Merge pull request #3494 from sinisterchipmunk/usage-erb

treat USAGE as an ERB template

railties/lib/rails/generators/base.rb

@@ -34,7 +34,7 @@ module Rails
         usage = source_root && File.expand_path("../USAGE", source_root)
 
         @desc ||= if usage && File.exist?(usage)
-          File.read(usage)
+          ERB.new(File.read(usage)).result(binding)
         else
           "Description:\n    Create #{base_name.humanize.downcase} files for #{generator_name} generator."
         end

railties/test/fixtures/lib/generators/usage_template/USAGE

@@ -0,0 +1 @@
+:: <%= 1 + 1 %> ::

railties/test/fixtures/lib/generators/usage_template/usage_template_generator.rb

@@ -0,0 +1,5 @@
+require 'rails/generators'
+
+class UsageTemplateGenerator < Rails::Generators::Base
+  source_root File.expand_path("templates", File.dirname(__FILE__))
+end

railties/test/generators_test.rb

@@ -201,4 +201,10 @@ class GeneratorsTest < Rails::Generators::TestCase
     mspec = Rails::Generators.find_by_namespace :fixjour
     assert mspec.source_paths.include?(File.join(Rails.root, "lib", "templates", "fixjour"))
   end
+  
+  def test_usage_with_embedded_ruby
+    require File.expand_path("fixtures/lib/generators/usage_template/usage_template_generator", File.dirname(__FILE__))
+    output = capture(:stdout) { Rails::Generators.invoke :usage_template, ['--help'] }
+    assert_match /:: 2 ::/, output
+  end
 end