data.sls

settings:
  - foo
  - bar
  - baz: /opt

macro.jinja

{%- macro build_configure_options_from_settings(settings) -%}
  {%- set output = [] -%}

  {%- for item in settings['configure'] -%}
    {%- if item is mapping -%}
      {%- set output = output.extend(["--" + (item | join('='))]) -%}
    {%- else -%}
      {%- set output = output.extend(["--" + item]) -%}
    {%- endif -%}
  {%- endfor -%}


  {{ output | join(' ') }}
{%- endmacro -%}

output

Jinja variable 'None' has no attribute 'extend'
  [...]
  
    {%- for item in settings['configure'] -%}
      {%- if item is mapping -%}
        {%- set output = output.extend(["--" + (item | join('='))]) -%}
      {%- else -%}
        {%- set output = output.extend(["--" + item]) -%}    <======================
      {%- endif -%}
    {%- endfor -%}
  
  
    {{ output | join(' ') }}
  [...]