Quotes style exception: single quotes don't work for escape characters

[SiqingYu]

As https://github.com/whitecloud/ansible-styleguide#quotes stated, single quotes should be preferred for strings; double quotes are only allowed if embedded in Jinja templates. But it seems that I found an exception from my work where only double quotes work, but single quotes do not.

# test.yml
---

- name: test special quote cases
  hosts: localhost
  vars:
    tabbed_strings:
      - "aaa\t111"
      - "bbb\t222"
      - "ccc\t333"
  tasks:
    - name: double quotes work
      debug:
        msg: "{{ item.split('\t')[0] }}" 
      loop: "{{ tabbed_strings }}"

    - name: single quotes don't work
      debug:
        msg: '{{ item.split("\t")[0] }}'
      loop: '{{ tabbed_strings }}'

Output:

➜ ansible-playbook test.yml -v
Using /home/sqyu/code/greatdb-ansible/ansible.cfg as config file

PLAY [test special quote cases] ***********************************************************************************************************************************************************************************

TASK [double quotes work] *****************************************************************************************************************************************************************************************
ok: [localhost] => (item=aaa    111) => 
  msg: aaa
ok: [localhost] => (item=bbb    222) => 
  msg: bbb
ok: [localhost] => (item=ccc    333) => 
  msg: ccc

TASK [single quotes don't work] ***********************************************************************************************************************************************************************************
ok: [localhost] => (item=aaa    111) => 
  msg: "aaa\t111"
ok: [localhost] => (item=bbb    222) => 
  msg: "bbb\t222"
ok: [localhost] => (item=ccc    333) => 
  msg: "ccc\t333"

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

The output shows that the split() function doesn't work for single-quoted strings.

Why do I use double quotes for tabbed_strings in the above case? Because I found it is how Ansible's register produces strings from stdout.

The official Ansible YAML syntax documentation stated that single quotes don't work with escape characters.