Multiple Pass Variable Expansion

[Mike Ray]

I found this post (http://stackoverflow.com/questions/29276198/ansible-how-to-construct-a-variable-from-another-variable-and-then-fetch-its-v) and was hoping to find a way to cope with it.

To sum up though, basically I have a situation where I'd like to get the value of a value of a variable.

e.g.:

defaults/main.yml:
---

Ubuntu:
 14:
  packages:
    install:
      - iptables
    remove:

      - mlocate

CentOS:
 6:

  packages:
    install:
      - emacs
    remove: [ ]

packages:
 install: "{{ ansible_distribution }}.{{ ansible_distribution_major_version }}.packages.remove|default([ ]) | union(my_packages.remove|default([ ]))"
 remove: "{{ ansible_distribution }}.{{ ansible_distribution_major_version }}.packages.remove|default([ ]) | union(my_packages.remove|default([ ]))"

However, this is assigning a string value to packages.install and packages.remove not the actual list, so I have to force variable expansion. This works for tasks:

 

tasks/main.yml:
---
 - name: install packages
   action: "{{anisble_pkg_mgr }} state=present name={{ item }}"
   with_items: "{{ packages.install }}"

But it does not work for templating:

templates/test.j2:
--- 
{{ packages.install }}

...

TASK: [template src=t.yml dest=/tmp/] ***************************************** 

--- before: /tmp/t.yml

+++ after: /home/ansible-playbooks/t.yml

@@ -0,0 +1,43 @@

+Ubuntu.14.packages.install

If I could force or enable multiple pass variable expansion on the definition of packages.install (i.e. expand {{ ansible_distribution }} and {{ ansible_distribution_major_version }}  and then get the value of "Ubuntu.14.packages.install" and assign that list to packages.install ), I wouldn't need to force the expansion on the task and could also use the resulting list in templates like normal.

There are only two ways of getting around this as I see it, but neither are ideal. I could make tasks use a distribution specific when clause, but those are a pain as it ends up with a lot of duplicated work. I could also make distribution specific vars files and have an include_vars task, but this is bad as include_vars would prevent variables from being overridden in playbooks that used this role as a dependency. 

Is this possible? Or does someone have a suggestion about how to cope with this situation that I haven't considered?