On Sun, Jul 14, 2013 at 08:45:37PM -0700, Junio C Hamano wrote:

> >> To cat-file we could add an option like "--sha1-only" or "--literal" or
> >> "--no-dwim" (... better names are failing me) which would skip *all*
> >> dwimming of 40-character strings.  It would also assume that any shorter
> >> strings are abbreviated SHA-1s and fail if they are not.  This would be
> >> a nice feature by itself ("these are object names, dammit, and don't try
> >> to tell me differently!") and would have the additional small advantage
> >> of speeding up lookups of abbreviated SHA-1s, which (regardless of your
> >> patch) otherwise go through the whole DWIM process.
> >
> > I can see in theory that somebody might want that, but I am having a
> > hard time thinking of a practical use.
> Would it be a good alternative to call get_sha1_hex() to catch the
> most common case (reading from rev-list output, for example) and
> then let the more general get_sha1() to let extended SHA-1 to be
> handled?

For a 40-byte sha1, that _should_ be what get_sha1 does (i.e., go more
or less directly to the 40-hex code path, and return). And that's
basically what happens now, except that after we do so, we now have the
extra "oh, is it also a refname?" check.

For a shortened sha1, I don't think it would have the same behavior.
Right now, I believe the order is to treat a short sha1 as a possible
refname, and only if that fails consider it as a short sha1.

> > IOW, it seems like a poor default, and we are choosing it only because
> > of backwards compatibility. I guess another option is to switch the
> > default with the usual deprecation dance.
> I agree that "did you mean the unreadable refname or 40-hex object?"
> turned on everywhere get_sha1() is called is a very poor default.  I
> wonder if we can limit it only to the end-user input somehow at the
> API level.

It is easy to do on top of my patch (just flip the default on the switch
I introduced, and turn it back on in whichever code paths are
appropriate).  But the question is: what is end-user input? Do you mean
command-line arguments to "rev-list" and friends?

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