How to prevent Jinja2 substitution in Ansible

I goal is to replace all the {{ and }} with {% raw %}{{ and }}{% endraw %} in all my markdown notes so that my hexo plugin won't attempt to template when rendering.

My code is:

- name: Get file list of post files
  find:
    paths: "{{ hexo_data_post_file_dir }}"
  register: hexo_data_post_file_list

- name: Replace special char
  replace:
    path: "{{ item[0]['path'] }}"
    regexp: "{{ item[1]['pattern'] }}"
    replace: "{{ item[1]['string'] }}"
  with_nested:
    - "{{ hexo_data_post_file_list['files'] }}"
    - - pattern: "{{  '{{' }}"
        string: "{{ '{% raw %}{{' }}"
      - pattern: "{{ '}}' }}"
        string: "{{ '}}{% endraw %}' }}"

Despite I used "{{ '{{' }}" to ask jinja not to render {{, I still get error:

TASK [setup_docker_hexo : Replace special char] ********************************************************************************************************************************************
Tuesday 27 December 2022  11:58:56 +0800 (0:00:00.491)       0:00:13.572 ******
fatal: [uranus-debian]: FAILED! => {"msg": "template error while templating string: unexpected 'end of template'. String: {{. unexpected 'end of template'"}

Solution

^{Given the file
shell> cat test.txt.j2
{{ test_var }}}

Declare the strings unsafe to block templating. For example,

  my_files:
    - "{{ playbook_dir }}/test.txt.j2"

  my_regex:
    - pattern: !unsafe '{{ '
      string: !unsafe '{% raw %}{{ {% endraw %}'
    - pattern: !unsafe ' }}'
      string: !unsafe '{% raw %} }}{% endraw %}'

Test the expansion

    - debug:
        msg: "{{ item }}"
      with_nested:
        - "{{ my_files }}"
        - "{{ my_regex }}"

gives

^{TASK [debug] *********************************************************************************
ok: [localhost] => (item=['/export/scratch/tmp7/test-117/test.txt.j2', {'pattern': '{{ ', 'string': '{% raw %}{{ {% endraw %}'}]) =>
msg:
- /export/scratch/tmp7/test-117/test.txt.j2
- pattern: '{{ '
string: '{% raw %}{{ {% endraw %}'
ok: [localhost] => (item=['/export/scratch/tmp7/test-117/test.txt.j2', {'pattern': ' }}', 'string': '{% raw %} }}{% endraw %}'}]) =>
msg:
- /export/scratch/tmp7/test-117/test.txt.j2
- pattern: ' }}'
string: '{% raw %} }}{% endraw %}'}

Replace the patterns

    - replace:
        path: "{{ item.0 }}"
        regexp: "{{ item.1.pattern }}"
        replace: "{{ item.1.string }}"
      with_nested:
        - "{{ my_files }}"
        - "{{ my_regex }}"
    - debug:
        msg: "{{ lookup('file', my_files.0) }}"
    - debug:
        msg: "{{ lookup('template', my_files.0) }}"

gives

^{TASK [debug] *********************************************************************************
ok: [localhost] =>
msg: '{% raw %}{{ {% endraw %}test_var{% raw %} }}{% endraw %}'

TASK [debug] *********************************************************************************
ok: [localhost] =>
msg: |-
{{ test_var }}}

Declare the variable

  my_file: "{{ playbook_dir }}/test.txt"
  test_var: foo bar

and use the template

    - template:
        src: "{{ my_files.0 }}"
        dest: "{{ my_file }}"
    - debug:
        msg: "{{ lookup('file', my_file) }}"
    - debug:
        msg: "{{ lookup('template', my_file) }}"

gives

^{TASK [debug] *********************************************************************************
ok: [localhost] =>
msg: '{{ test_var }}'

TASK [debug] *********************************************************************************
ok: [localhost] =>
msg: |-
foo bar

Notes

Example of a complete playbook for testing

- hosts: localhost

vars:

my_files:
- "{{ playbook_dir }}/test.txt.j2"

my_regex:
- pattern: !unsafe '{{'
string: !unsafe '{% raw %}{{{% endraw %}'
- pattern: !unsafe '}}'
string: !unsafe '{% raw %}}}{% endraw %}'

my_file: "{{ playbook_dir }}/test.txt"
test_var: foo bar

tasks:

- debug:
msg: "{{ item }}"
with_nested:
- "{{ my_files }}"
- "{{ my_regex }}"

- replace:
path: "{{ item.0 }}"
regexp: "{{ item.1.pattern }}"
replace: "{{ item.1.string }}"
with_nested:
- "{{ my_files }}"
- "{{ my_regex }}"
- debug:
msg: "{{ lookup('file', my_files.0) }}"
- debug:
msg: "{{ lookup('template', my_files.0) }}"

- template:
src: "{{ my_files.0 }}"
dest: "{{ my_file }}"
- debug:
msg: "{{ lookup('file', my_file) }}"
- debug:
msg: "{{ lookup('template', my_file) }}"

The playbook is not idempotent!}