[root@ip-172-31-20-152 modules]# cat foo/manifests/params.pp
class foo::params {
  $bar = 'baz'
}

[root@ip-172-31-20-152 modules]# cat foo/manifests/something.pp
class foo::something {
  # this does NOT resolve up to $foo::bar because it has no parent class
  notify { $bar: }
}

[root@ip-172-31-20-152 modules]# cat foo/manifests/init.pp
class foo inherits foo::params {
  notify { $bar: }

  include foo::something # Scope does NOT follow down to this class
}

[root@ip-172-31-20-152 modules]# puppet apply -e 'include foo'
Warning: Unknown variable: 'bar'. at /opt/puppetlabs/puppet/modules/foo/manifests/something.pp:3:12
Error: Evaluation Error: Missing title. The title expression resulted in undef at /opt/puppetlabs/puppet/modules/foo/manifests/something.pp:3:12 on node ip-172-31-20-152.us-west-2.compute.internal[root@ip-172-31-20-152 modules]# puppet --version
5.1.0