git-diff passes <rev>:<path> args to GIT_EXTERNAL_DIFF incorrectly?

From: Dmitry Nikulin <pastafariant@gmail.com>
Date: Aug 27, 2019, 18:24 UTC
Message-ID: <CAH53SykX12SN83=gey8KS_x3cGkXH758sfEieskXnnvos8DMcA@mail.gmail.com>

I wrote a very simple Python script to see which arguments git-diff passes to the external diff program when comparing files across branches:

$ env GIT_EXTERNAL_DIFF=./print_argv.py git diff
origin/branch1:file1.txt origin/branch2:file2.txt
['./print_argv.py',
 'file1.txt',
 '/tmp/QRaIJ1_file1.txt',
 '802b1c4ed7b06162b2ce09b7db72a576695b96e5',
 '100644',
 '/tmp/AZuOJ1_file2.txt',
 '076e8e37a712d8a66c0c3d1a103050dc509ca6ff',
 '100644',
 'file2.txt',
 'index 802b1c4..076e8e3 100644\n']

According to the docs (https://www.git-scm.com/docs/git/2.22.0#Documentation/git.txt-codeGITEXTERNALDIFFcode), git-diff is supposed to pass 7 parameters:

path old-file old-hex old-mode new-file new-hex new-mode

This is not what I am seeing here. Is this a bug or incorrect/incomplete documentation?

Tested with git 2.22.0 and 2.17.1.