FEATURE: Allow plugins to register a callback to ignore DraftSequence.

app/models/draft_sequence.rb

@@ -5,7 +5,7 @@ class DraftSequence < ActiveRecord::Base
     user_id = user
     user_id = user.id unless user.is_a?(Integer)
 
-    return 0 if user_id < 0
+    return 0 if invalid_user_id?(user_id)
 
     h = { user_id: user_id, draft_key: key }
     c = DraftSequence.find_by(h)
@@ -23,12 +23,22 @@ class DraftSequence < ActiveRecord::Base
     user_id = user
     user_id = user.id unless user.is_a?(Integer)
 
-    return nil if user_id < 0
+    return nil if invalid_user_id?(user_id)
 
     # perf critical path
     r, _ = DB.query_single('select sequence from draft_sequences where user_id = ? and draft_key = ?', user_id, key)
     r.to_i
   end
+
+  cattr_accessor :plugin_ignore_draft_sequence_callbacks
+  self.plugin_ignore_draft_sequence_callbacks = {}
+
+  def self.invalid_user_id?(user_id)
+    user_id < 0 || self.plugin_ignore_draft_sequence_callbacks.any? do |plugin, callback|
+      plugin.enabled? ? callback.call(user_id) : false
+    end
+  end
+  private_class_method :invalid_user_id?
 end
 
 # == Schema Information

lib/plugin/instance.rb

@@ -409,6 +409,15 @@ class Plugin::Instance
     SeedFu.fixture_paths.concat(paths)
   end
 
+  # Applies to all sites in a multisite environment. Block is not called if
+  # plugin is not enabled. Block is called with `user_id` and has to return a
+  # boolean based on whether the given `user_id` should be ignored.
+  def register_ignore_draft_sequence_callback(&block)
+    reloadable_patch do |plugin|
+      ::DraftSequence.plugin_ignore_draft_sequence_callbacks[plugin] = block
+    end
+  end
+
   def listen_for(event_name)
     return unless self.respond_to?(event_name)
     DiscourseEvent.on(event_name, &self.method(event_name))