ansible - broken role vars?

alternative_play.yml

# This one works with the include_/import_ interestingly
---
- hosts: localhost
  gather_facts: False
  connection: local
  vars:
    rolename: test2
  roles:
    - test1

main.yml

# roles/test1/tasks/main.yml
---
- debug:
    msg: "in {{ role_path }}"

- debug:
    msg: "{{ rolename }}"

# If either of these are uncommented, no tasks run, and you get an immediate
# ERROR! 'rolename' is undefined
#
#- import_role:
#    name: "{{ rolename }}"

#- include_role:
#    name: "{{ rolename }}"

output

PLAY [localhost] *********************************************************************************************************************

TASK [test1 : debug] *****************************************************************************************************************
ok: [localhost] => {
    "msg": "in /private/tmp/ansible/roles/test1"
}

TASK [test1 : debug] *****************************************************************************************************************
ok: [localhost] => {
    "msg": "test2"
}

PLAY RECAP ***************************************************************************************************************************
localhost                  : ok=2    changed=0    unreachable=0    failed=0

play.yml

# This one does not work
---
- hosts: localhost
  gather_facts: False
  connection: local
  roles:
    - { role: test1, rolename: test2 }