Dict to list

file.managed

# file.managed and cmd.run echo output
{"client": {"services": {"critical": "ReportServer$OLIVER,MSSQL$OLIVER,SoftlinkOliver"}}}

horrible.jinja

{%- set vars = salt['pillar.get']('sensu:vars', {}) -%}
{%- set vars_listified = {} -%}
{%- for service, values in vars.iteritems() -%}
  {# Create the service entry #}
  {%- do vars_listified.update({ service: {} }) -%}
  {%- if values is mapping -%}
    {%- for importance, items in values.items() -%}
      {%- set items_list = items.keys() | join(',') -%}
      {%- do vars_listified[service].update({ importance: items_list }) -%}
    {%- endfor -%}
  {%- else -%}
      {%- do vars_listified.update({ service: values }) -%}
  {%- endif -%}
{%- endfor -%}
{%- set client_vars = {} -%}
{%- do client_vars.update({ 'client': vars_listified }) -%}

pillar

sensu:
  vars:
    services:
      critical:
        # Use dict notation ('item':) instead :f list
        # notation (- 'item') for dict merging!
        'ReportServer$OLIVER':
        'MSSQL$OLIVER':
        'SoftlinkOliver':

rendered with file.serialize

...snip...
"vars": {
      "services": {
        "important": "u'salt-minion",
        "telegraf'": "None"
      }
    },
...snip...

template.yml

client:
  {# REQUIRED #}
  {% if salt['grains.get']('os_family') == 'Windows' %}
  name: {{ salt['grains.get']('host') | lower }}
  {% else %}
  name: {{ salt['grains.get']('localhost') | lower }}
  {% endif %}
  address: {{ salt['grains.get']('fqdn_ip4', [ 'localhost' ])[0] }}
  subscriptions: {{ salt['pillar.get']('nodegroups') }}

  {# KEEPALIVE #}
  keepalive:
    handlers:
      - default
      - saltstack

  {# CLIENT SOCKET #}
  socket:
    bind: 127.0.0.1
    port: 3030

  {%- set vars = salt['pillar.get']('sensu:vars', {}) -%}
  {%- set vars_listified = {} -%}
  {%- for service, values in vars.iteritems() -%}
    {# Create the service entry #}
    {%- do vars_listified.update({ service: {} }) -%}
    {%- if values is mapping -%}
      {%- for importance, items in values.items() -%}
        {%- set items_list = items.keys() | join(',') -%}
        {%- do vars_listified[service].update({ importance: items_list }) -%}
      {%- endfor -%}
    {%- else -%}
        {%- do vars_listified.update({ service: values }) -%}
    {%- endif -%}
  {%- endfor -%}
  {%- set client_vars = {} -%}
  {% do client_vars.update({ 'client': vars_listified }) %}

  vars: {{ vars_listified }}

  {# OPTIONAL #}
  domain: {{ salt['grains.get']('windowsdomain') }}
  os:
    family: {{ salt['grains.get']('os_family') }}
    name: {{ salt['grains.get']('osfullname') }}
  specs:
    cpu_model: {{ salt['grains.get']('cpu_model') }}
    cpu_num: {{ salt['grains.get']('num_cpus') }}
    mem: {{ salt['grains.get']('mem_total') }}

I realise this is ugly and hacky, but I needed a way to have values merged from different pillars, and empty dicts was the only way.

yeah, totally understand what you are trying to do.