bug: ibis.now() has the wrong dtype on BigQuery backend

[ajmarks]

What happened?

ibis.now() is typed as a Timestamp without timezone, but the BigQuery backend renders it as CURRENT_TIMESTAMP(), which as its name indicates, returns a BigQuery TIMESTAMP (datetime with timezone) value.

Instead, it should render as CURRENT_DATETIME().

What version of ibis are you using?

10.7.0

What backend(s) are you using, if any?

BigQuery

Relevant log output

>>> bq_backend.execute(ibis.now().cast("string"))
'2025-11-19 20:47:00.004082+00'
>>> duck_db_backend.execute(ibis.now().cast("string"))
'2025-11-19 20:53:00.07'

Code of Conduct

• I agree to follow this project's Code of Conduct

[cpcloud]

I suspect this will break a lot of code if we change it, and we should look to see whether there's any existing consistency in ibis.now() timezone-y-ness across backends.

If we're going to break this, we should go for maximum consistency in this API.

[ajmarks]

That's fair. The problem right now is that this breaks backend independence. The workaround is also not great because TimestampNow is typed as dtype = dt.timestamp (link), so even explicit casts to "timestamp". Rather, one needs to do a cast to "timestamp('UTC')" (which is a NOP in BigQuery, but may not be in other backends) and then cast back plain "timestamp" to get ibis.now() as a (BigQuery) DATETIME:

>>> ibis.now()
TimestampNow(): TimestampNow()
>>> ibis.now().cast("timestamp")
TimestampNow(): TimestampNow()
>>> ibis.now().cast("timestamp('UTC')").cast("timestamp")
Cast(Cast(TimestampNow(), timestamp('UTC')), timestamp): Cast(Cast(TimestampNow(), to=timestamp('UTC')), to=timestamp)