lib/time: consider any Time other than zero instant to be truthy

[SamWheating]

I know that the truthiness of timestamps isn't well defined, but the current behaviour is the opposite of what I would expect:

Welcome to Starlark (go.starlark.net)
>>> bool(time.now())
False
>>> bool(time.parse_time("0001-01-01T00:00:00Z"))
True

This change inverts the existing logic so that any time other than 0001-01-01T00:00:00Z will evaluate to True.

Alternatively, I think that considering all times to be True would also be acceptable. Thoughts?

[adonovan]

This was clearly just a mistake that no-one noticed until now. Thanks for the fix!

[SamWheating]

No problem, thanks for the quick review!

I'm pretty interested in this project - do you mind if I pick up a few of the TODOs? Got any new features or library modules you've been thinking about?

[adonovan]

I'm pretty interested in this project - do you mind if I pick up a few of the TODOs? Got any new features or library modules you've been thinking about?

Please do! I don't have any specific new features in mind. Much of the effort of this project has been spent in trying to harmonize the two (now three) implementations around a common spec, and to be very judicious about new features. Feel free to have a crack at any TODO comment in the code, and don't hesitate to ask for clarification before spending significant effort. These issues too might be suitable tasks, depending on your tastes:

#356
#249
#270
#271
#292

Many thanks for the kind offer.