Recurrence based on the later of completion or due date (or have recurrent due date be a strictly later date)

[bleeben]

Making this idea after looking at #609 and #611, and trying out https://jakubroztocil.github.io/rrule/
I'd like to set up routine tasks that would be due (for example):

• every week on Monday
• every month on the 1st and 16th

Right now, if I try this without a 'when done' flag, then a heavily overdue task will require catching up (which I think is expected). And a current task without a 'when done' flag will also recur as expected.

However, if I try this with a 'when done' flag, it runs into something unexpected, where the next recurrence of the task will remain unchanged for a current task - replication below.

Expected Behavior

• Test 4 🔁 every month on the 1st and 16th when done ⏳ 2022-05-27 📅 2022-06-01
• Test 4 🔁 every month on the 1st and 16th when done ⏳ 2022-05-11 📅 2022-05-16 ✅ 2022-05-04

Current Behavior

• Test 4 🔁 every month on the 1st and 16th when done ⏳ 2022-05-11 📅 2022-05-16
• Test 4 🔁 every month on the 1st and 16th when done ⏳ 2022-05-11 📅 2022-05-16 ✅ 2022-05-04

Steps to Reproduce

• Test 4 🔁 every month on the 1st and 16th when done ⏳ 2022-05-11 📅 2022-05-16

On one hand, it's understandable for the recurrence to just pick up the next available date after 'when done' (so since 2022-05-16 is after 2022-05-04, it looks like that's what is used for the next recurrence due date. However, that makes the recurrence unusable until the due date is passed. I would request that either:

1. The next due date is calculated to be strictly after the previous due date (so that the current behavior is treated as a bug)
   or
2. There to be an option to set the recurrence (or otherwise dtstart) on the later of completion or current due date, which would also allow the next recurrence to progress forward.

[claremacrae]

I would expect that the code currently uses this to update dates relatively...
https://schemar.github.io/obsidian-tasks/getting-started/recurring-tasks/#priority-of-dates

Do you experiments confirm that?

[bleeben]

The relative dates are fine, actually - scheduled and start dates when present are correctly relative to the recurring due date - the issue is solely with the due date itself. From experimenting, all the behaviors are the same even if the scheduled and start dates are taken out.

[claremacrae]

Whilst it's fresh, please could you add a note in your reproduction steps to say what date you marked the task as done? This will be important in future for writing tests, when/if this request is picked up.

Never mind - it's in the text, as Done Date ...

[schemar]

Thank you for the well written idea, @bleeben! I think it makes sense. Please note that this does not have high priority at the moment, though.