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

Inizia leggendo il comportamento esistente di Rake::FileTask e le Rake::DSL task definitions citate nell’issue. Verifica come viene eseguita una task action quando non si verificano eccezioni, quindi conferma che il nuovo task type deve fallire quando il file di cui porta il nome è ancora assente, usando il required_file example fornito come controllo del completamento.