Remove the yarn integrity check

The `yarn check` command has been removed in Yarn 2.0.

The yarn integrity check in Webpacker has commonly been a source of
confusion and frustration among developers. Its behavior at times does
not always match expectation.

Yarn's maintainer has described `yarn check` as buggy and discourages
its use: yarnpkg/yarn#6427 (comment)

This PR removes the yarn integrity check from the Webpacker railtie as
well as references to its setting in Webpacker::Configuration.

The Webpacker::Configuration#check_yarn_integrity= method has been left
in with a deprecation warning to avoid a breaking change.

README.md

@@ -28,7 +28,6 @@ in which case you may not even need the asset pipeline. This is mostly relevant
   - [Webpack Configuration](#webpack-configuration)
   - [Custom Rails environments](#custom-rails-environments)
   - [Upgrading](#upgrading)
-  - [Yarn Integrity](#yarn-integrity)
 - [Integrations](#integrations)
   - [React](./docs/integrations.md#react)
   - [Angular with TypeScript](./docs/integrations.md#angular-with-typescript)
@@ -300,26 +299,6 @@ yarn upgrade webpack-dev-server --latest
 yarn add @rails/webpacker@next
 ```
 
-### Yarn Integrity
-
-By default, in development, webpacker runs a yarn integrity check to ensure that all local JavaScript packages are up-to-date. This is similar to what bundler does currently in Rails, but for JavaScript packages. If your system is out of date, then Rails will not initialize. You will be asked to upgrade your local JavaScript packages by running `yarn install`.
-
-To turn off this option, you will need to change the default setting in `config/webpacker.yml`:
-
-```yaml
-# config/webpacker.yml
-development:
-  ...
-  # Verifies that correct packages and versions are installed by inspecting package.json, yarn.lock, and node_modules
-  check_yarn_integrity: false
-```
-
-You may also turn on this feature by adding the config option for any Rails environment in `config/webpacker.yml`:
-
-```yaml
-check_yarn_integrity: true
-```
-
 ## Integrations
 
 Webpacker ships with basic out-of-the-box integration. You can see a list of available commands/tasks by running `bundle exec rails webpacker`.

lib/install/config/webpacker.yml

@@ -6,7 +6,6 @@ default: &default
   public_root_path: public
   public_output_path: packs
   cache_path: tmp/cache/webpacker
-  check_yarn_integrity: false
   webpack_compile_output: true
 
   # Additional paths webpack should lookup modules
@@ -52,9 +51,6 @@ development:
   <<: *default
   compile: true
 
-  # Verifies that correct packages and versions are installed by inspecting package.json, yarn.lock, and node_modules
-  check_yarn_integrity: true
-
   # Reference: https://webpack.js.org/configuration/dev-server/
   dev_server:
     https: false

lib/webpacker/configuration.rb

@@ -64,11 +64,7 @@ def extensions
   end
 
   def check_yarn_integrity=(value)
-    data[:check_yarn_integrity] = value
-  end
-
-  def check_yarn_integrity?
-    fetch(:check_yarn_integrity)
+    warn "Webpacker::Configuration#check_yarn_integrity=(value) has been deprecated. The integrity check has been removed from Webpacker so changing this setting will have no effect."
   end
 
   def webpack_compile_output?

lib/webpacker/railtie.rb

@@ -7,49 +7,6 @@ class Webpacker::Engine < ::Rails::Engine
   # Allows Webpacker config values to be set via Rails env config files
   config.webpacker = ActiveSupport::OrderedOptions.new
 
-  initializer "webpacker.set_configs" do |app|
-    if app.config.webpacker.key?(:check_yarn_integrity)
-      Webpacker.config.check_yarn_integrity = app.config.webpacker.check_yarn_integrity
-    end
-  end
-
-  # ================================
-  # Check Yarn Integrity Initializer
-  # ================================
-  #
-  # development (on by default):
-  #
-  #    to turn off:
-  #     - edit config/environments/development.rb
-  #     - add `config.webpacker.check_yarn_integrity = false`
-  #
-  # production (off by default):
-  #
-  #    to turn on:
-  #     - edit config/environments/production.rb
-  #     - add `config.webpacker.check_yarn_integrity = true`
-  initializer "webpacker.yarn_check" do |app|
-    if File.exist?("yarn.lock") && Webpacker.config.config_path.exist? && Webpacker.config.check_yarn_integrity?
-      output = `yarn check --integrity && yarn check --verify-tree 2>&1`
-
-      unless $?.success?
-        $stderr.puts "\n\n"
-        $stderr.puts "========================================"
-        $stderr.puts "  Your Yarn packages are out of date!"
-        $stderr.puts "  Please run `yarn install --check-files` to update."
-        $stderr.puts "========================================"
-        $stderr.puts "\n\n"
-        $stderr.puts "To disable this check, please change `check_yarn_integrity`"
-        $stderr.puts "to `false` in your webpacker config file (config/webpacker.yml)."
-        $stderr.puts "\n\n"
-        $stderr.puts output
-        $stderr.puts "\n\n"
-
-        exit(1)
-      end
-    end
-  end
-
   initializer "webpacker.proxy" do |app|
     insert_middleware = Webpacker.config.dev_server.present? rescue nil
     if insert_middleware

test/test_app/config/application.rb

@@ -6,7 +6,6 @@ module TestApp
   class Application < ::Rails::Application
     config.secret_key_base = "abcdef"
     config.eager_load = true
-    config.webpacker.check_yarn_integrity = false
     config.active_support.test_order = :sorted
   end
 end