[carljm]

Time objects may carry a timezone, and typeshed currently doesn't model the distinction between a timezone-aware vs timezone-naive time.

If a date is combined with a timezone-aware time using datetime.combine, the resulting datetime will have the same timezone. So it is incorrect for the overloads for datetime.combine to claim that combining a date and a time (with no explicit timezone in the combine call) necessarily returns a naive datetime.

We choose datetime[tzinfo] | datetime[None] because invariance of datetime makes this a more flexible type, compared to datetime[tzinfo | None]. This parallels the existing annotation of datetime.fromisoformat().

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

core (https://github.com/home-assistant/core)
+ homeassistant/components/hassio/auto_update.py:62: error: Need type annotation for "length"  [var-annotated]