Re: The case for two trees in a commit ("How to make rebase less modal")

From: Junio C Hamano <gitster@pobox.com>
Date: Mar 1, 2018, 18:44 UTC
Message-ID: <xmqqh8pzhbz3.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <CAGZ79ka6PXgs+JDicaQYWYSKgEthj0A-2bBaRcdp_0T2H+sREA@mail.gmail.com>

Stefan Beller <sbeller@google.com> writes:

Show 14 quoted lines

> $ git hash-object --stdin -w -t commit <<EOF
> tree c70b4a33a0089f15eb3b38092832388d75293e86
> parent 105d5b91138ced892765a84e771a061ede8d63b8
> author Stefan Beller <sbeller@google.com> 1519859216 -0800
> committer Stefan Beller <sbeller@google.com> 1519859216 -0800
> tree 5495266479afc9a4bd9560e9feac465ed43fa63a
> test commit
> EOF
> 19abfc3bf1c5d782045acf23abdf7eed81e16669
> $ git fsck |grep 19abfc3bf1c5d782045acf23abdf7eed81e16669
> $
>
> So it is technically possible to create a commit with two tree entries
> and fsck is not complaining.

The second one is merely a random unauthorized header that is not interpreted in any way by Git. It is merely being confusing by starting with "tree " and having 40-hex after it, but the 40-hex does not get interpreted as an object name, and does not participate in reachability computation (i.e. packing, pruning and fsck).

There is not much difference between that and a line of trailer in the commit log message (other than this one is less discoverable).