Marking tasks as :phony fails to prevent rebuild

The :phony task fails to prevent rebuild of FileTasks dependent on non-file tasks.

lib/rake/phony.rb

# Defines a :phony task that you can use as a dependency. This allows
# file-based tasks to use non-file-based tasks as prerequisites
# without forcing them to rebuild.
#
# See FileTask#out_of_date? and Task#timestamp for more info.

require 'rake'

task :phony

Rake::Task[:phony].tap do |task|
  def task.timestamp # :nodoc:
    Time.at 0
  end
end

Code reproducing bug

require 'rake/phony'

task :default => 'final.file'

file 'final.file' => ['source.file', :intermediate] do |f|
  touch f.name
end

# Marked as phony, so should not force FileTask to rebuild
task :intermediate => [:phony] do |t|
  puts "#{t.name} task"
end

Bug demo

$ touch source.file      # Create the source file
$ rake                   # Run Rake to build 'final.file'
intermediate task
touch final.file
$ rake                   # Rake should NOT rebuild, but does.     <<<<<<<<
intermediate task
touch final.file

Mentioned here

Start with lib/rake/phony.rb, then read FileTask#out_of_date? and Task#timestamp as the issue suggests. Run the provided reproduction with source.file and final.file, comparing the first and second rake runs. Done means a :phony prerequisite no longer causes the dependent FileTask to rebuild on the second run.