Re: [ANNOUNCE] Git v1.8.3-rc0

From: Junio C Hamano <gitster@pobox.com>
Date: Apr 28, 2013, 21:12 UTC
Message-ID: <7vvc76pdfc.fsf@alter.siamese.dyndns.org>
In-Reply-To: <517B62D8.5020006@alum.mit.edu>

Michael Haggerty <mhagger@alum.mit.edu> writes:

Show 26 quoted lines

> On 04/27/2013 04:24 AM, shawn wilson wrote:
>> On Fri, Apr 26, 2013 at 8:22 PM, Junio C Hamano <gitster@pobox.com> wrote:
>> 
>>>  * There was no good way to ask "I have a random string that came from
>>>    outside world. I want to turn it into a 40-hex object name while
>>>    making sure such an object exists".  A new peeling suffix ^{object}
>>>    can be used for that purpose, together with "rev-parse --verify".
>>>
>> 
>> What does this mean / what is the reason behind this? I can only think
>> it might be useful in a test suite to make sure git isn't doing
>> anything stupid with hashes...?
>
> The topic is discussed here:
>
> http://git.661346.n2.nabble.com/Bug-in-quot-git-rev-parse-verify-quot-td7580929.html
>
> As discussed in the thread, when verifying that an argument names an
> existing object, it is usually also appropriate to verify that the named
> object is of a particular type (or can be converted to a particular
> type), which could already be done with syntax like
> "$userstring^{commit}".  But if, for example, you want to avoid
> unwrapping tags but also want to verify that the named object really
> exists, "$userstring^{object}" now provides a way.
>
> And what do you have against test suites? :-)

And it is not about test in the first place. Git is designed to be scriptable, and it is not unreasonable for a scripted Porcelain to want to learn the full object name of the object that is referred to by a string that it suspects may be an object name. Perhaps you are feeding the entire git mailing list archive to a script that picks up any object name in the messages and tallying the number of times each object is mentioned. Then you would want to key the table that counts the number of appearances for each object with the object name, because different message may spell the name of the same object differently, e.g. f9fc12cf3, v1.8.3-rc0, etc. With a helper function "found_one_more_instance" that records the fact you saw another mention of an object, such a program may do something like this:

	tokenize_git_mailing_list_message |
        while read userstring
        do
		canonical=$(git rev-parse $userstring^{object}) &&
	        found_one_more_instance "$canonical"
	done