Add Next Gemfile Support

Closes #1

README.md

@@ -48,6 +48,17 @@ For more information about using Ruby and buildpacks on Heroku, see these Dev Ce
 
 To use this buildpack, fork it on Github.  Push up changes to your fork, then create a test app with `--buildpack <your-github-url>` and push to it.
 
+
+## Next Rails
+
+This buildpack supports next Rails versions, to configure it follow the steps below:
+
+1. Make sure your app can boot with the next Rails version locally.
+2. Go to the Settings tab of your Heroku app, and add the `BUNDLE_GEMFILE` config var with `Gemfile.next` as a value.
+3. Go to the Buildpacks section and remove the `heroku/ruby` buildpack from your app and add `https://github.com/fastruby/heroku-buildpack-ruby#add_gemfile_next_support`
+4. Deploy your app to Heroku.
+5. The Next Rails version should be installed and your app should boot.
+
 ### Testing
 
 The tests on this buildpack are written in Rspec to allow the use of

lib/language_pack/helpers/bundler_wrapper.rb

@@ -101,7 +101,7 @@ def initialize(version_hash, major_minor)
   def initialize(options = {})
     @bundler_tmp          = Pathname.new(Dir.mktmpdir)
     @fetcher              = options[:fetcher]      || LanguagePack::Fetcher.new(LanguagePack::Base::VENDOR_URL) # coupling
-    @gemfile_path         = options[:gemfile_path] || Pathname.new("./Gemfile")
+    @gemfile_path         = options[:gemfile_path] || Pathname.new(env("BUNDLE_GEMFILE") || "./Gemfile")
     @gemfile_lock_path    = Pathname.new("#{@gemfile_path}.lock")
 
     @version = self.class.detect_bundler_version(contents: @gemfile_lock_path.read(mode: "rt"))
@@ -223,7 +223,7 @@ def needs_ruby_global_append_path?
   end
 
   def bundler_version_escape_valve!
-    topic("Removing BUNDLED WITH version in the Gemfile.lock")
+    topic("Removing BUNDLED WITH version in the #{@gemfile_lock_path}")
     contents = File.read(@gemfile_lock_path, mode: "rt")
     File.open(@gemfile_lock_path, "w") do |f|
       f.write contents.sub(/^BUNDLED WITH$(\r?\n)   (?<major>\d+)\.\d+\.\d+/m, '')

lib/language_pack/ruby.rb

@@ -144,7 +144,7 @@ def build
       build_bundler
       # TODO post_bundler might need to be done in a new layer
       bundler.clean
-      gem_layer.metadata[:gems] = Digest::SHA2.hexdigest(File.read("Gemfile.lock"))
+      gem_layer.metadata[:gems] = Digest::SHA2.hexdigest(File.read(gemfile_lock_path))
       gem_layer.metadata[:stack] = @stack
       gem_layer.metadata[:ruby_version] = run_stdout(%q(ruby -v)).strip
       gem_layer.metadata[:rubygems_version] = run_stdout(%q(gem -v)).strip
@@ -779,7 +779,7 @@ def build_bundler
       if bundler.windows_gemfile_lock?
         log("bundle", "has_windows_gemfile_lock")
 
-        File.unlink("Gemfile.lock")
+        File.unlink(gemfile_lock_path)
         ENV.delete("BUNDLE_DEPLOYMENT")
 
         warn(<<~WARNING, inline: true)
@@ -816,7 +816,7 @@ def build_bundler
 
         # we need to set BUNDLE_CONFIG and BUNDLE_GEMFILE for
         # codon since it uses bundler.
-        env_vars["BUNDLE_GEMFILE"] = "#{pwd}/Gemfile"
+        env_vars["BUNDLE_GEMFILE"] = "#{pwd}/#{gemfile_path}"
         env_vars["BUNDLE_CONFIG"] = "#{pwd}/.bundle/config"
         env_vars["CPATH"] = noshellescape("#{yaml_include}:$CPATH")
         env_vars["CPPATH"] = noshellescape("#{yaml_include}:$CPPATH")
@@ -1350,4 +1350,16 @@ def purge_bundler_cache(stack = nil)
     # need to reinstall language pack gems
     install_bundler_in_app(slug_vendor_base)
   end
+
+  def current_gemfile
+    env("BUNDLE_GEMFILE") || "Gemfile"
+  end
+
+  def gemfile_path
+    Pathname.new(current_gemfile)
+  end
+
+  def gemfile_lock_path
+    Pathname.new("#{current_gemfile}.lock")
+  end
 end