Re: [PATCH v3] [GSOC] ref-filter: fix read invalid union member bug

From: ZheNing Hu <adlternative@gmail.com>
Date: May 10, 2021, 12:51 UTC
Message-ID: <CAOLTT8R3ys5ohujVRKiQa3vijrzdGzLThU5hsG-estiyUgOqhQ@mail.gmail.com>
In-Reply-To: <xmqqcztzqc9j.fsf@gitster.g>

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> Just a final sanity check.  Is this a recent breakage or was the
> code introduced at cc72385f (for-each-ref: let upstream/push
> optionally report the remote name, 2017-10-05) broken from the
> beginning?
>

Well, The trigger condition is very special, but the bug was introduced at that time. Let's see the "bug" example below.

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> I am wondering if it is easy to add a test to cover the codepath
> that is affected by this change.
>
> Thanks.
>

Well, because this bug must require that the seventeenth bit of `used_atom.u` is not 0, it took me a long time to find this bug. in `used_atom.u`, only the member "color" and "contents" which size is bigger than 17 bytes, but "%(contents:trailer:only)" only fill the 16th byte of `used_atom.u`.

"Fortunately", I found it.

git for-each-ref --format='%(color:#aa22ac)'

I will add test for it!

Thanks! -- ZheNing Hu