I like a lot that for a simple change that may involve adding and / or editing files, I can just call `arc diff` and Arcanist will prompt to include or not each change. That allows to skip the `git commit` step.
However, if `arc land` fails due to a merge conflict and you call `git mergetool`, resolve it and call again `arc diff`, the fixed revision is correctly pushed to Differential, but it will fail again if you try to `arc land` it.
The solution is to call `git commit` before calling `arc land`.
For consistency the simple case described above, and also to avoid an extra step, it would be nice if `arc diff` could take care of calling `git commit` (it looks like there's already a commit message ready in there anyway), or at least prompt for it.