Move participants method to shared Participable concern.

app/models/commit.rb

@@ -3,8 +3,10 @@ class Commit
   include StaticModel
   extend ActiveModel::Naming
   include Mentionable
+  include Participable
 
   attr_mentionable :safe_message
+  participant :author, :committer, :notes, :mentioned_users
 
   attr_accessor :project
 
@@ -137,21 +139,6 @@ class Commit
     User.find_for_commit(committer_email, committer_name)
   end
 
-  def participants(current_user = nil)
-    users = []
-    users << author
-    users << committer
-    
-    users.push *self.mentioned_users(current_user)
-
-    notes.each do |note|
-      users << note.author
-      users.push *note.mentioned_users(current_user)
-    end
-
-    users.uniq
-  end
-
   def notes
     project.notes.for_commit_id(self.id)
   end

app/models/concerns/issuable.rb

@@ -7,6 +7,7 @@
 module Issuable
   extend ActiveSupport::Concern
   include Mentionable
+  include Participable
 
   included do
     belongs_to :author, class_name: "User"
@@ -45,6 +46,7 @@ module Issuable
              prefix: true
 
     attr_mentionable :title, :description
+    participant :author, :assignee, :notes, :mentioned_users
   end
 
   module ClassMethods
@@ -117,22 +119,6 @@ module Issuable
     upvotes + downvotes
   end
 
-  # Return all users participating on the discussion
-  def participants(current_user = self.author)
-    users = []
-    users << author
-    users << assignee if is_assigned?
-
-    users.push *self.mentioned_users(current_user)
-
-    notes.each do |note|
-      users << note.author
-      users.push *note.mentioned_users(current_user)
-    end
-
-    users.uniq
-  end
-
   def subscribed?(user)
     subscription = subscriptions.find_by_user_id(user.id)
 

app/models/concerns/participable.rb

@@ -0,0 +1,42 @@
+module Participable
+  extend ActiveSupport::Concern
+
+  module ClassMethods
+    def participant(*attrs)
+      participant_attrs.concat(attrs.map(&:to_s))
+    end
+
+    def participant_attrs
+      @participant_attrs ||= []
+    end
+  end
+
+  def participants(current_user = self.author)
+    self.class.participant_attrs.flat_map do |attr|
+      meth = method(attr)
+
+      value = 
+        if meth.arity == 1
+          meth.call(current_user)
+        else
+          meth.call
+        end
+
+      participants_for(value, current_user)
+    end.compact.uniq
+  end
+
+  private
+    def participants_for(value, current_user = nil)
+      case value
+      when User
+        [value]
+      when Array
+        value.flat_map { |v| participants_for(v, current_user) }
+      when Participable
+        value.participants(current_user)
+      when Mentionable
+        value.mentioned_users(current_user)
+      end
+    end
+end

app/models/note.rb

@@ -23,10 +23,12 @@ require 'file_size_validator'
 class Note < ActiveRecord::Base
   include Mentionable
   include Gitlab::CurrentSettings
+  include Participable
 
   default_value_for :system, false
 
   attr_mentionable :note
+  participant :author, :mentioned_users
 
   belongs_to :project
   belongs_to :noteable, polymorphic: true

app/models/snippet.rb

@@ -19,6 +19,7 @@ class Snippet < ActiveRecord::Base
   include Sortable
   include Linguist::BlobHelper
   include Gitlab::VisibilityLevel
+  include Participable
 
   default_value_for :visibility_level, Snippet::PRIVATE
 
@@ -47,6 +48,8 @@ class Snippet < ActiveRecord::Base
   scope :expired, -> { where(["expires_at IS NOT NULL AND expires_at < ?", Time.current]) }
   scope :non_expired, -> { where(["expires_at IS NULL OR expires_at > ?", Time.current]) }
 
+  participant :author, :notes
+
   def self.content_types
     [
       ".rb", ".py", ".pl", ".scala", ".c", ".cpp", ".java",
@@ -87,18 +90,6 @@ class Snippet < ActiveRecord::Base
     visibility_level
   end
 
-  def participants(current_user = self.author)
-    users = []
-    users << author
-    
-    notes.each do |note|
-      users << note.author
-      users.push *note.mentioned_users(current_user)
-    end
-
-    users.uniq
-  end
-
   class << self
     def search(query)
       where('(title LIKE :query OR file_name LIKE :query)', query: "%#{query}%")