Re: [PATCH v3] diff: make diff_free_filespec_data accept NULL

From: Jinoh Kang <luke1337@theori.io>
Date: Nov 10, 2020, 13:16 UTC
Message-ID: <17491ac3-ce1b-ca5d-d4e8-9fa8ab72d7e3@theori.io>
In-Reply-To: <nycvar.QRO.7.76.6.2011101257540.18437@tvgsbejvaqbjf.bet>

On 11/10/20 12:08 PM, Johannes Schindelin wrote:

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> Hi Jinoh,
> 
> On Fri, 6 Nov 2020, Jinoh Kang wrote:
> 
>> Commit 3aef54e8b8 ("diff: munmap() file contents before running external
>> diff") introduced calls to diff_free_filespec_data in
>> run_external_diff, which may pass NULL pointers.
> 
> Sorry for the breakage!

No worries. Those functions were indeed confusing...

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> 
> Maybe the commit message could talk a bit about the circumstances when
> this happens? Of course, I (and every other reader...) could analyze your
> patch to guess what it is that triggers the bug, but it's really a good
> use of the commit message to describe it in plain English.

Agreed. The v1 PATCH, which was off-list, did explain that NULL filespecs are used to indicate unmerged files (i.e. with unresolved conflicts).

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> 
>>
>> Fix this and prevent any such bugs in the future by making
>> `diff_free_filespec_data(NULL)` a no-op.
>>
>> Fixes: 3aef54e8b8 ("diff: munmap() file contents before running external diff")
> 
> I am unaware of any other commit having a `Fixes:` trailer in the commit
> message. In any case, I would have expected `Fixes:` to mention a ticket
> or a bug report, not the commit that fixed _a separate_ issue (but
> unfortunately introduced this regression).

Sorry for this one; somehow I didn't notice that git and linux use different conventions.

-- 
Jinoh Kang
Theori