Fix panic in DateTime::checked_add_days

[Ekleog]

Incidentally, add TimeDelta::try_* builders so that it's possible to build them without risking a panic.

This issue was found thanks to cargo-bolero-fuzzing my web server, without actually trying to fuzz chrono itself.

[djc]

Going to close this. We'll review (and probably merge) #942 (the 0.4.x version of this change) and then eventually that change will make it to the main branch as part of a regular merge of 0.4.x work into main.

[Ekleog]

Hmm so I had opened both because this fix is IMO better than the one in #941 , as it can actually add some API surface to TimeDelta and doesn't need to rely on knowledge of Duration's internals. Now you're the one maintaining chrono so if the fix in #941 is good enough for you for 0.5 then as you wish, I just find it pretty ugly :)

[djc]

Ahh, sorry, had missed that context. Will open this back up, then we can review it after the other change has made its way into main.

[Ekleog]

Awesome thanks! :)

[djc]

(Merge is pending in #986.)

[djc]

Can you rebase this onto main? Should hopefully not be too painful.

[esheppa]

Looks good to me, pending rebase

[jtmoon79]

Can you add test cases for the before and after for all changed functions?
e.g. test_diff_days, test_weeks, test_try_weeks, etc.

Specifically, two commits

1. a commit with new test cases
2. a commit of these changes + adjustments to those test cases (if needed)

[Ekleog]

Sorry for the delay. I have basically not done any non-work software development for a few months, and have a few personal projects that will be higher priority for me than this PR, so I don't think I'll actually come back to this anytime soon.

Do you prefer if I leave the PR open so that someone else can easily notice it and take it over (and so that it tracks the fact that the panic is currently reachable on main), or should I just close it?

[pitdicker]

@Ekleog That is very reasonable. If it is ok with you I can take over in a couple of days.

[Ekleog]

That'd be perfect, thank you! :)

[pitdicker]

The new methods are included in #1137 together with other features for Duration. They are not yet merged however.