Load cops lazily instead of requiring all 271 files at startup

[tas50]

What

lib/cookstyle.rb globbed lib/rubocop/cop/**/*.rb and required every file, so every invocation parsed and defined all 270 cop classes before inspecting a single line — including cookstyle --version and runs narrowed to one cop with --only.

This applies the technique RuboCop core added in 1.89 and rubocop-performance adopted in rubocop/rubocop-performance#530. RuboCop::Cop::LazyLoader#register_cop does two things: it sets an autoload for the cop's constant, and it registers the cop's name with RuboCop's global registry as a string. The registry can then validate the config, resolve --only arguments, and list departments knowing only names. A cop's file is read the first time the class itself is needed — which, for a cop disabled in the config, is never.

Registrations live in two new files, lib/rubocop/cop/chef.rb and lib/rubocop/cop/inspec.rb, in the same order the files were previously required, so cop execution order is unchanged.

module RuboCop
  module Cop
    module Chef
      module Correctness
        extend LazyLoader

        register_cop :BlockGuardWithOnlyString, "#{__dir__}/chef/correctness/block_guard_clause_string_only"
        register_cop :ChefApplicationFatal, "#{__dir__}/chef/correctness/chef_application_fatal"
        ...

No cop files were moved or renamed. register_cop takes an explicit path, so the 92 cops whose class name doesn't match their filename and the directories that don't match their department (chef/deprecation/ → Chef::Deprecations, chef/redundant/ → Chef::RedundantCode, chefstyle/ruby/ → Chef::Ruby) all work as they are.

Benchmark

Ruby 4.0.6, macOS arm64, RuboCop 1.90.0. Median of 15 runs, before and after measured back to back on the same machine. Fixture is a 4-file cookbook.

Scenario	Before	After	Change
require "cookstyle" (isolated, excludes Ruby/Bundler boot)	488.4 ms	394.9 ms	−93.5 ms / −19.1%
cookstyle --version (end to end)	755.8 ms	632.9 ms	−122.9 ms / −16.3%
cookstyle --only Chef/Modernize/FoodcriticComments (1 file)	760.2 ms	687.7 ms	−72.5 ms / −9.5%
cookstyle full lint (4-file cookbook)	1014.3 ms	992.7 ms	−21.6 ms / −2.1%

Cop files read during require "cookstyle":

	Before	After
Cop classes loaded at require time	271	0

And loaded over the life of a real run:

Run	Cops loaded
cookstyle --version	0 of 270
cookstyle --only <one cop>	1 of 270
cookstyle full cookbook lint	249 of 270

The full-lint case still improves because the 21 cops disabled in cookstyle.yml are now never loaded at all. The --version and --only cases are where the win is largest, and those matter for editor integrations and for the tools that embed Cookstyle.

Reproduce the isolated require measurement with:

for i in $(seq 1 15); do
  bundle exec ruby -e 't0 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
    require "cookstyle"
    puts(((Process.clock_gettime(Process::CLOCK_MONOTONIC) - t0) * 1000).round(1))'
done | sort -n

Correctness

• --format json output is byte-for-byte identical before and after, both on a cookbook fixture and across this repository's 557 Ruby files (11 offenses, same cops, same lines, same messages).
• Full suite green: 1245 examples, 0 failures.
• rake validate_config, bundle exec cookstyle, --chefstyle, --show-cops, --only <cop>, --only <department>, and -a all verified by hand.
• rake generate_cops_yml_documentation and rake update_readme_cop_count still work — the docs task goes through Registry#cops/#sort!, which force every lazy cop to load.

Keeping registrations honest

Lazy loading means adding a cop file is no longer enough to ship a cop, so spec/lazy_cop_loading_spec.rb turns that into a test failure. It asserts that every cop file is registered exactly once, that no registration points at a missing file, that each registered constant matches the badge its class actually declares, and that requiring cookstyle still loads zero cop classes. Each of those was mutation-tested against a deliberately broken registration.

A missing registration is loud in two other places anyway: rake validate_config fails, and so does require "cookstyle" itself, since the config entry then names a cop RuboCop has never heard of.

unrecognized cop or department Chef/Correctness/InvalidChecksum found in config/cookstyle.yml

rake validate_config needed one fix. It used const_source_location to tell a Cookstyle cop from a Chefstyle cop, but on a pending autoload const_source_location returns the register_cop call site rather than the cop's own file. It now asks autoload? first, falling back to const_source_location for cops that are already loaded.

WRITING_RULES.md and DEVELOPER_GUIDE.md are updated: "the five files" is now six, with the register_cop line as step 2.

Requirements

None new. Cookstyle already pins RuboCop 1.90.0, well past the 1.89.0 that introduced LazyLoader.