Properly fire update_email hook after commit which changes user email

app/models/concerns/track_saved_changes.rb

@@ -0,0 +1,50 @@
+# https://github.com/ccmcbeck/after-commit
+module TrackSavedChanges
+  extend ActiveSupport::Concern
+
+  included do
+    # expose the details if consumer wants to do more
+    attr_reader :saved_changes_history, :saved_changes_unfiltered
+    after_initialize :reset_saved_changes
+    after_save :track_saved_changes
+  end
+
+  # on initalize, but useful for fine grain control
+  def reset_saved_changes
+    @saved_changes_unfiltered = {}
+    @saved_changes_history = []
+  end
+
+  # filter out any changes that result in the original value
+  def saved_changes
+    @saved_changes_unfiltered.reject { |k,v| v[0] == v[1] }
+  end
+
+  private
+
+  # on save
+  def track_saved_changes
+    # maintain an array of ActiveModel::Dirty.changes
+    @saved_changes_history << changes.dup
+    # accumulate the most recent changes
+    @saved_changes_history.last.each_pair { |k, v| track_saved_change k, v }
+  end
+
+  # v is an an array of [prev, current]
+  def track_saved_change(k, v)
+    if @saved_changes_unfiltered.key? k
+      @saved_changes_unfiltered[k][1] = track_saved_value v[1]
+    else
+      @saved_changes_unfiltered[k] = v.dup
+    end
+  end
+
+  # type safe dup inspred by http://stackoverflow.com/a/20955038
+  def track_saved_value(v)
+    begin
+      v.dup
+    rescue TypeError
+      v
+    end
+  end
+end

app/models/user.rb

@@ -82,7 +82,12 @@ class User < ApplicationRecord
 
   after_create_commit :mailbluster_create_lead
   after_destroy_commit :mailbluster_delete_lead
-  after_update_commit :mailbluster_update_email, if: :saved_change_to_email?
+  # Note that because a commit may cause multiple changes
+  # which are not fully tracked by ActiveRecord::Dirty,
+  # we must resort to using a ActiveRecord::Concern which accumulates
+  # changes from a commit (app/models/concerns/track_saved_changes.rb)
+  # See https://github.com/ccmcbeck/after-commit
+  after_update_commit :mailbluster_update_email, if: ->(obj){ obj.saved_changes.key? 'email' }
 
   # add scope
   scope :comment_notifiable, ->(conference) {joins(:roles).where('roles.name IN (?)', [:organizer, :cfp]).where('roles.resource_type = ? AND roles.resource_id = ?', 'Conference', conference.id)}
@@ -386,7 +391,7 @@ class User < ApplicationRecord
 
   def mailbluster_update_email
     # FIXME: May fail if multiple saves occur in one commit
-    MailblusterEditLeadJob.perform_later(self, old_email: email_before_last_save)
+    MailblusterEditLeadJob.perform_later(self, old_email: self.saved_changes['email'][0])
   end
 
   def touch_events