ensure rake tasks produce helpful error messages for node dependency issues

lib/tasks/eslint.rake

 unless Rails.env.production?
   desc "GitLab | Run ESLint"
-  task :eslint do
-    system("yarn", "run", "eslint")
+  task eslint: ['yarn:check'] do
+    sh "yarn run eslint" do |ok, res|
+      abort('rake eslint failed') unless ok
+    end
   end
 end
-

lib/tasks/gitlab/assets.rake

 namespace :gitlab do
   namespace :assets do
     desc 'GitLab | Assets | Compile all frontend assets'
-    task :compile do
-      Rake::Task['assets:precompile'].invoke
-      Rake::Task['webpack:compile'].invoke
-      Rake::Task['gitlab:assets:fix_urls'].invoke
-    end
+    task compile: [
+      'yarn:check',
+      'assets:precompile',
+      'webpack:compile',
+      'gitlab:assets:fix_urls'
+    ]
 
     desc 'GitLab | Assets | Clean up old compiled frontend assets'
-    task :clean do
-      Rake::Task['assets:clean'].invoke
-    end
+    task clean: ['assets:clean']
 
     desc 'GitLab | Assets | Remove all compiled frontend assets'
-    task :purge do
-      Rake::Task['assets:clobber'].invoke
-    end
+    task purge: ['assets:clobber']
+
+    desc 'GitLab | Assets | Uninstall frontend dependencies'
+    task purge_modules: ['yarn:clobber']
 
     desc 'GitLab | Assets | Fix all absolute url references in CSS'
     task :fix_urls do

lib/tasks/karma.rake

 unless Rails.env.production?
-  Rake::Task['karma'].clear if Rake::Task.task_defined?('karma')
-
   namespace :karma do
     desc 'GitLab | Karma | Generate fixtures for JavaScript tests'
     RSpec::Core::RakeTask.new(:fixtures) do |t|
@@ -10,7 +8,7 @@ unless Rails.env.production?
     end
 
     desc 'GitLab | Karma | Run JavaScript tests'
-    task :tests do
+    task tests: ['yarn:check'] do
       sh "yarn run karma" do |ok, res|
         abort('rake karma:tests failed') unless ok
       end
@@ -18,8 +16,5 @@ unless Rails.env.production?
   end
 
   desc 'GitLab | Karma | Shortcut for karma:fixtures and karma:tests'
-  task :karma do
-    Rake::Task['karma:fixtures'].invoke
-    Rake::Task['karma:tests'].invoke
-  end
+  task karma: ['karma:fixtures', 'karma:tests']
 end

lib/tasks/yarn.rake

+
+namespace :yarn do
+  desc 'Ensure Yarn is installed'
+  task :available do
+    unless system('yarn --version', out: File::NULL)
+      warn(
+        'Error: Yarn executable was not detected in the system.'.color(:red),
+        'Download Yarn at https://yarnpkg.com/en/docs/install'.color(:green)
+      )
+      abort
+    end
+  end
+
+  desc 'Ensure Node dependencies are installed'
+  task check: ['yarn:available'] do
+    unless system('yarn check --ignore-engines', out: File::NULL)
+      warn(
+        'Error: You have unmet dependencies. (`yarn check` command failed)'.color(:red),
+        'Run `yarn install` to install missing modules.'.color(:green)
+      )
+      abort
+    end
+  end
+
+  desc 'Install Node dependencies with Yarn'
+  task install: ['yarn:available'] do
+    unless system('yarn install --force --pure-lockfile --ignore-engines')
+      abort 'Error: Unable to install node modules.'.color(:red)
+    end
+  end
+
+  desc 'Remove Node dependencies'
+  task :clobber do
+    warn 'Purging ./node_modules directory'.color(:red)
+    FileUtils.rm_rf 'node_modules'
+  end
+end
+
+desc 'Install Node dependencies with Yarn'
+task yarn: ['yarn:install']