Context is https://gerrit.wikimedia.org/r/c/operations/puppet/+/620726 where this code:
class profile::alertmanager::web (
String $vhost = lookup('profile::alertmanager::web::vhost', {'default_value' => "alerts.${facts['domain']}"}),
Boolean $enable_sso = lookup('profile::alertmanager::web::enable_sso', {'default_value' => true}),
Boolean $readonly = lookup('profile::alertmanager::web::readonly', {'default_value' => true}),
Array[Stdlib::Host] $prometheus_nodes = lookup('prometheus_nodes'),
) {Tricked wmf-style lint into thinking that ${facts['domain']} is a parameter:
18:22:01 wmf-style: total violations delta 1 18:22:01 NEW violations: 18:22:01 modules/profile/manifests/alertmanager/web.pp:8 wmf-style: Parameter 'facts['domain']' of class 'profile::alertmanager::web' has no call to lookup