Metabase importer should preserve optional SQL clause filter behavior

[arsalann]

Summary

When importing Metabase dashboards, DAC currently strips Metabase optional SQL clause markers ([[ ... ]]) and emits warnings like:

Metabase optional SQL clause markers [[...]] were removed; review empty-filter behavior

This makes the imported dashboard structurally valid, but it can change widget behavior when a filter is empty. In Metabase, optional clauses are included only when their referenced variables have values. After import, the converted SQL may either always apply a clause or lose the intended conditional behavior, depending on how the marker is removed.

Why this matters

For production dashboard migration, this is one of the main manual-review risks after dac import metabase. A dashboard can validate successfully while still producing different results from Metabase for empty/default filter states.

Desired behavior

The Metabase importer should preserve optional clause semantics in DAC output, ideally by converting Metabase optional SQL blocks to equivalent DAC/Jinja conditionals.

For example, a Metabase query like:

SELECT *
FROM orders
WHERE 1 = 1
[[AND created_at >= {{start_date}}]]
[[AND customer_id = {{customer_id}}]]

could become something like:

SELECT *
FROM orders
WHERE 1 = 1
{% if filters.start_date %}
  AND created_at >= '{{ filters.start_date }}'
{% endif %}
{% if filters.customer_id %}
  AND customer_id = '{{ filters.customer_id }}'
{% endif %}

The exact output shape can follow DAC's preferred filter conventions, but the key requirement is that empty filter values do not alter the query compared with Metabase.

Suggested scope

• Detect Metabase optional SQL blocks during import.
• Preserve the optional behavior as DAC/Jinja conditionals when the referenced variable maps to a dashboard filter.
• If conversion is ambiguous, add a clear inline TODO/comment near the affected SQL rather than silently flattening the clause.
• Consider a stricter import option that fails when optional clause semantics cannot be represented safely.
• Include regression tests covering empty filter values, populated filter values, and multiple optional clauses in one query.

Current workaround

Manually review every warning from dac import metabase, inspect each affected widget, and rewrite the SQL conditionals by hand.