Fix issue #361 - add persistence for priority on completion, as an option defaulting to original behavior

[wwalker]

Before submitting a pull request, please make sure the following is done:

• Fork the repository and create your branch from master.
• If you've added code that should be tested, add tests!
• Ensure the test suite passes.
• Format your code with ShellCheck.
• Include a human-readable description of what the pull request is trying to accomplish.
• Steps for the reviewer(s) on how they can manually QA the changes.
• Have a fixes #XX reference to the issue that this pull request fixes.

Reviewer, manual QA of change:
Setup:

todo.sh add "(A) my task loses priority"
todo.sh add "(A) my task keeps priority"

Testing:
Verify no change in existing functionality:
Run:

@$ todo.sh do 1
1 x 2021-09-19 my task loses priority
TODO: 1 marked as done.

Verify that the Priority is removed, as is the currently expected behavior:

@$ todo.sh list
2 (A) my task keeps priority
1 x 2021-09-19 my task loses priority
--
TODO: 2 of 2 tasks shown

Verify that the new feature works (allow persistence of priority after completion, if user specifies -m):
Run:

@$ todo.sh -m do 2
2 x 2021-09-19 (A) my task keeps priority
TODO: 2 marked as done.

Verify that the Priority persists after the completion:

@$ todo.sh list
2 x 2021-09-19 (A) my task keeps priority
1 x 2021-09-19 my task loses priority
--
TODO: 2 of 2 tasks shown

[inkarkat]

You've just adapted the existing tests (and added manual QA steps in the PR text itself) - I'd like to have this covered (both command-line option and the config variable similar to TODOTXT_DATE_ON_ADD=1 in t1030-addto-date.sh) to prevent any regressions in that area.

The spec recommends to use metadata (i.e. turning (A) into pri:a) instead of keeping the priority as-is. Would that work for you, too?

[inkarkat]

I wonder whether this needs to be exposed as a command-line option - it struck me as noteworthy that most of your proposed change is about these boilerplate modifications, and the actual extension is just a few lines.

I guess most users would like to permanently configure TODOTXT_PRESERVE_PRIORITY=1 in the config file, anyway. (The same argument applies to the existing auto-archive, preserve line-numbers, and date prepending; unfortunately, these already have set the precedent in favor of short options, and it's getting increasingly more difficult to find good candidate letters.)

For my own scripts, I'd just offer a long GNU-style command-line option a la --keep-priority-on-done for this. But this would mean switching to GNU getopt (which is a separate dependency on Mac OS), and many adaptations. (And I wouldn't expect you to do this as part of this PR - this is just me brainstorming for the co-developer.)

[inkarkat]

I think the "maintain" is meant to establish a mnemonic for the chosen option letter, but it sounds a bit confusing to my non-native ears. I'd prefer Don't remove a priority on completion.

[wwalker]

Agreed, on both points.

[inkarkat]

Those purely cosmetic, I'd prefer to keep the variable $item inside the double quotes as "${item}s/^(.) //". My shellcheck isn't clever enough to figure out that the word-split variable contents can safely be kept outside quotes.

[chrysle]

@wwalker Is this still work in progress?