Re: [RFC] git-pack-refs --prune

Linus Torvalds [off-list ref] writes:

The way to fix both these problems at once would be to add a flag to the 
"for_each_ref()", which says whether it followed a link, or whether it was 
already packed, so that we wouldn't pack symlinks at all, and we wouldn't 
add already-packed refs to the "keeprefs" list.

But that requires a sligh semantic extension to "do_for_each_ref()" (and 
"struct ref_list" needs a flag to say whether it was looked up through a 
symlink).

I was thinking that the easy way to solve it is to just _pack_ everything 
(the way we do now - incorrectly for symrefs), but never prune a symref.

I see.  Thanks for pointing out the issue with symrefs.  I think
clone with --use-separate-remote creates remote/$that_repo/HEAD
that points at the branch the remote side's HEAD points at (to
be precise, the one it guessed the remote side's HEAD points
at), so this is a real issue already.

I wanted to update for_each_ref() anyway for other reasons (it
really should take callback data -- the way the current users
use global variables to work this around is eyesore), so
hopefully I'll find time to take a look at it.

Rough outline:

 - for_each_ref() and friends become:

   typedef int each_ref_fn(const char *refname,
			   const unsigned char *sha1,
   #define REF_IS_SYMREF 01
   #define REF_IS_PACKED 02
                           int flags, /* above bits or'ed */ 
                           void *cb_data);
   int for_each_ref(each_ref_fn fn, void *cb_data);

 - handle_one_ref notices a symref and ignores it; it remembers
   refs that are not symref and are still loose for later
   pruning under --prune.

We might want to update the initial handshake of upload-pack
protocol so that peek-remote and fetch-pack can tell which one
is a symref pointing at what.  Do the usual server_capabilities
discovery in connect.c::get_remote_heads(), and if an extension
"symref" is supported than ask for symref information (typically
we would only get "HEAD points at refs/heads/foo" and nothing
else).  Then git-clone.sh does not have to make a guess.  But
that is a separate topic.