Ansible playbook conditionals - ansible

Question

I'm trying to put together playbook that works for both Windows and Linux. Now I'm trying to include roles in playbook that will be taken only if Windows or Linux, but it always complains about syntax. I'd appreciate any help on this as I've tried few different approaches and it always failed.
---
- hosts: all
gather_facts: no
pre_tasks:
- name: (localhost) make sure the known_hosts file is cleared
lineinfile:
path: ~/.ssh/known_hosts
state: absent
regexp: "^{{ ansible_host | replace('.', '\\.') }}.*$"
delegate_to: 127.0.0.1
- hosts: all
serial: 1
pre_tasks:
- name: (debug) print out some debug message to confirm inventory is properly set up
debug:
msg: "System inventory_hostname:{{ inventory_hostname }} ansible_host:{{ ansible_host }}"
- hosts: all
tasks:
- name: Install CA Trust Certs Windows
include_tasks: tasks\install-certs-windows.yml
when: ansible_os_family == 'Windows'
- name: Install CA Trust Certs Linux
include_tasks: tasks/install-certs-linux.yml
when: ansible_os_family != 'Windows'
roles:
- { role: ansible-role-runnersbasics, tags: ["basics"] }
- { role: ansible-role-docker, tags: ["docker"] }
- { role: ansible-role-gitlab-runner }
when: ansible_os_family == 'Windows'
Error:
ERROR! We were unable to read either as JSON nor YAML, these are the errors we got from each:
JSON: Expecting value: line 1 column 1 (char 0)
Syntax Error while loading YAML.
did not find expected key
The error appears to be in 'playbook.yml': line 33, column 5, but may
be elsewhere in the file depending on the exact syntax problem.
The offending line appears to be:
- { role: ansible-role-gitlab-runner }
when: ansible_os_family == 'Windows'
^ here
When removing curly braces from roles and moving when on the same level as roles
ERROR! We were unable to read either as JSON nor YAML, these are the errors we got from each:
JSON: Expecting value: line 1 column 1 (char 0)
Syntax Error while loading YAML.
mapping values are not allowed in this context
The error appears to be in 'playbook.yml': line 30, column 43, but may
be elsewhere in the file depending on the exact syntax problem.
The offending line appears to be:
roles:
role: ansible-role-runnersbasics, tags: ["basics"] }
^ here

Answer 1

In a word: DON'T
Alright, that's two words if you want to get picky about contractions.
Anyway.... Group your servers by OS, then work on them separately:
---
- hosts: Linux
gather_facts: no
# Do Linux stuff
- hosts: Windoze
serial: 1
# Do Windoze stuff

Answer 2

Resolved by using method that #Khaled provided (thanks again!)
roles:
- role: ansible-role-runnersbasics
tags: ["basics"]
when: ansible_os_family == 'Windows'