jj commands should throw a warning when the fileset does not exist

[whereistejas]

Closes #6556.

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:

• a98a670: Use print_unmatched_explicit_paths in cmd_status.
• 14e7bbd: Update CHANGELOG

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!

[martinvonz]

nit: Please squash this change into the parent commit.

I'm not sure we even need to mention it in the changelog. Users will notice the new warning when they run into it anyway. I can see some small value in having it there e.g. if a user is wondering why they're not seeing the warning when they're on an older version than their friend who is seeing the warning. Then they can check the changelog to see why. If we do add the changelog entry, it would be nice if it was just one entry for all remaining commands (see my other comment), so we don't end up with 10 different entries as we add the warning in new places.

[glehmann]

IMO, you should merge the revision that changes the command and the revision that adds the test for each command. It would be easier to review.
And it's a bit strange, given how the revisions are organized, that the number of revisions in the PR is odd :)

[whereistejas]

IMO, you should merge the revision that changes the command and the revision that adds the test for each command. It would be easier to review.

I want to make sure that the warning is shown in a consistent manner across all commands. That's why the commands and tests are one after another. I would be happy to split the PR in whatever way is more convenient for the reviewer when ready :)

And it's a bit strange, given how the revisions are organized, that the number of revisions in the PR is odd :)

I didn't have to add tests for all the commands. Some of them already had tests capturing this behaviour, for example, split.

[martinvonz]

nit: Could you squash the tests into the commit they're testing? See https://jj-vcs.github.io/jj/latest/contributing/#commit-guidelines