Rails 5.1 Webpacker Cache Support

CHANGELOG.md

@@ -48,6 +48,7 @@
 
 * Vendor in libpq 5.12.1 for Heroku-18 (https://github.com/heroku/heroku-buildpack-ruby/pull/936)
 * Remove possibilities of false exceptions being raised by removing `BUNDLED WITH` from the `Gemfile.lock` (https://github.com/heroku/heroku-buildpack-ruby/pull/928)
+* Add webpacker support for Rails >= 5.1 (https://github.com/heroku/heroku-buildpack-ruby/pull/892)
 
 ## v206 (10/15/2019)
 

lib/language_pack.rb

@@ -13,7 +13,21 @@ def self.detect(*args)
     Instrument.instrument 'detect' do
       Dir.chdir(args.first)
 
-      pack = [ NoLockfile, Rails6, Rails5, Rails42, Rails41, Rails4, Rails3, Rails2, Rack, Ruby ].detect do |klass|
+      packs = [
+        NoLockfile,
+        Rails6,
+        Rails51,
+        Rails5,
+        Rails42,
+        Rails41,
+        Rails4,
+        Rails3,
+        Rails2,
+        Rack,
+        Ruby
+      ]
+
+      pack = packs.detect do |klass|
         klass.use?
       end
 
@@ -49,5 +63,6 @@ def self.detect(*args)
 require "language_pack/rails41"
 require "language_pack/rails42"
 require "language_pack/rails5"
+require "language_pack/rails51"
 require "language_pack/rails6"
 require "language_pack/no_lockfile"

lib/language_pack/rails51.rb

@@ -0,0 +1,93 @@
+require 'securerandom'
+require 'language_pack'
+require 'language_pack/rails5'
+
+class LanguagePack::Rails51 < LanguagePack::Rails5
+  ASSET_PATHS = %w[
+    public/packs
+    ~/.yarn-cache
+    ~/.cache/yarn
+  ]
+
+  ASSET_CACHE_PATHS = %w[
+    node_modules
+    tmp/cache/webpacker
+  ]
+
+  # @return [Boolean] true if it's a Rails 5.1.x app
+  def self.use?
+    instrument "rails51.use" do
+      rails_version = bundler.gem_version('railties')
+      return false unless rails_version
+      is_rails = rails_version >= Gem::Version.new('5.1.x')
+      return is_rails
+    end
+  end
+
+  private
+
+    def run_assets_precompile_rake_task
+      instrument "rails51.run_assets_precompile_rake_task" do
+        log("assets_precompile") do
+          if Dir.glob("public/assets/{.sprockets-manifest-*.json,manifest-*.json}", File::FNM_DOTMATCH).any?
+            puts "Detected manifest file, assuming assets were compiled locally"
+            return true
+          end
+
+          precompile = rake.task("assets:precompile")
+          return true unless precompile.is_defined?
+
+          topic("Preparing app for Rails asset pipeline")
+
+          load_asset_cache
+
+          precompile.invoke(env: rake_env)
+
+          if precompile.success?
+            log "assets_precompile", :status => "success"
+            puts "Asset precompilation completed (#{"%.2f" % precompile.time}s)"
+
+            puts "Cleaning assets"
+            rake.task("assets:clean").invoke(env: rake_env)
+
+            cleanup_assets_cache
+            store_asset_cache
+          else
+            precompile_fail(precompile.output)
+          end
+        end
+      end
+    end
+
+    def load_asset_cache
+      puts "Loading asset cache"
+      @cache.load_without_overwrite public_assets_folder
+      @cache.load default_assets_cache
+
+      paths = (self.class::ASSET_PATHS + self.class::ASSET_CACHE_PATHS)
+      paths.each { |path| @cache.load path }
+    end
+
+    def store_asset_cache
+      puts "Storing asset cache"
+      @cache.store public_assets_folder
+      @cache.store default_assets_cache
+
+      paths = (self.class::ASSET_PATHS + self.class::ASSET_CACHE_PATHS)
+      paths.each { |path| @cache.store path }
+    end
+
+    def cleanup
+      # does not call super because it would return if default_assets_cache was missing
+      #   child classes should call super and should not use a return statement
+      return if assets_compile_enabled?
+
+      puts "Removing non-essential asset cache directories"
+
+      FileUtils.remove_dir(default_assets_cache) if Dir.exist?(default_assets_cache)
+
+      self.class::ASSET_CACHE_PATHS.each do |path|
+        FileUtils.remove_dir(path) if Dir.exist?(path)
+      end
+    end
+end

lib/language_pack/rails6.rb

@@ -1,8 +1,8 @@
 require 'securerandom'
 require "language_pack"
-require "language_pack/rails5"
+require "language_pack/rails51"
 
-class LanguagePack::Rails6 < LanguagePack::Rails5
+class LanguagePack::Rails6 < LanguagePack::Rails51
   # @return [Boolean] true if it's a Rails 6.x app
   def self.use?
     instrument "rails6.use" do