rake_override_task.rb

# This method provides a way for overriding an existing rake task.  Currently,
# in Rake, there is no way to override--only append.
#
# Example usage:
#
#   namespace :db do
#     override_task :migrate => :environment do
#       puts "Do some stuff before!"
#
#       # Call the original task
#       Rake::Task["db:migrate:original"].invoke
#
#       puts "Do some stuff after!"
#     end
#   end

def override_task(*args, &block)
  # Use resolve_args (provided by Rake::Application to break down arguments
  # usually provided to #task.
  name, params, deps = Rake.application.resolve_args(args.dup)

  # Look up the task that we're about to override.
  task = Rake::Task[name]
  # Make sure that the task we're overriding is defined.
  raise "Task #{name} must be defined to override" unless task

  # Create a new task that is an alias of the current one, appending ":original"
  # onto the task name.  Copy over the arg_names, prerequisites and actions
  # of the original task.
  aliased_task = task.application.intern(task.class, "#{task.name}:original")
  aliased_task.set_arg_names(task.arg_names)
  aliased_task.prerequisites.each do |prerequisite|
    aliased_task.enhance(prerequisites)
  end
  aliased_task.actions.each do |action|
    aliased_task.enhance(&action)
  end

  # Clear out the task.
  task.clear

  # Set our new arg_names and enhance the task with our prerequisite and action.
  task.set_arg_names(params)
  task.enhance(deps, &block)
end