gistfile1.txt

root@c312a1b640ef:/etc/puppetlabs/code/environments/production/manifests# cat ../hiera.yaml
---
version: 5
defaults:
hierarchy:
  - name: "node"
    path: node.yaml
  - name: "roles"
    mapped_paths:
      - roles
      - role
      - "%{role}.yaml"
  - name: "Other YAML hierarchy levels"
    paths:
      - "common.yaml"
      
root@c312a1b640ef:/etc/puppetlabs/code/environments/production/manifests# cat ../data/common.yaml

myhash:
  key1: value1
  key2: value2
  
root@c312a1b640ef:/etc/puppetlabs/code/environments/production/manifests# cat ../data/firstrole.yaml
lookup_options:
  myhash:
    merge:
      strategy: deep

myhash:
  role1: value1
  role2: value2
  
role1: role1
 
root@c312a1b640ef:/etc/puppetlabs/code/environments/production/manifests# cat ../data/secondrole.yaml
myhash:
  role1: value1
  role3: value3
  
role2: role2


root@c312a1b640ef:/etc/puppetlabs/code/environments/production/manifests# cat site.pp
$roles = lookup( 'roles', Array[String], 'unique', [], )
notice("roles: $roles")
$ret = lookup('myhash')
notice("myhash: $ret")

$role1 = lookup('role1')
$role2 = lookup('role2')
notice("role1 var: $role1")
notice("role2 var: $role2")


puppet-agent-5.3.5:
root@c312a1b640ef:/etc/puppetlabs/code/environments/production/manifests# puppet apply site.pp
Warning: Undefined variable 'roles'; \n   (file & line not available)
Notice: Scope(Class[main]): roles: [firstrole, secondrole]
Notice: Scope(Class[main]): myhash: {key1 => value1, key2 => value2, role1 => value1, role3 => value3, role2 => value2}
Notice: Scope(Class[main]): role1 var: role1
Notice: Scope(Class[main]): role2 var: role2
Notice: Compiled catalog for c312a1b640ef in environment production in 0.03 seconds
Notice: Applied catalog in 0.01 seconds

puppet-agent-5.5.1
root@c312a1b640ef:/etc/puppetlabs/code/environments/production/manifests# puppet apply site.pp
Warning: Undefined variable 'roles'; \n   (file & line not available)
Notice: Scope(Class[main]): roles: [firstrole, secondrole]
Notice: Scope(Class[main]): myhash: {role1 => value1, role2 => value2}
Notice: Scope(Class[main]): role1 var: role1
Notice: Scope(Class[main]): role2 var: role2
Notice: Compiled catalog for c312a1b640ef in environment production in 0.02 seconds
Notice: Applied catalog in 0.02 seconds

When putting the lookup_options in the common.yaml, the deep merge will happen also.