referencing one commit in another for git

[Yuri Pankov]

Warner Losh wrote:
> On Wed, Dec 23, 2020 at 6:22 PM Jan Beich <jbeich at freebsd.org> wrote:
> 
>> Warner Losh <imp at bsdimp.com> writes:
>>
>>> On Wed, Dec 23, 2020, 3:21 PM Alan Somers <asomers at freebsd.org> wrote:
>>>
>>>> On Wed, Dec 23, 2020 at 3:16 PM Rick Macklem <rmacklem at uoguelph.ca>
>> wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> So I just did my first git commit. Pretty scary, but it looks ok.
>>>>>
>>>>> Now, how do I reference one commit in another related
>>>>> commit's log?
>>>>>
>>>>> By the long winded hash or ??
>>>>>
>>>>> I'm not sure if I should ask here or on the git mailing list,
>>>>> but I figured this isn't a technical git question...
>>>>>
>>>>> Thanks for any help with this, rick
>>>>>
>>>>
>>>> Yeah, you should use the full hash.  For temporary references, like
>> during
>>>> a code review, you can use the first "several" digits of the hash.
>>   For a
>>>> project of FreeBSD's size, "several" is probably 11-13.  But in
>> permanent
>>>> contexts, like commit logs, you should use the full hash.  When somebody
>>>> views the commit on a platform like Github, Github will automatically
>> turn
>>>> it into a hyperlink, and display only the first "several" digits.
>>>>
>>>
>>>
>>> For MFCs we are recommending the first 11. I think this will likely
>> suffice
>>> and matches the git client behavior.
>>
>> Mercurial defaults to 12 digit abbreviation. Git abbreviates linux,
>> freebsd-legacy, freebsd-ports repos on GitHub to 12 digit.
>>
> 
> I've updated to 12. That sounds like a good number of digits...Thanks.

I think the common way is to use `git rev-parse --short <fullhash>`, 
though we are likely to recommend increasing the core.abbrev value which 
sets the minimum length of unique prefix (default is 4).