Avoiding circular includes when using the profiles / roles pattern in Puppet

profile.pp

# Lesson: always use root scope when including a puppet module inside a profile or role file, e.g.:
#   include ::module

# Wrong way
class profile::mail::exim {
  include exim
  # This expands to current namespace first:
  #   include profile::mail::exim
  # Causing a circular dependency. Include does not throw duplicate errors, so this fails silently.
  # Intended 'exim' module is never loaded
}

# Wrong way, with classes
class profile::mail::exim {
  class { 'exim': }
  # This expands to current namespace first:
  #   include profile::mail::exim
  # Causing a circular dependency. This throws a duplicate error (profile::mail::exim)
  # Intended 'exim' module is never loaded
}

# Right way
class profile::mail::exim {
  include ::exim
  # Looks in root namespace, loads correct module:
  #   include /etc/puppet/module/exim/manifests/init.pp
}

# Right way, with classes
class profile::mail::exim {
  class { '::exim': }
  # Looks in root namespace, loads correct module:
  #   include /etc/puppet/module/exim/manifests/init.pp
}