Support Jinja2 in dict keys

[jtyr]

ISSUE TYPE

Feature Pull Request

COMPONENT NAME

Templar

ANSIBLE VERSION

$ ansible --version
ansible 2.2.0.0
  config file = /etc/ansible/ansible.cfg
  configured module search path = Default w/o overrides

SUMMARY

This patch allows to use Jinja2 expressions in dictionary keys. Using this patch, the output of the following play

---
- hosts: all
  connection: local
  gather_facts: no
  vars:
   test_var: aaa
   test_list:
     - "{{ test_var }}"
     - "{{ test_var }}": bbb
  tasks:
    - debug:
       var: test_list

will result into this output:

TASK [debug] *******************************************************************
ok: [localhost] => {
    "test_list": [
        "aaa", 
        {
            "aaa": "bbb"
        }
    ]
}

instead of to this:

TASK [debug] *******************************************************************
ok: [localhost] => {
    "test_list": [
        "aaa", 
        {
            "{{ test_var }}": "bbb"
        }
    ]
}

fixes #19956

[dano0b]

Thank you for this pull request, hope it will be merged soon. I really missed this feature.

[dagwieers]

Seems useful, but I have to wrap my head around the implications though.

[jasperla]

I think this is an improvement over the current syntax that is required for Jinja2 expressions as keys:

key: key2  
var4: "{  
  '{{ key }}': value2
}"

[bcoca]

As discussed in IRC, there is an issue with interdependent keys or overridden keys happening at 'template time' will be subject to dictionary order and not predictable.

d['x'] = 1
d['y'] = 2
d['z'] = {{ d['x'] + d['y']}}
d[{{variable}}] = 11
variable = 'x'

Since d[variable] does not get resolved until consumption (not definition) the value of d['z'] depends on templating/dictionary order so it can be either 3 or 13 on different runs.

The 'working dict' has these keys until templated 'x', 'y', 'z', '{{variable}}' and we won't know that {{variable}} is 'x' until it is templated on consumption but the user has no way of guaranteeing that d['z'] is templated before or after d['{{variable}}'] is.

[jtyr]

After long IRC discussion with @bcoca I decided to close this PR as the proposed solution could lead to ugly implications.

For those interested in templating dict keys, please consider to use the solution described by @jasperla above.

[jtyr]

@jasperla Actually your workaround doesn't work. The result is a sting and not a dict. So there is absolutely no way how to template dict keys in Ansible ;o( Or am I wrong, @bcoca?

[angystardust]

@jtyr you're wrong. I was going mad trying to understand how to pass the key of the dict as a variable but after some failed tries, i managed to make it work using the following syntax:

networks: "{ '{{ net }}': {'gateway': '{{ gateway }}', 'network': '{{ vlan }}'}}"

[jtyr]

@angystardust Thanks for sharing the more complex example. Thanks to your example, I have just realized that I was mixing the block and the inline format which resulted to a string. The rule is that I have to use the inline format only:

# Inline format only - this results to dict
networks: "{
  '{{ net }}': {
    'gateway': '{{ gateway }}',
    'network': '{{ vlan }}'
  }
}"

# Mixture of the block and the inline format - this results to string
networks: "{
  '{{ net }}':
    'gateway': '{{ gateway }}',
    'network': '{{ vlan }}'
}"

[Yannick91]

As I explain in my thread I bump on the exact same issue (#41096).
The only way around this to use vars is by using the shell module and put variables in that command (curl command for example)

However, I fixed it for now with fix templates (for each environment) that I import as tasks in my main playbook.

Kind regards,

Yannick