add error for committing an empty file set without a message

[asibahi]

hit this a few times unintentionally doing AoC, where the warning shown is hidden by the new editor opening, doing something like jj commit d5p1.

I have not done items in the checklist below because I am not sure if this is even the best approach.

Edit: On a personal level I'd rather the file set become the message in this case but that's probably not something jj wants to do.

Checklist

If applicable:

• I have updated CHANGELOG.md
• I have updated the documentation (README.md, docs/, demos/)
• I have updated the config schema (cli/src/config-schema.json)
• I have added/updated tests to cover my changes

[github-actions]

The following commits do not follow our format for subject lines:

• 9f3916e: add error for committing an empty file set without a message

Commits should have a subject line following the format <topic>: <description>. Please review the commit guidelines for more information.

All commits are now correctly formatted. Thank you for your contribution!

[PhilipMetzger]

related issue #4414

[yuja]

I think it's valid to create an empty revision with an empty description. It might be okay to show a warning or a hint, though.

[asibahi]

I think it's valid to create an empty revision with an empty description. It might be okay to show a warning or a hint, though.

This still can be dome intentionally with -m "".

As is, the existing warning gets printed then immediately hidden by the editor window. Isaac mentioned on discord that the editor returning a non-0 exist code would abort the operation, (and it exists on vim and helix with :cq,) but that's not immediately obvious.

[yuja]

Since it's not wrong to create a commit with no description, -m '' shouldn't be required. That's the point. You can undo the commit if it was a mistake.

[asibahi]

what is the point of the commit command if there is no message, tho? then it is just new.

note that this PR is only about the situation where an empty file set is provided (which already has a warning) and no message provided, which I think is more likely to be a mistake than not.

[yuja]

Yes, it's just new (plus an empty describe, which isn't an error either.) I prefer not adding special error condition which isn't actually invalid.