Problemas para usar haml y rails3

Question

Después de instalar rails3, tengo problemas al tratar de usar haml con él.

Tengo la joya actualizada instalada, y después de rails PROJECT_NAME, hice haml --rails en su raíz.

Aparentemente funcionó bien, ya que tengo la carpeta haml dentro de los complementos, init.rb, como era de esperar.

Pero cuando trato de rastrillo, o el servidor de rieles, me sale:

rake aborted! 
no such file to load -- haml 

Con --trace me sale esto:

** Invoke default (first_time) 
** Invoke test (first_time) 
** Execute test 
** Invoke test:units (first_time) 
** Invoke db:test:prepare (first_time) 
** Invoke db:abort_if_pending_migrations (first_time) 
** Invoke environment (first_time) 
** Execute environment 
rake aborted! 
no such file to load -- haml 
/usr/local/lib/ruby/gems/1.8/gems/activesupport-3.0.0.beta/lib/active_support/dependencies.rb:167:in `require' 
/usr/local/lib/ruby/gems/1.8/gems/activesupport-3.0.0.beta/lib/active_support/dependencies.rb:167:in `require' 
/usr/local/lib/ruby/gems/1.8/gems/activesupport-3.0.0.beta/lib/active_support/dependencies.rb:537:in `new_constants_in' 
/usr/local/lib/ruby/gems/1.8/gems/activesupport-3.0.0.beta/lib/active_support/dependencies.rb:167:in `require' 
RAILS_PROJECT_ROOT/vendor/plugins/haml/init.rb:5 
/usr/local/lib/ruby/gems/1.8/gems/railties-3.0.0.beta/lib/rails/plugin.rb:49 
/usr/local/lib/ruby/gems/1.8/gems/railties-3.0.0.beta/lib/rails/initializable.rb:25:in `instance_exec' 
/usr/local/lib/ruby/gems/1.8/gems/railties-3.0.0.beta/lib/rails/initializable.rb:25:in `run' 
/usr/local/lib/ruby/gems/1.8/gems/railties-3.0.0.beta/lib/rails/initializable.rb:55:in `run_initializers' 
/usr/local/lib/ruby/gems/1.8/gems/railties-3.0.0.beta/lib/rails/initializable.rb:54:in `each' 
/usr/local/lib/ruby/gems/1.8/gems/railties-3.0.0.beta/lib/rails/initializable.rb:54:in `run_initializers' 
/usr/local/lib/ruby/gems/1.8/gems/railties-3.0.0.beta/lib/rails/application.rb:71:in `initialize!' 
/usr/local/lib/ruby/gems/1.8/gems/railties-3.0.0.beta/lib/rails/application.rb:112:in `initialize_tasks' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `call' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `execute' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `each' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `execute' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:597:in `invoke_with_call_chain' 
/usr/local/lib/ruby/1.8/monitor.rb:242:in `synchronize' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:607:in `invoke_prerequisites' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:604:in `each' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:604:in `invoke_prerequisites' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:596:in `invoke_with_call_chain' 
/usr/local/lib/ruby/1.8/monitor.rb:242:in `synchronize' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:607:in `invoke_prerequisites' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:604:in `each' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:604:in `invoke_prerequisites' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:596:in `invoke_with_call_chain' 
/usr/local/lib/ruby/1.8/monitor.rb:242:in `synchronize' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:607:in `invoke_prerequisites' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:604:in `each' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:604:in `invoke_prerequisites' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:596:in `invoke_with_call_chain' 
/usr/local/lib/ruby/1.8/monitor.rb:242:in `synchronize' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:583:in `invoke' 
/usr/local/lib/ruby/gems/1.8/gems/railties-3.0.0.beta/lib/rails/test_unit/testing.rake:45 
/usr/local/lib/ruby/gems/1.8/gems/railties-3.0.0.beta/lib/rails/test_unit/testing.rake:43:in `collect' 
/usr/local/lib/ruby/gems/1.8/gems/railties-3.0.0.beta/lib/rails/test_unit/testing.rake:43 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `call' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `execute' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `each' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `execute' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:597:in `invoke_with_call_chain' 
/usr/local/lib/ruby/1.8/monitor.rb:242:in `synchronize' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:607:in `invoke_prerequisites' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:604:in `each' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:604:in `invoke_prerequisites' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:596:in `invoke_with_call_chain' 
/usr/local/lib/ruby/1.8/monitor.rb:242:in `synchronize' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:583:in `invoke' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2051:in `invoke_task' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `top_level' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `each' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2029:in `top_level' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2023:in `top_level' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2001:in `run' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:2068:in `standard_exception_handling' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:1998:in `run' 
/usr/local/lib/ruby/gems/1.8/gems/rake-0.8.7/bin/rake:31 
/usr/local/bin/rake:19:in `load' 
/usr/local/bin/rake:19 

Answer 1

Sólo tenía que poner en el gem "haml" Gemfile.

Answer 2

Otra causa común de esto es que Haml se instala como una gema en un entorno RVM, pero no en el que se está ejecutando la aplicación Rails.