Re: [PATCH] fetch: do not pass ref-prefixes for fetch by exact SHA1

From: Junio C Hamano <gitster@pobox.com>
Date: Jun 1, 2018, 02:12 UTC
Message-ID: <xmqqtvqn9rwa.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <20180531072339.GA43435@aiede.svl.corp.google.com>

Jonathan Nieder <jrnieder@gmail.com> writes:

Show 30 quoted lines

> When v2.18.0-rc0~10^2~1 (refspec: consolidate ref-prefix generation
> logic, 2018-05-16) factored out the ref-prefix generation code for
> reuse, it left out the 'if (!item->exact_sha1)' test in the original
> ref-prefix generation code. As a result, fetches by SHA-1 generate
> ref-prefixes as though the SHA-1 being fetched were an abbreviated ref
> name:
>
>  $ GIT_TRACE_PACKET=1 bin-wrappers/git -c protocol.version=2 \
> 	fetch origin 12039e008f9a4e3394f3f94f8ea897785cb09448
> [...]
>  packet:        fetch> ref-prefix 12039e008f9a4e3394f3f94f8ea897785cb09448
>  packet:        fetch> ref-prefix refs/12039e008f9a4e3394f3f94f8ea897785cb09448
>  packet:        fetch> ref-prefix refs/tags/12039e008f9a4e3394f3f94f8ea897785cb09448
>  packet:        fetch> ref-prefix refs/heads/12039e008f9a4e3394f3f94f8ea897785cb09448
>  packet:        fetch> ref-prefix refs/remotes/12039e008f9a4e3394f3f94f8ea897785cb09448
>  packet:        fetch> ref-prefix refs/remotes/12039e008f9a4e3394f3f94f8ea897785cb09448/HEAD
>  packet:        fetch> 0000
>
> If there is another ref name on the command line or the object being
> fetched is already available locally, then that's mostly harmless.
> But otherwise, we error out with
>
>  fatal: no matching remote head
>
> since the server did not send any refs we are interested in.  Filter
> out the exact_sha1 refspecs to avoid this.
>
> This patch adds a test to check this behavior that notices another
> behavior difference between protocol v0 and v2 in the process.  Add a
> NEEDSWORK comment to clear it up.

Thanks.

I wonder if there is a more effective way to smoke out other bugs remaining in proto v2. When the fetch-by-SHA1 feature was added originally, we certainly would have added a test or two to make sure it won't break. The root cause of this breakage is that we lack the ability to easily exercise proto v2 on these existing tests that were written back in the proto v0 days. It there were such a way (like, a common set of tests that are run with all supported protos), we would have caught the breakge even before the topic hit 'next'.