Re: [PATCH] abbrev: allow extending beyond 20 chars to disambiguate

From: Junio C Hamano <gitster@pobox.com>
Date: Aug 11, 2025, 21:28 UTC
Message-ID: <xmqqzfc5zgxt.fsf@gitster.g>
In-Reply-To: <xmqq4iud1rfm.fsf@gitster.g>

Junio C Hamano <gitster@pobox.com> writes:

Show 11 quoted lines

> "brian m. carlson" <sandals@crustytoothpaste.net> writes:
>
>> On 2025-08-11 at 15:26:32, Junio C Hamano wrote:
>>> When you have two or more objects with object names that share more
>>> than half the length of the hash algorithm in use (e.g. 10 bytes for
>>> SHA-1 that produces 20-byte/160-bit hash), find_unique_abbrev()
>>> fails to show disambiguation.
>>
>> Is this really the case?  
>
> What I wrote in the above is correct.

Sorry, I meant "incorrect". And using GIT_MAX_HEXSZ will break the abbreviation system rather badly. It has to be the length of the hash that is being used.

Show 11 quoted lines

>
>> If the restriction is due to using
>> GIT_MAX_RAWSZ instead of GIT_MAX_HEXSZ, then that's 32 vs. 64 in our
>> modern codebase.
>
> The above numbers are correct but irrelevant ;-).
>
> The thing is, the offending commit changed from 40-bytes
> (GIT_SHA1_HEXSZ) to 32-bytes (GIT_MAX_RAWSZ).  Plase see v2 patch.
>
> Thanks.