Support for functions for complex expressions

Archives Ansible Developer
1

Hi all,

Ansible has a lot of options, where combining and chaining filters is of great usage.
In certain cases the final result might become a bit hard to maintain if it is re-used in multiple places. E.g. take the following examples:

merged_list: “{{ (lookup(‘vars’, *query(‘varnames’, ‘^.+__merge_list$’)) + [testlist_initial_value]) | flatten(levels=1) }}”

merged_dict: “{{ lookup(‘vars’, *query(‘varnames’, ‘^.+__merge_dict$’)) | combine(testdict_initial_value, recursive=True, list_merge=‘append’) }}”

I couldn’t find anything about Ansible having this functionality, but is it an idea for adding functions/aliases to Ansible where often re-used expressions can be stored as a ‘function’ or ‘alias’ so the user can call it with the appropriate input arguments?

In case of the above e.g. defining the expressions somewhere and calling it as e.g.
{{ merge_dict(‘__merge_dict’, testdict_initial_value) }}

The user then only has to define the complex expression once, after which it can re-use the function in multiple places throughout the project.

Happy to hear any thoughts on this idea (or whether this is already possible).

Regards,
Roy

2

Jinja2 has this already, macros
https://jinja.palletsprojects.com/en/2.10.x/templates/#macros

3

Thanks for the link Brian!

I experimented a bit with macros but couldn’t find a working solution.
These are the lines I would like to have available in a macro: https://github.com/rlenferink/ansible-function-test/blob/9c83a40a29eb616a59b4da713771545a2aa44f32/playbook.yml#L15-L16

Knowing that this is called a macro, I found the following feature request: https://github.com/ansible/ansible/issues/36130
It is mentioned in the issue that the decision was made not to add such a feature.

I tried using the described workaround but wasn’t successful so far:

https://github.com/rlenferink/ansible-function-test/tree/macro-try

Honestly using a separate file for defining this macro and then importing it for every usage also feels a bit like a workaround (since this would not something I’d do once, more like in the 100+ occurrences area).

Do you know if there is an alternative to define and use macros within a playbook?
Is it maybe worth reevaluating the feature request for adding support for this?

Roy

4

Mostly i was thinking for the use of in templates, the only other
thing i can think of is using 'intermediate vars' to keep reusable
expressions and then creating their input when needed:

- play:
  vars:
      merged_list: "{{ (lookup('vars', *query('varnames',
merge_pattern$')) + [testlist_initial_value]) |
flatten(levels=merge_flatten_levels|default(1)) }}"
....

- name: also works with 'vars' in other scopes, using set_fact to
get 'static value'
   set_fact:
       mylist: '{{merged_list}}'
   vars:
     testlist_initial_value: [10,11]
     merge_pattern: '^.+_merge_list'
      a_merge_list: [1,2,3]
      b_merge_list: [4,5,6]