referencing variables from defaults/main.yml in ansible role

I have a role setup as follows

roles/test/task/main.yml

- name: Generate people files
  template: src=test.j2 dest=/tmp/{{ item.name }}.cfg
  loop: "{{people}}"

roles/test/template/test.j2

First Var: {{ item.var1 }}
Second Var: {{ item.var2 }}

roles/test/vars/main.yml

---
people:
        - name: TheSimpsons
          var1: homer
          var2: simpson

        - name: StarWars
          var1: han
          var2: solo

roles/test/defaults/main.yml

people:
   - var2: skywalker

my playbook

 - hosts: localhost
   roles:
    - test

When I run my playbook everything works as expect. I get two new files in /tmp with the correct text. However if I remove this var2 line from my vars/main.yml file...

          var2: solo

I would expect the var2 value from my defaults/main.yml to show up in the output, but all I get is this error

failed: [localhost] (item={u'var1': u'han', u'name': u'StarWars'}) => {
    "changed": false,
    "item": {
        "name": "StarWars",
        "var1": "han"
    },
    "msg": "AnsibleUndefinedVariable: 'dict object' has no attribute 'var2'"
}

I have tried formatting my defaults/main.yml about 10 different ways but get the same error each time.

If I setup a test that doesn't loop and defaults/main.yml and vars/main.yml are flat "key: value" pairs I can get it to pull values from defaults/main/yml just fine.

Something about the looping I'm just not getting. What am I doing wrong?

Solution

There are more options on how to combine the lists' items. For example, rename the defaults, e.g.

people_defaults:
   - var2: skywalker

Rename the vars too and create the list

people_vars:
  - name: TheSimpsons
    var1: homer
    var2: simpson
  - name: StarWars
    var1: than
people: "{{ people_defaults|product(people_vars)|map('combine')|list }}"

gives

people:
  - name: TheSimpsons
    var1: homer
    var2: simpson
  - name: StarWars
    var1: han
    var2: skywalker

^{Details of the role
shell> tree roles/test/
roles/test/
├── defaults
│ └── main.yml
├── tasks
│ └── main.yml
└── vars
└── main.yml

3 directories, 3 files

shell> cat roles/test/defaults/main.yml
people_defaults:
- var2: skywalker

shell> cat roles/test/vars/main.yml
people_vars:
- name: TheSimpsons
var1: homer
var2: simpson
- name: StarWars
var1: han
people: "{{ people_defaults|product(people_vars)|map('combine')|list }}"

shell> cat roles/test/tasks/main.yml
- debug:
var: people

Error: combine expects dictionaries
If you run the code on Ansible 2.9 or older you'll see the error

{"msg": "|combine expects dictionaries, got ({'var2': 'skywalker'},
{'name': 'TheSimpsons', 'var1': 'homer', 'var2': 'simpson'})"}

Fix the problem by mapping the tuples to the lists. This fix is upwards compatible.
people: "{{ people_defaults|product(people_vars)|map('list')|map('combine')|list }}"

Q: "Combination of the lists does not preserve the hierarchy of variables."
A: You're combining dictionaries. A dictionary(mapping) in YAML is an unordered set of key/value node pairs. See Mapping. The sorting is up to you. See Ansible list not ordered.}