Make "webpacker:yarn_install" task env aware (#1331)

* Make webpacker:yarn_install task env aware

When webpacker compiles in a non-production environment it's removing
node_modules which are dev dependencies. This is problematic on CI for
example because these dependencies may be required.

* Use alternative to Bundler.with_clean_env

This was failing on CI presumably because BUNDLE_GEMFILE was being
lost, causing the 4.2.x Gemfile tests to fail.

* Remove explicit production flag from Yarn Install task

If the NODE_ENV is set then Yarn will behave accordingly (e.g. skip
devDependencies if NODE_ENV=production).

Based on discussion:
rails/webpacker#1331 (comment)

* Use existing with_node_env helper

Author: odlp

lib/tasks/webpacker/yarn_install.rake

@@ -1,6 +1,6 @@
 namespace :webpacker do
   desc "Support for older Rails versions. Install all JavaScript dependencies as specified via Yarn"
   task :yarn_install do
-    system "yarn install --no-progress --frozen-lockfile --production"
+    system "yarn install --no-progress"
   end
 end

test/rake_tasks_test.rb

@@ -22,8 +22,42 @@ def test_rake_task_webpacker_check_binstubs
     refute_includes output, "webpack binstubs not found."
   end
 
+  def test_rake_webpacker_yarn_install_in_non_production_environments
+    assert_includes test_app_dev_dependencies, "right-pad"
+
+    Webpacker.with_node_env("test") do
+      Dir.chdir(test_app_path) do
+        `bundle exec rake webpacker:yarn_install`
+      end
+    end
+
+    assert_includes installed_node_module_names, "right-pad",
+                    "Expected dev dependencies to be installed"
+  end
+
+  def test_rake_webpacker_yarn_install_in_production_environment
+    Webpacker.with_node_env("production") do
+      Dir.chdir(test_app_path) do
+        `bundle exec rake webpacker:yarn_install`
+      end
+    end
+
+    refute_includes installed_node_module_names, "right-pad",
+                    "Expected only production dependencies to be installed"
+  end
+
   private
     def test_app_path
       File.expand_path("test_app", __dir__)
     end
+
+    def test_app_dev_dependencies
+      package_json = File.expand_path("package.json", test_app_path)
+      JSON.parse(File.read(package_json))["devDependencies"]
+    end
+
+    def installed_node_module_names
+      node_modules_path = File.expand_path("node_modules", test_app_path)
+      Dir.chdir(node_modules_path) { Dir.glob("*") }
+    end
 end

test/test_app/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "test_app",
+  "version": "1.0.0",
+  "main": "index.js",
+  "license": "MIT",
+  "private": true,
+  "dependencies": {
+    "left-pad": "^1.2.0"
+  },
+  "devDependencies": {
+    "right-pad": "^1.0.1"
+  }
+}

test/test_app/yarn.lock

@@ -0,0 +1,11 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+
+
+left-pad@^1.2.0:
+  version "1.2.0"
+  resolved "https://registry.yarnpkg.com/left-pad/-/left-pad-1.2.0.tgz#d30a73c6b8201d8f7d8e7956ba9616087a68e0ee"
+
+right-pad@^1.0.1:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/right-pad/-/right-pad-1.0.1.tgz#8ca08c2cbb5b55e74dafa96bf7fd1a27d568c8d0"