Re: `ab | (cd cd && git apply -)' fails with v2.0.0

From: Michael J Gruber <git@drmicha.warpmail.net>
Date: Jul 25, 2014, 06:49 UTC
Message-ID: <53D1FDE2.8030309@drmicha.warpmail.net>
In-Reply-To: <xmqqegxaad3r.fsf@gitster.dls.corp.google.com>

Junio C Hamano venit, vidit, dixit 24.07.2014 19:19:

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> Michael J Gruber <git@drmicha.warpmail.net> writes:
> 
>> Steffen Nurpmeso venit, vidit, dixit 24.07.2014 15:29:
>>> Hello (again, psssssst, after a long time),
>>>
>>> it happened yesterday that i needed to do
>>>
>>>   $ git diff HEAD:FILE COMMIT:SAME-FILE |
>>>   > (cd src && git apply -) 
>>> ...
>>
>> Ah little more context would help. Are you diffing files in the subdir
>> src, or a file at the root which happens to be present in the subdir src
>> as well?
> 
> As the <treeish>:<path> form is not meant to produce "git apply"
> applicable patch in the first place, I am not sure what the OP is
> trying to achieve in the first place.  Not just "how many leading
> levels to strip?" but "which file is being modified?" does not
> appear in a usable form.  For example, here is what you would see:
> 
>     $ git diff HEAD:GIT-VERSION-GEN maint:GIT-VERSION-GEN
>     diff --git a/HEAD:GIT-VERSION-GEN b/maint:GIT-VERSION-GEN
>     index 40adbf7..0d1a86c 100755
>     --- a/HEAD:GIT-VERSION-GEN
>     +++ b/maint:GIT-VERSION-GEN
>     @@ -1,7 +1,7 @@
>     ...
> 
> and neither "HEAD:GIT-VERSION-GEN" nor "maint:GIT-VERSION-GEN" is
> the file being modified ("GIT-VERSION-GEN" is).

I thought "git apply" knows how to strip the rev part.

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> I would understand if the upstream of the pipe were
> 
>     $ git diff HEAD maint -- GIT-VERSION-GEN | ...
> 
> though.
> 
> Needless to say, if the place "cd" goes is not a worktree controlled
> by git, then "git apply" would not know where the top-level of the
> target tree is, so even though the input with the corrected command
> on the upstream side of the pipe tells it which file is being
> modified, it needs to be told with the proper -p<n> parameter how
> many leading levels to strip.

I think it's a common mistake to think of "git apply" as some sort of magic extension of "patch" which can do anything that "patch" does and more, and can be fed anything that "git diff" produces", figuring out by itself what to do with it :)

Michael