Apply Format in Place when Revisions Are Provided and End Revision is HEAD

[haohu321]

Is your feature request related to a problem? Please describe.
After the user commit changes, it will be impossible for him to apply the formatting using darker. A work around would be reset the commit and then recommit. Or try generate a diff patch and git apply (tried this but doesn't work).

Describe the solution you'd like
Ideally if the end revision is HEAD, we should still allow darker to apply the file changes. Then the user could easily
darker --revision=HEAD^..HEAD .

Describe alternatives you've considered

1. Git reset, run darker and then re-commit. This would be very tedious if the user has a long history of local commit unless the user squash, reset, run darker and then recommit.
2. Let darker generate a diff then try to apply as git patch. The output from darker can't be applied directly by git apply.

Additional context
Add any other context or screenshots about the feature request here.

[akaihola]

Thanks @haohu321 for the report!

Could you clarify what you mean by "impossible to apply formatting using Darker"?

Let's try to create a practical use case, maybe that will help me understand:

• git checkout main
• make some code modifications
• git add .
• git commit -m "Code modifications which don't comply with Black"
• darker -r main..HEAD
• git diff <- this should now show Darker's reformatting to the modified lines

At this point, you could either

• add reformatting as a separate commit: git add . ; git commit -m "Darker reformatting", or
• amend to the last commit: git commit --amend -m "Code modifications and Darker reformatting"

Could you point out which part of this workflow is failing for you?

[haohu321]

Hi @akaihola , thanks for taking a look. This is what's broken for me:

$ darker --revision=HEAD^..HEAD .
argument -r/--revision: Can't write reformatted files for revision 'HEAD'. Either --diff or --check must be used.

$ darker -r HEAD^..HEAD .
argument -r/--revision: Can't write reformatted files for revision 'HEAD'. Either --diff or --check must be used.

darker forces me to supply --diff or --check Is this a potential bug?

Also a minor issue: After pip install darker==2.1.1, darker --version always shows 1.2.1 I guess the version needs to be fixed

[akaihola]

@haohu321 this is intentional. It only makes sense to modify files on disk when comparing old revisions to the working tree (--revision=<old>..:WORKTREE:, shorthand --revision=<old>).

If you're comparing already committed revisions (--revision=<older>..<old>), and some lines were modified and not properly formatted between those revisions, it's not safe to reformat the files on disk in the working tree since there may have been later modifications either in commits after <old> or in the working tree.

So it's important to be aware that HEAD is different from :WORKTREE:.

I'd love to improve the documentation and/or error messages to make this clear – and feel free to challenge this design if you think it doesn't make sense!

Thanks for the --version bug report, it's actually a long-standing open issue (#593) and will be fixed in the next release.