Extract class Standalone

I wanted to fix some minor Rubocop issues and got confused by
'#{ruby_engine}/#{ruby_version}'. I managed to confuse two other people
working on bundler as well, so I decided to refactor the part around it.
I wanted to encapsulate the file creation, so it's (even) more obvious
from the context that another ruby file is created. So having an
uninterpolated string with interpolation syntax in it isn't so unusual.
To be extra sure I added a comment here as Rubocop might lead others to
the same spot.

I found that Standalone works quite well as its own object. While
extracting the class I shortened some expressions and extracted methods
that made sense as a unit to me. I ended up with a generate method that
only deals with file output.

What I think might be controversial:
* The tendency to use methods instead of variables for small things like
  version_dir and bundler_path:
  I think it's easier to understand because methdos are "read_only",
  while values of variables might change during code execution.
* Array(spec.require_paths) instead of
  "next if spec.require_paths.nil? # builtin gems".
  We lose the comment here, but I thought Array was more concise and
  that the information about the type of gems isn't crucial here.
* flat_map { map { ... } } instead of "collecting" in paths
  My perspective is that paths is the result of a transformation of
  @specs and that's best expressed by using map. It's also shorter.

2 files changed, 50 insertions, 39 deletions

diff --git a/lib/bundler/installer.rb b/lib/bundler/installer.rb
index 923fbd1faf..1fd0b85dd9 100644
--- a/lib/bundler/installer.rb
+++ b/lib/bundler/installer.rb
@@ -2,6 +2,7 @@ require "erb"
 require "rubygems/dependency_installer"
 require "bundler/worker"
 require "bundler/installer/parallel_installer"
+require "bundler/installer/standalone"
 
 module Bundler
   class Installer < Environment
@@ -68,7 +69,7 @@ module Bundler
       install(options)
 
       lock unless Bundler.settings[:frozen]
-      generate_standalone(options[:standalone]) if options[:standalone]
+      Standalone.new(options[:standalone], @definition).generate if options[:standalone]
     end
 
     def install_gem_from_spec(spec, standalone = false, worker = 0, force = false)
@@ -209,44 +210,6 @@ module Bundler
       end
     end
 
-    def generate_standalone(groups)
-      standalone_path = Bundler.settings[:path]
-      bundler_path = File.join(standalone_path, "bundler")
-      SharedHelpers.filesystem_access(bundler_path) do |p|
-        FileUtils.mkdir_p(p)
-      end
-
-      paths = []
-
-      if groups.empty?
-        specs = @definition.requested_specs
-      else
-        specs = @definition.specs_for groups.map(&:to_sym)
-      end
-
-      specs.each do |spec|
-        next if spec.name == "bundler"
-        next if spec.require_paths.nil? # builtin gems
-
-        spec.require_paths.each do |path|
-          full_path = Pathname.new(path).absolute? ? path : File.join(spec.full_gem_path, path)
-          gem_path = Pathname.new(full_path).relative_path_from(Bundler.root.join(bundler_path))
-          paths << gem_path.to_s.sub("#{Bundler.ruby_version.engine}/#{RbConfig::CONFIG["ruby_version"]}", '#{ruby_engine}/#{ruby_version}')
-        end
-      end
-
-      File.open File.join(bundler_path, "setup.rb"), "w" do |file|
-        file.puts "require 'rbconfig'"
-        file.puts "# ruby 1.8.7 doesn't define RUBY_ENGINE"
-        file.puts "ruby_engine = defined?(RUBY_ENGINE) ? RUBY_ENGINE : 'ruby'"
-        file.puts "ruby_version = RbConfig::CONFIG[\"ruby_version\"]"
-        file.puts "path = File.expand_path('..', __FILE__)"
-        paths.each do |path|
-          file.puts %{$:.unshift "\#{path}/#{path}"}
-        end
-      end
-    end
-
     def install_in_parallel(size, standalone, force = false)
       ParallelInstaller.call(self, specs, size, standalone, force)
     end
diff --git a/lib/bundler/installer/standalone.rb b/lib/bundler/installer/standalone.rb
new file mode 100644
index 0000000000..24a4183ea2
--- /dev/null
+++ b/lib/bundler/installer/standalone.rb
@@ -0,0 +1,48 @@
+module Bundler
+  class Standalone
+    def initialize(groups, definition)
+      @specs = groups.empty? ? definition.requested_specs : definition.specs_for(groups.map(&:to_sym))
+    end
+
+    def generate
+      SharedHelpers.filesystem_access(bundler_path) do |p|
+        FileUtils.mkdir_p(p)
+      end
+      File.open File.join(bundler_path, "setup.rb"), "w" do |file|
+        file.puts "require 'rbconfig'"
+        file.puts "# ruby 1.8.7 doesn't define RUBY_ENGINE"
+        file.puts "ruby_engine = defined?(RUBY_ENGINE) ? RUBY_ENGINE : 'ruby'"
+        file.puts "ruby_version = RbConfig::CONFIG[\"ruby_version\"]"
+        file.puts "path = File.expand_path('..', __FILE__)"
+        paths.each do |path|
+          file.puts %{$:.unshift "\#{path}/#{path}"}
+        end
+      end
+    end
+
+    private
+
+    def paths
+      @specs.flat_map do |spec|
+        next if spec.name == "bundler"
+        Array(spec.require_paths).map do |path|
+          gem_path(path, spec).sub(version_dir, '#{ruby_engine}/#{ruby_version}')
+          # This is a static string intentionally. It's interpolated at a later time.
+        end
+      end
+    end
+
+    def version_dir
+      "#{Bundler.ruby_version.engine}/#{RbConfig::CONFIG["ruby_version"]}"
+    end
+
+    def bundler_path
+      File.join(Bundler.settings[:path], "bundler")
+    end
+
+    def gem_path(path, spec)
+      full_path = Pathname.new(path).absolute? ? path : File.join(spec.full_gem_path, path)
+      Pathname.new(full_path).relative_path_from(Bundler.root.join(bundler_path)).to_s
+    end
+  end
+end