diff: geojson to console doesn't work for one dataset in a multi-dataset repo

[rcoup]

Describe the bug

Trying to get a geojson diff to stdout for working-copy changes to a single dataset. There are 3 vector datasets in the repository.

$ kart status
On branch main

Changes in working copy:
  (use "kart commit" to commit)
  (use "kart restore" to discard changes)

  road-centrelines-topo:
    feature:
      1 updates
$ kart diff -o geojson
Usage: kart_cli diff [OPTIONS] [COMMIT_SPEC] [FILTERS]...
Try 'kart_cli diff --help' for help.

Error: Invalid value for --output: Need to specify a directory via --output for GeoJSON with more than one dataset
$ kart diff -o geojson road-centrelines-topo
Error: road-centrelines-topo is not a ref, commit or tree
$ kart diff -o geojson road-centrelines-topo:
Error: road-centrelines-topo: is not a ref, commit or tree
$ kart diff -o geojson -- road-centrelines-topo
Error: road-centrelines-topo: is not a ref, commit or tree
$ kart diff -o geojson -- road-centrelines-topo:
Error: road-centrelines-topo: is not a ref, commit or tree

$ kart diff -o geojson --output .
$ ls
KART_README.txt  demo.gpkg  demo.gpkg-shm  demo.gpkg-wal  road-centrelines-topo.geojson

Expected behaviour

My changes are only to a single dataset, so there should be a way to return geojson from the diff without needing to write a file.

Version Info

• OS: macOS
• Version: v0.11.6.dev0

[rcoup]

Fix was bde1deb

Is there a way to limit the diff to a single dataset like you can with log?

[olsen232]

Yes, it even works nearly as you were doing above:
kart diff HEAD -o geojson road-centrelines-topo

The problem with kart diff and with kart show - and potentially other commands like commit - is that we don't understand -- properly. Click recognises it but hides it from us. Perhaps click applies some logic to it - maybe --aaa -- --bbb is parsed as option aaa and argument bbb.

@craigds fixed up kart log to understand --
It's not ideal in that it mostly bypasses click: it stops click from swallowing the --, and then we kind of get all the arguments in a big lump, instead of click sorting them out for us. It's then up to us to find the -- if present, and to separate them back into their argument types: commits and paths. But, perhaps we can't do much better: parsing the arguments in Git and now Kart is repository specific, since Git and now Kart checks to see if "road-centrelines-topo" is the name of a commit, or the name of a path. Anyway, I guess I need to pull that code out of log and figure out how to reuse it for diff, show, commit. I'll file a new bug.