From: lilinchao@oschina.cn <lilinchao@oschina.cn>
Date: Wed, 28 Jul 2021 04:45:21 GMT
Subject: Re: Re: git apply --3way behaves abnormally when the patch contains binary changes.
Message-ID: <9f510f56ef5e11eb90f70026b95c99cc@oschina.cn>
In-Reply-To: <4eb90a4eef4011ebab68d4ae5272fd1139378@pobox.com>

The defective test demo I provided is not that important(for me), the purpose of this is to
bring out our topic that "git apply -3" behaves differently on different Git version when
the patch is binary.
Maybe I would say this breaks backward compatibility, but the poor test demo didn't prove this. 
If anyone would like to see the incompatibility, he can run "git apply --index  -3 binary.diff" in command line in different Git version environment.

>Jerry Zhang <jerry@skydio.com> writes:
>
>>>         # 2. based on left_bin branch, make any change, and commit
>>>         git checkout -b right &&
>>>         cat bin.png bin.png > bin.png &&
>>>         git add bin.png &&
>>>         git commit -m "update binary file" &&
>>>
>>>         # 3. make patch
>>>         git diff --binary left..right >bin.diff &&
>>>         # apply --3way, and it will fail
>>>         test_must_fail git apply --index --3way bin.diff
>>> '
>>> "
>>>
>>> But  "git apply --index --3way bin.diff" will not faill on Git version 2.31.0.
>> Are you sure? I checked out to "commit
>> a5828ae6b52137b913b978e16cd2334482eb4c1f (HEAD, tag: v2.31.0)" and
>> rebuilt and ran your test snippet and it still failed.
>
>Isn't it just because the reproduction recipe is simply wrong?
>
>It says
>
>    * be on left branch and have a binary file
>    * be on right branch and have a modified binary file
>    * create a patch to take left to right
>
>Notice that we have a patch and we are still on the right branch.
>Of course, applying the patch to take us from left to right would
>fail from that state, but I _think_ the intent of the reproduction
>recipe was, after all of the above, do this here:
>
>    * switch to left branch and attempt to apply the patch.
>
>And the patch is meant to take us from left to right, and we are on
>pristine left, the application ought to cleanly succeed, no?
>
>"git apply bin.diff" would probably work correctly but I do not know
>offhand what the code after your change does with --3way enabled.
>
>We refuse to merge binary files, so I would not be surprised if we
>failed the 3way in this case (even though we _could_ fast-forward,
>it may not be worth complicating the --3way logic---nobody sane
>would say --3way when it is unnecessary) but after 3way fails, do we
>still correctly fall back to "straight application" like we do for
>text patches with your change?  Before your change, we would have
>first attempted the "straight application", which would succeed and
>wouldn't have hit "3way will refuse to merge binaries" at all.
>
>So, I do not think it is implausible that we are seeing a legit
>regression report.
>
>Thanks.