How can I disable logging of asset pipeline (sprockets) messages in Ruby on Rails 3.1?

Place the following code in config/initializers/quiet_assets.rb

if Rails.env.development?
  Rails.application.assets.try(:logger=, Logger.new('/dev/null'))
  Rails::Rack::Logger.class_eval do
    def call_with_quiet_assets(env)
      previous_level = Rails.logger.level
      Rails.logger.level = Logger::ERROR if env['PATH_INFO'] =~ %r{^/assets/}
      call_without_quiet_assets(env)
    ensure
      Rails.logger.level = previous_level
    end
    alias_method_chain :call, :quiet_assets
  end
end

Updated: It now works for Ruby on Rails 3.2 too (previous attempt fixes before_dispatch, and now we're going for the root rack call instead)

Update: A proper Rack middleware solution (instead of fragile alias_method_chain) from @macournoyer https://github.com/rails/rails/issues/2639#issuecomment-6591735

Take a look at https://github.com/evrone/quiet_assets and just include it into your Gem file.

For the lazy: gem 'quiet_assets', group: :development

For Ruby on Rails 3.2, add config.assets.logger = false to your development environment configuration file, typically found at config/environments/development.rb. See #4512.