Request: An alternate FileTask that checks whether the file was made

I think the current implementation of the file task makes perfect sense: just trigger a series of actions based on a file's status, in case you don't necessarily want to actually produce that file.

However, in cases where you do want to produce that file, it would be nice to have a separate task type that supports that, i.e. fails if the task actions don't produce the file even when there are no exceptions thrown.

Example:

class Rake::RequiredFileTask < Rake::FileTask                  
  def execute(*args)                                          
    super(*args)                                              
    File.exists?(name) or raise "File #{name} was not created successfully"
  end                                                                      
end                                                                        

module Rake::DSL
  def required_file(*args, &block) # :doc:
    Rake::RequiredFileTask.define_task(*args, &block)
  end                                                
end

Then, if invoked as:

required_file 'a.out' do |t|
  # do nothing
end

an error would be thrown:

rake aborted!
File a.out was not created successfully

Empieza leyendo el comportamiento existente de Rake::FileTask y las Rake::DSL task definitions referenciadas en el issue. Verifica cómo se ejecuta una task action cuando no se producen excepciones y, después, confirma que el nuevo task type debe fallar cuando el archivo cuyo nombre lleva sigue sin existir, usando el required_file example proporcionado como comprobación de finalización.