Re: git-svn and huge data and modifying the git-svn-HEAD branch directly

On Wednesday 01 March 2006 20:11, Junio C Hamano wrote:

The latter at first sounds sane, but it has a subtle issue,
which was what bitten me previously between heads/ and tags/.
In that broken version, if you have a head called "dead" and a
tag with the same name, neither was taken ("they are not unique,
so do not take either!") and we ended up finding an object whose
SHA1 name began with those two bytes 0xDE 0xAD.  I do not think
this has happened in the field, fortunately, but it would have
been quite hard to diagnose.

So if we were to do it, I would say do the latter, but be very
careful to make sure you fail the whole get_sha1() when you bail
out of the "try possible prefixes" codepath because of
ambiguity.

Yes.
Any ambiguity is a source of confusion and user error. Better
bail out. If it is not a performance problem, it would be better
to integrate the check for abbreviated object name into the
ambiguity analysis, and not have 2 stages of searching.
It probably would be a good idea to print out the ambigous names
with the error message, so that you can copy&paste the correct
full name afterwards.

If we go for the .git/refs/remotes/... and have an ambiguity becaues
of remote shortcut names, a error message pointing at a "git-rename-remote"
command would be handy, allowing the user to cleanup the namespace.

There may be other issues involved, but I wouldn't 
know -- I reverted the "do not take either if they are
ambiguous between heads/ and tags/" patch primarily because of
the reason from the above paragraph, but also did not want to
deal with any other potential issues to keep my sanity ;-).

I think the real problem here is that names like "dead" can be interpreted
as abbreviated object name. When you introduce such a name as head or tag,
you have a potential ambiguity which can get real at any time.
Perhaps it would be good to print out a warning when the user is about to
create a head or tag name which can be interpreted as abbreviated object name?

Josef