Methods defined in Rakefile added to every object, via Kernel

output.txt

$ rake testing:test
Methods on Kernel:
[:foo_from_rake_namespace, :bar_from_rake_namespace, :foo_from_rake_top_level]

Methods on class (and source locations):
:foo_from_rake_namespace => ["/Users/tim/Source/dry-rb/_bugs/rake_test/Rakefile", 9]
:bar_from_rake_namespace => ["/Users/tim/Source/dry-rb/_bugs/rake_test/Rakefile", 13]
:foo_from_rake_top_level => ["/Users/tim/Source/dry-rb/_bugs/rake_test/Rakefile", 4]

Rakefile

class MyClass
end

def foo_from_rake_top_level
  "foo"
end

namespace :testing do
  def foo_from_rake_namespace
    "foo"
  end

  def bar_from_rake_namespace
    "bar"
  end

  task :test do
    puts "Methods on Kernel:"
    p Kernel.private_methods.grep(/from_rake/)
    puts

    puts "Methods on class (and source locations):"
    my_obj = MyClass.new

    my_obj.private_methods.grep(/from_rake/).each { |meth|
      puts "#{meth.inspect} => #{my_obj.method(meth).source_location.inspect}"
    }
  end
end

OK, it turns out this is nothing to do with Rake, it's just plain Ruby behaviour.

Define a method in the global namespace, and it goes onto Kernel, and therefore becomes a private method for every object created henceforth.

class MyClass
end

def top_level_method
  "hi"
end

p MyClass.new.private_methods.grep(/top_level/)
# => [:top_level_method]

tl;dr don't define unscoped methods in Rakefiles! 😬