Re: pushing for a new hash, was Re: [PATCH 2/3] rebase: Add tests for console output

From: Junio C Hamano <gitster@pobox.com>
Date: Jun 3, 2017, 00:36 UTC
Message-ID: <xmqqr2z1x5zh.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20170602175455.GA30988@aiede.mtv.corp.google.com>

Jonathan Nieder <jrnieder@gmail.com> writes:

Show 8 quoted lines

> 2. Hard-coded object ids in tests: As Stefan hinted, many tests beyond
>    t00* make assumptions about the exact values of object ids.  That's
>    bad for maintainability for other reasons beyond the hash function
>    transition, too.
>
>    It should be possible to suss them out by patching git's sha1
>    routine to use the ones-complement of sha1 (~sha1) instead and
>    seeing which tests fail.

One particularly nasty one is t1512-rev-parse-disambiguation that ensures that the abbreviation and disambiguation works correctly. It uses a set of objects (tags, commits, trees and blobs) whose object names all begin with number of "0"; which will of course become useless once we change the hash function.

No matter what new hash function is chosen, we'd need a similar test to ensure that disambiguation works correctly, so one of the tasks for hash migration is to port (not drop) this test.