How to disable check for renames?

[dudicoco]

Hi,

I've tried to use the following to disable git diff renamed files search:

repo.index.diff('origin/HEAD', no_renames=True)

This did not work, and after some digging, i've found that GitPython hardcodes the -M flag:
https://github.com/gitpython-developers/GitPython/blob/master/git/diff.py#L106

Why is this flag hardcoded and is there a way around it?

Thanks

[Byron]

With this API there is no way around it unless the git command is used directly such as in repo.git.diff(…).
If there is motivation, a PR could be added to disable rename tracking which I presume is in the interest of increased performance.

[dudicoco]

@Byron there are two issues here:

1. Sometimes it is necessary to to add no-renames to prevent false positives in git's rename detection - for example, deleting a file and creating another file with similar content (this will be detected as rename, rather than delete + add).
2. It seems that there is a bug GitPython's diff filter when used with renames. To recreate, delete a file and create another file with similar contents, compare the result of git diff --name-only --diff-filter=M -M with GitPython's iter_change_type('M'). GitPython will show the deleted/renamed file as modified.

[mellowed100]

Hello! I've hit this issue as well. I'd like to try the repo.git.diff() approach as a workaround. Using the results from repo.git.diff(), is there an easy way to build a DiffIndex()?
Thanks!

[mellowed100]

        # remove -M arg if user supplies 'no_renames' or 'M' kwargs 
        if not any(x in kwargs for x in ('no_renames','M')):
            args.append("-M")  # check for renames, in both formats
        
        # manually convert '-M'
        if 'M' in kwargs:
            args.append(f"-M{str(kwargs['M'])}")
            del(kwargs['M'])
            

commitA.diff(commitB, M='75%')
produces:
git diff-tree 58259d006066372eb337cce81caf97365eb30f1e 22315b3c433865970e0a2fcd1b599786c2e01703 -r --abbrev=40 --full-index -M75% --raw -z --no-color

commitA.diff(commitB, no_renames=True)
produces:
git diff-tree --no-renames 58259d006066372eb337cce81caf97365eb30f1e 22315b3c433865970e0a2fcd1b599786c2e01703 -r --abbrev=40 --full-index --raw -z --no-color

default behavior stays the same
commitA.diff(commitB)
produces:
git diff-tree 58259d006066372eb337cce81caf97365eb30f1e 22315b3c433865970e0a2fcd1b599786c2e01703 -r --abbrev=40 --full-index -M --raw -z --no-color

[Byron]

Maybe that could be generalized (and tested) to become a contribution - it looks like a genuine improvement without adding too much complexity.

[mellowed100]

Hey Bryon,

So I took another look into the command line formatting issue. It turns out there is an option to format those single char kawrgs.
split_single_char_options controls the inclusion of a space character when constructing the git command line.

original:
commitA.diff(commitB, M='75%')

produces the -M 75%: (space included)
git diff-tree -M 75% 69a8e0b10c8695d7f073c3b32c647aa8e892b1e2 140ef4c33fa5a899cd8d1dfb15a03c342a49a95c -r --abbrev=40 --full-index --raw -z --no-color

Including option to format single char kwargs:
commitA.diff(commitB, split_single_char_options=False ,M='75%')
produces the -M75% (space removed)
git diff-tree -M75% 69a8e0b10c8695d7f073c3b32c647aa8e892b1e2 140ef4c33fa5a899cd8d1dfb15a03c342a49a95c -r --abbrev=40 --full-index --raw -z --no-color

So it looks like all we need is to remove the default -M when the user wants to override it with either --find-renames= or -M or --no-renames

    # remove default '-M' arg (check for renames) if user is overriding it
    if not any(x in kwargs for x in ('find_renames', 'no_renames','M')):
        args.append("-M")

The remaining kwargs can be processed through the normal routines.

[mellowed100]

It may also be worth adding the split_single_char_options option in the docs.

[Byron]

I see, thanks so much for investigating this. A PR to improve the situation would definitely be welcome. Thank you.

[nwcm]

would also like for this to be added!

[mellowed100]

Hey nwcm! The PR was finished last week. You can probably download the source now, or wait for the official 3.1.31 release.
#1551
Usage examples can be found in test/test_diff.py test_rename_override().