Subject: Re: [PATCH 2/4] glossary: define committish (a.k.a. commit-ish)

From: Richard Hansen <[email-masked]>
Date: Wed, 19 Jun 2013 18:23:51 -0400

On 2013-06-19 17:05, Junio C Hamano wrote:
> Richard Hansen <[email-masked]> writes:
> 
>> On 2013-06-19 13:14, Junio C Hamano wrote:
>>> <object-type>-ish does not have anything to do with a ref.  Even
>>> when an object is dangling in your object store without being
>>> reachable from any of your refs, it keeps its own "ish"-ness.
>>
>> Ah, so your personal definition of "ref" matches my personal definition
>> of "ref", and this definition doesn't match gitglossary(7).  :)
> 
> Huh?  The only thing I I said was that "*-ish" does not have
> anything to do with a ref.  I didn't say anything about definition
> of "ref".

The phrase

    when an object is dangling in your object store without being
    reachable from any of your refs

implies something about your definition of a ref that is inconsistent
with gitglossary(7).  See below.

> 
> You are the one who brought "ref" into description of *-ish, with
> this:
> 
>> +[[def_committish]]committish (also commit-ish)::
>> +	A <<def_ref,ref>> pointing to an <<def_object,object>> that
>> +	can be recursively dereferenced to a

And I did that to be consistent with the definition of tree-ish, which
currently says:

    tree-ish
        A ref pointing to either a commit object, a tree object, or a
        tag object pointing to a tag or commit or tree object.

Notice the term "ref" in the above definition.  This definition says
that a tree-ish is a particular kind of ref -- NOT a property of an
object as you claim.  I'm not saying you're wrong -- I actually agree
with you completely -- I'm just saying that your definition of ref
doesn't match the definition of ref in gitglossary(7).

The current definition of ref says:

    ref
        A 40-byte hex representation of a SHA-1 or a name that denotes
        a particular object.  They may be stored in a file under
        $GIT_DIR/refs/ directory, or in the $GIT_DIR/packed-refs file.

Depending on how one interprets "name" (which is not defined in
gitglossary(7)) in the above definition of ref, claiming that
"master:README" is a ref is consistent with gitglossary(7).  It is NOT,
however, consistent with what you -- or anyone else I know -- think of
as a ref.

> 
> All I am saying is that an object does not have to be pointed by any
> ref to be any-ish.  ish-ness is an attribute of an object, not an
> ref.  You do not say refs/heads/master (which is a ref) is a
> commit-ish or a tree-ish.  The object pointed at by that ref is
> always a commit and is a commit-ish and a tree-ish.

I understand and agree completely and always have.

Here's what I'm trying to say:

  * Given the current definition of "ref" in gitglossary(7), claiming
    that a foo-ish is a ref is not entirely incorrect.
  * If the definition of "ref" is altered to match the general
    understanding of a "ref", then claiming that a foo-ish is a ref is
    wrong.  Very wrong.

I was trying to be minimal and consistent with my changes, but
unfortunately it seems like more changes are necessary.  When I next
have time, I'll send some revised patches to include the following changes:

  * replace the current definition of "ref" with something that matches
    general understanding
  * eliminate the use of "ref" in the definitions of tag object, tree
    object, and tree-ish
  * create a term that means "a thing understood by rev-parse that
    uniquely identifies an object" (perhaps "object specifier"?) that
    can be used in gitglossary(7) and elsewhere

-Richard