Show time to require each dependency in your application's Gemfile

rails_bundler_require_benchmark.rb

require "benchmark"
require "rubygems"

ENV["BUNDLE_GEMFILE"] ||= File.expand_path("../../Gemfile", __dir__)
require "bundler/setup"

# https://github.com/rubygems/rubygems/blob/a753447de8fb92dad30e927656984aa2b7765f3d/bundler/lib/bundler/runtime.rb#L46
REQUIRE_ERRORS = [
  /^no such file to load -- (.+)$/i,
  /^Missing \w+ (?:file\s*)?([^\s]+.rb)$/i,
  /^Missing API definition file in (.+)$/i,
  /^cannot load such file -- (.+)$/i,
  /^dlopen\([^)]*\): Library not loaded: (.+)$/i,
].freeze

def load_bundler_dependency(dep)
  return unless dep.should_include?

  required_file = nil

  begin
    # Loop through all the specified autorequires for the
    # dependency. If there are none, use the dependency's name
    # as the autorequire.
    Array(dep.autorequire || dep.name).each do |file|
      # Allow `require: true` as an alias for `require: <name>`
      file = dep.name if file == true
      required_file = file
      begin
        Kernel.require file
      rescue RuntimeError => e
        raise e if e.is_a?(LoadError) # we handle this a little later
        raise Bundler::GemRequireError.new e,
          "There was an error while trying to load the gem '#{file}'."
      end
    end
  rescue LoadError => e
    REQUIRE_ERRORS.find {|r| r =~ e.message }
    raise if dep.autorequire || $1 != required_file

    if dep.autorequire.nil? && dep.name.include?("-")
      begin
        namespaced_file = dep.name.tr("-", "/")
        Kernel.require namespaced_file
      rescue LoadError => e
        REQUIRE_ERRORS.find {|r| r =~ e.message }
        raise if $1 != namespaced_file
      end
    end
  end
end

results = []
results << ["rails/all", Benchmark.measure { require "rails/all" }]

Bundler.setup(*Rails.groups).dependencies.map do |dep|
  results << [dep.name, Benchmark.measure { load_bundler_dependency(dep) }]
end

results.sort_by { |dep, result| result.total }.each do |dep, result|
  puts "%.5fs %s" % [result.total, dep]
end

puts "--------"
puts "%.5fs total" % results.sum { |_, result| result.total }