Markup timezone-aware time mentions

[preetmishra]

This adds support for rendering timezone-aware time mentions which were recently added to the Zulip's markdown suite.

(See https://zulipchat.com/help/format-your-message-using-markdown#mention-a-time for markdown details.)

Complimentary additions

• msg_time style in themes.py.
• TIME_MENTION_MARKER symbol in symbols.py.

Test amended.

Fixes #691.

[preetmishra]

It turns out the first-party datetime module doesn't have good support for handling ISO format strings for python < 3.7. This is where the module python-dateutil comes in with a parser.

The python-dateutil package also has tzlocal() for working with local time zones. However, it has a few caveats and is too tricky to mock and test. This is where the module tzlocal kicks in.

[neiljp]

@preetmishra Thanks for working on this - while entering the dates could be tricky in ZT (as discussed on czo), this will be useful to coordinate sync meetings for the rest of this Summer or generally across multiple timezones :)

I did notice that when I edit a date in ZT (possibly when I enter it wrongly first) then it doesn't update on the webapp, but I'm guessing that's an issue with the webapp - we re-fetch the message content and re-render fine from what I can tell.

This isn't a change in behavior, but perhaps we could indicate this is feature level 8/16 and new in v3.0?

[neiljp]

This may be clearer to some degree, but I quite like the stopwatch type icon, perhaps from having something similar for 'busy' icons in older systems! We could perhaps discuss this in the stream; these all seem like options:
⌚ U+0231A WATCH
⌛ U+0231B HOURGLASS
⏰ U+023F0 ALARM CLOCK
⏱ U+023F1 STOPWATCH
⏳ U+023F3 HOURGLASS WITH FLOWING SAND
⧖ U+029D6 WHITE HOURGLASS
⧗ U+029D7 BLACK HOURGLASS

[preetmishra]

Out of these, only ⏱, ⧖ and ⧗ seem to not cause the UI distortion bug that we have noticed in urwid.

However, the emoji ⏱ appears to consume an extra space character. To recoup, I have added an extra space in TIME_MENTION_MARKER itself, i.e., TIME_MENTION_MARKER = '⏱ '.

[neiljp]

This looks good for this v1 as per discussion in the stream 👍

[preetmishra]

@neiljp Thanks for the review. I couldn't reproduce the issue that you mentioned with the web app. It worked well for me.

The latest update only has the in-line suggestions incorporated and an extra comment about feature level and server version support.

[neiljp]

@preetmishra This looks good now, just pending:

• fix conflicts after the recent requirements merge
• maybe assert on input?
• symbol discussion on czo

I introduced some of the time mention ideas/issues in #general>Time mentions.

[preetmishra]

@neiljp Thanks for the review. I have made the suggested amendments in the latest update.

[sumanthvrao]

@preetmishra This looks great.

I happened to be on WSL when testing this and observed that the stopwatch icon appears much smaller than the other text. Small enough to be mistaken for a point, almost! Is this the same size in other platforms as well?

[preetmishra]

@sumanthvrao Thanks for the review. That looks strange. It renders well on my Ubuntu 20.04. Could you test with ⧗?

[neiljp]

@preetmishra Thanks! Merged with an adjustment to the commit text to indicate the server version/feature-level for time mentions 🎉