Re: git-cherry doesn't detect a "copied" commit

[Francis Moreau <francis.moro@gmail.com>]

On Fri, Oct 23, 2015 at 12:57 PM, Kevin Daudt <me@ikke.info> wrote:
> On Tue, Oct 20, 2015 at 06:32:12PM +0200, Francis Moreau wrote:
>> Hi,
>>
>> I'm seeing something odd with git-cherry: it doesn't seem to detect
>> that a commit has been cherry-picked from master branch.
>>
>> This happens with the systemd git repository (from github) so it
>> should be fairly simple to reproduce.
>>
>> What I did:
>>
>> $ git --version
>> git version 2.6.0
>> $ git checkout -b foo v210
>> $ git cherry-pick -x 9ea28c55a2488e6cd4a44ac5786f12b71ad5bc9f
>> $ git branch --contains 9ea28c55a2488e6cd4a44ac5786f12b71ad5bc9f
>> master
>> $ git cherry master HEAD
>> + fef60bf34d1b372bea1db2515a8d936386dfc523
>>
>> so git-cherry tells me that the cherry-picked commit has not
>> equivalent in master, which is no the case.
>>
>> What am I missing ?
>>
>
> Let's see:
>
>   $ git show | git patch-id
>   50c9f9548e1fd25401ff9540c82c1d5f9723c3d5 b4c86d2965aaf0736e4ab30be1d1a08931009a08
>
>   $ git show 9ea28c55a2488e6cd4a44ac5786f12b71ad5bc9f | git patch-id
>   a5cfbb542882bd9cbe192b43026354d1f2741673 9ea28c55a2488e6cd4a44ac5786f12b71ad5bc9f
>
> Git patch-id calculates the hash over the diff, and, when gives in this
> case two hashes, first the patch-id and the second the commit hash.
>
> The patch-ids are different, explaining why git cherry does not see them
> as equivalent. If I take a diff of the diff, I notice something:
>
>    diff --git a/src/udev/udevadm-settle.c b/src/udev/udevadm-settle.c
>   -index 927ea2a..65fc35f 100644
>   +index b026155..ea9b078 100644
>    --- a/src/udev/udevadm-settle.c
>    +++ b/src/udev/udevadm-settle.c
>    @@ -41,42 +41,28 @@
>   @@ -1094,7 +1094,7 @@
>                             exit(EXIT_SUCCESS);
>    @@ -102,44 +85,13 @@ static int adm_settle(struct udev *udev, int argc, char *argv[])
>                     default:
>   -                         assert_not_reached("Unknown argument");
>   +                         assert_not_reached("Unkown argument");
>                     }
>    +        }
>
> If you look at the lines with assert_not_reached, it seems there is a
> difference in the context of both diffs, causing the diffs to be
> different.
>
> Hope this helps, Kevin

Thanks Kevin

I was mislead by the git-cherry manpage somehow which says:

    "git-cherry therefore
     detects when commits have been "copied" by means of git-cherry-pick(1),

which is not exactly true.

Isn't there a way to get git-cherry less "strict" ?
I mean in this case most of 90% of the diff is the same, only one line
of context is not identical...

Would it make sense to add a "--fuzz" option which would reduce the
diff context area used to generate the hash ?

Thanks.
-- 
Francis