repo.index.diff("HEAD", create_patch=True) always empty

[jadinm]

I am using GitPython v2.1.11 with Python 3.6. My git version is 2.17.1.

I see inconsistent behavior of the diff method of a repo index if create_patch option set to True.
I am running the following script in a git repository with staged and unstaged changes.

from git import Repo

repo = Repo(".")

print(repo.index.diff("HEAD"))
print(repo.index.diff("HEAD", create_patch=True)) # Problem here

print(repo.index.diff(None))
print(repo.index.diff(None, create_patch=True))

But it prints:

[<git.diff.Diff object at 0x7fd54c328678>, <git.diff.Diff object at 0x7fd549e405e8>, <git.diff.Diff object at 0x7fd54c328558>]
[]
[<git.diff.Diff object at 0x7fd54c328678>]
[<git.diff.Diff object at 0x7fd54c328678>]

Somehow, the diff is empty if I set create_patch to True and the first argument to anything but None.
Do you know why it happens ?

[jadinm]

I found out the problem.

When running repo.index.diff("HEAD", create_patch=True), the command used is:

$ git diff -R <reference-hash> --cached --abbrev=40 --full-index -M -p --no-color

And this produces:

diff --git b/other_file.txt a/other_file.txt
deleted file mode 100644
index d733472942281cd2f19f52ab4b5ddecb4151bb72..0000000000000000000000000000000000000000
--- b/other_file.txt
+++ /dev/null
@@ -1 +0,0 @@
-Other file

But the regex that is used for parsing (i.e., Diff.re_header) expects a/other_file.txt to be before b/other_file.txt.
The inversion is due to the "-R" flag in the command line.

---

A temporary fix for my use of GitPython is to set R to True to prevent the reversal.

print(repo.index.diff("HEAD", create_patch=True, R=True))

[Byron]

Thanks a lot for sharing the issue, and for posting the workaround here as well!

[can-taslicukur]

I am using version 3.1.42 and experiencing this issue currently.

from git import Repo

repo = Repo(".")
print(repo.index.diff("HEAD"))
print(repo.index.diff("HEAD", create_patch=True))

print(repo.index.diff(None))
print(repo.index.diff(None, create_patch=True))

prints

[<git.diff.Diff object at 0x10cbb08b0>]
[]
[<git.diff.Diff object at 0x103d49d30>]
[]

R=True workaround does not help either:

print(repo.index.diff("HEAD", create_patch=True, R=True))
# []

This also happens when I try to diff tree against index or working tree

print(repo.head.commit.diff(None, create_patch=True))
print(repo.head.commit.diff(None))

print(repo.head.commit.diff())
print(repo.head.commit.diff(create_patch=True))

returns

[]
[<git.diff.Diff object at 0x103d69670>, <git.diff.Diff object at 0x103d699d0>]
[]
[<git.diff.Diff object at 0x103d69700>]

It looks like using create_patch=True when comparison includes index or working tree always returns empty list. So right now only way to reliably use create_patch=True is to diff tree against tree.