gitconfig: mnemonicPrefix conflict with create_patch

the regex:

Line 372 in 6d09bb6

[ ](?P<a_path_fallback>"?[ab]/.+?"?)[ ](?P<b_path_fallback>"?[ab]/.+?"?)\n

is not able to match the diff generated if this flag is enabled in ~/.gitconfig:

[diff]
        mnemonicPrefix = true

because it is expecting [ab]/ as folder prefix for the diff but with mnemonicPrefix enabled it become [wc]/

Diff without `mnemonicPrefix`

diff --git a/.vscode/launch.json b/.vscode/launch.json
index xxxxxxx..xxxxxxxx
--- a/.vscode/launch.json
+++ b/.vscode/launch.json

Diff with `mnemonicPrefix = true`

diff --git c/.vscode/launch.json w/.vscode/launch.json
index xxxxxxx..xxxxxxxx
--- c/.vscode/launch.json
+++ w/.vscode/launch.json

Quick Test

repo = git.Repo('.')
branch_ref = repo.head
ancestor_ref = repo.merge_base(branch_ref, repo.refs["main"])
diff = ancestor_ref[0].diff(None, create_patch=True)
print(diff)

Thanks a lot for reporting!

To fix this, GitPython should control for this flag and turn it off when invoking Git, i.e. with git -c mnemonicPrefix=false.

@Byron

thanks @Byron, is it there a workaround I can use in the meantime?
something like:

diff = ancestor_ref[0].diff(None, create_patch=True, c='diff.mnemonicPrefix=false')

So far a quick workaround is:

diff = ancestor_ref[0].diff(None, create_patch=True, **{'src-prefix':'a/','dst-prefix':'b/'})

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gitconfig: mnemonicPrefix conflict with create_patch #2013

Diff without `mnemonicPrefix`

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gitconfig: mnemonicPrefix conflict with create_patch #2013

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Diff without mnemonicPrefix

Diff with mnemonicPrefix = true

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Byron commented on Mar 12, 2025

ceccopierangiolieugenio commented on Mar 13, 2025

ceccopierangiolieugenio commented on Mar 13, 2025

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Diff without `mnemonicPrefix`

Diff with `mnemonicPrefix = true`