twigfiddle.com - Fiddle 28bfqg v1 - Created on September 11, 2019 16:16

File
{% set sets = [
    {set: 'Set A', options: ['a1', 'a2', 'a3']},
    {set: 'Set B', options: ['b1', 'b2', 'b3']},
    {set: 'Set C', options: ['c1', 'c2', 'c3']},
    {set: 'Set D', options: ['d1', 'd2', 'd3']},
] %}

{# based on this: https://stackoverflow.com/a/29145116 #}

{# Combine with set name plus attribute #}

{% set combinations = [[]] %}
{% set combinationKeys = sets|keys %}

{% for key in combinationKeys %}
    {% set tmpCombinations = [] %}
    {% for v1 in combinations %}
        
        {% for v2 in sets[key].options %}
            {% set tmpCombinations = 
                tmpCombinations|merge(
                    [
                        v1
                        |merge([{ 'set': sets[key].set, 'option': v2 }])
                    ]
                ) %}
        {% endfor %}
    {% endfor %}
    {% set combinations = tmpCombinations %}
{% endfor %}

{# Combine with just attributes as an array #}

{{combinations|json_encode(constant('JSON_PRETTY_PRINT'))|raw}}

{% set combinations = [[]] %}
{% set combinationKeys = sets|keys %}

{% for key in combinationKeys %}
    {% set tmpCombinations = [] %}
    {% for v1 in combinations %}
        
        {% for v2 in sets[key].options %}
            {% set tmpCombinations = 
                tmpCombinations|merge(
                    [
                        v1
                        |merge([v2])
                    ]
                ) %}
        {% endfor %}
    {% endfor %}
    {% set combinations = tmpCombinations %}
{% endfor %}

{{combinations|json_encode(constant('JSON_PRETTY_PRINT'))|raw}}
Format