{{ from_dttm }} and {{ to_dttm }} Jinja special variables are not rendered in Custom SQL metrics

[EBoisseauSierra]

When using Jinja special variables in Custom SQL metrics (Explore Panel), {{ from_dttm }} and {{ to_dttm }} are not rendered — unlike, say, {{ current_user_id() }}.

How to reproduce the bug

Turn Jinja templating feature flag on:

FEATURE_FLAGS ={
    "ENABLE_TEMPLATE_PROCESSING": True,
}

1. Go to your_dataset/BigNumber/Explore Panel
2. Click on Metric/Custom SQL
3. Use following definition:
   a. MIN({{ current_user_id() }})
   b. MIN('{{ from_dttm }}')

Expected results

Both definitions to return a number.

Actual results

• MIN({{ current_user_id() }}) returns a result:

by executing the following query

SELECT MIN(3) AS "MIN({{ current_user_id() }})"
FROM my.db
WHERE timestamp >= TO_TIMESTAMP('2022-03-01 00:00:00.000000', 'YYYY-MM-DD HH24:MI:SS.US')
  AND timestamp < TO_TIMESTAMP('2022-04-01 00:00:00.000000', 'YYYY-MM-DD HH24:MI:SS.US');

• But MIN('{{ from_dttm }}') returns “No Data” (even with a Time Range filter set).

executing this query:

SELECT MIN('{{ from_dttm }}') AS "MIN('{{ from_dttm }}')"
FROM my.db
WHERE timestamp >= TO_TIMESTAMP('2022-03-01 00:00:00.000000', 'YYYY-MM-DD HH24:MI:SS.US')
  AND timestamp < TO_TIMESTAMP('2022-04-01 00:00:00.000000', 'YYYY-MM-DD HH24:MI:SS.US');

Environment

(please complete the following information):

• superset version: 1.4.1 (and also on https://c96e35bc.us2a.app.preset.io/ on 2022-04-06)
• python version: 3.7.3
• any feature flags active:
  • ENABLE_TEMPLATE_PROCESSING

Checklist

Make sure to follow these steps before submitting your issue - thank you!

• I have checked the superset logs for python stacktraces and included it here as text if there are any.
• I have reproduced the issue with at least the latest released version of superset.
• I have checked the issue tracker for the same issue and I haven't found one similar.

Additional context

• Database engine: PostgreSQL
• The only valid syntax for {{ from_dttm }} is using single quotes (i.e. sum('{{ from_dttm }}')). Indeed, both {{ from_dttm }} (no quotes) or "{{ from_dttm }}" (double quotes) yield an error.