|

app/models/user.rb

@@ -169,6 +169,7 @@ class User < ActiveRecord::Base
   scope :not_in_project, ->(project) { project.users.present? ? where("id not in (:ids)", ids: project.users.map(&:id) ) : all }
   scope :without_projects, -> { where('id NOT IN (SELECT DISTINCT(user_id) FROM users_projects)') }
   scope :ldap, -> { where(provider:  'ldap') }
+  scope :participating, ->(notes){ where(id: notes.inc_author.map(&:author_id))}
 
   scope :potential_team_members, ->(team) { team.members.any? ? active.not_in_team(team) : active  }