Bring back automatic yarn install run with deprecation notice

CHANGELOG.md

@@ -8,6 +8,11 @@ Changes since last non-beta release.
 
 _Please add entries here for your pull requests that are not yet released._
 
+### Fixed
+- Restores automatic installation of yarn packages removed in [#131](https://github.com/shakacode/shakapacker/pull/131), with added deprecation notice. [PR 140](https://github.com/shakacode/shakapacker/pull/140) by [tomdracz](https://github.com/tomdracz).
+
+  This will be again removed in Shakapacker v7 so you need to ensure you are installing yarn packages explicitly before the asset compilation, rather than relying on this behaviour through `asset:precompile` task (e.g. Capistrano deployment).
+
 ## [v6.4.0] - June 2, 2022
 ### Fixed
 - Fixed [Issue 123: Rails 7.0.3 - Webpacker configuration file not found when running rails webpacker:install (shakapacker v6.3)](https://github.com/shakacode/shakapacker/issues/123) in [PR 136: Don't enhance precompile if no config #136](https://github.com/shakacode/shakapacker/pull/136) by [justin808](https://github.com/justin808).

lib/tasks/webpacker/compile.rake

@@ -1,8 +1,16 @@
 $stdout.sync = true
 
+def yarn_install_available?
+  rails_major = Rails::VERSION::MAJOR
+  rails_minor = Rails::VERSION::MINOR
+
+  rails_major > 5 || (rails_major == 5 && rails_minor >= 1)
+end
+
 def enhance_assets_precompile
   # yarn:install was added in Rails 5.1
-  Rake::Task["assets:precompile"].enhance do |task|
+  deps = yarn_install_available? ? [] : ["webpacker:yarn_install"]
+  Rake::Task["assets:precompile"].enhance(deps) do |task|
     prefix = task.name.split(/#|assets:precompile/).first
 
     Rake::Task["#{prefix}webpacker:compile"].invoke
@@ -29,6 +37,6 @@ if Webpacker.config.webpacker_precompile?
   if Rake::Task.task_defined?("assets:precompile")
     enhance_assets_precompile
   else
-    Rake::Task.define_task("assets:precompile" => ["webpacker:compile"])
+    Rake::Task.define_task("assets:precompile" => ["webpacker:yarn_install", "webpacker:compile"])
   end
 end

lib/tasks/webpacker/yarn_install.rake

@@ -0,0 +1,24 @@
+namespace :webpacker do
+  desc "Support for older Rails versions. Install all JavaScript dependencies as specified via Yarn"
+  task :yarn_install do
+    warn <<~MSG.strip
+      Shakapacker - Automatic installation of yarn packages is deprecated
+      Automatic installation of yarn packages when assets are precompiled is deprecated and will be removed in Shakapacker v7.
+      Please ensure you are installing yarn packages explicitly before the asset compilation.
+    MSG
+
+    valid_node_envs = %w[test development production]
+    node_env = ENV.fetch("NODE_ENV") do
+      valid_node_envs.include?(Rails.env) ? Rails.env : "production"
+    end
+    Dir.chdir(Rails.root) do
+      yarn_flags =
+        if `yarn --version`.start_with?("1")
+          "--no-progress --frozen-lockfile"
+        else
+          "--immutable"
+        end
+      system({ "NODE_ENV" => node_env }, "yarn install #{yarn_flags}")
+    end
+  end
+end

lib/tasks/yarn.rake

@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+# Duplicate of the yarn tasks still present in Rails until Webpacker <5 have been deprecated
+
+namespace :yarn do
+  desc "Install all JavaScript dependencies as specified via Yarn"
+  task :install do
+    begin
+      # Install only production deps when for not usual envs.
+      valid_node_envs = %w[test development production]
+      node_env = ENV.fetch("NODE_ENV") do
+        valid_node_envs.include?(Rails.env) ? Rails.env : "production"
+      end
+
+      yarn_flags =
+        if `#{RbConfig.ruby} "#{Rails.root}/bin/yarn" --version`.start_with?("1")
+          "--no-progress --frozen-lockfile"
+        else
+          "--immutable"
+        end
+
+      system(
+        { "NODE_ENV" => node_env },
+        "#{RbConfig.ruby} \"#{Rails.root}/bin/yarn\" install #{yarn_flags}",
+        exception: true
+      )
+    rescue Errno::ENOENT
+      $stderr.puts "bin/yarn was not found."
+      $stderr.puts "Please run `bundle exec rails app:update:bin` to create it."
+      exit 1
+    end
+  end
+end
+
+# Run Yarn prior to Sprockets assets precompilation, so dependencies are available for use.
+if Rake::Task.task_defined?("assets:precompile") && File.exist?(Rails.root.join("bin", "yarn"))
+  warn <<~MSG.strip
+    Shakapacker - Automatic installation of yarn packages is deprecated
+    Automatic installation of yarn packages when assets are precompiled is deprecated and will be removed in Shakapacker v7.
+    Please ensure you are installing yarn packages explicitly before the asset compilation.
+  MSG
+
+  Rake::Task["assets:precompile"].enhance [ "yarn:install" ]
+end