Re: [PATCH v5 3/3] clone: respect remote unborn HEAD

[Jonathan Tan <jonathantanmy@google.com>]

> Jonathan Tan <jonathantanmy@google.com> writes:
> 
> >  init.defaultBranch::
> >  	Allows overriding the default branch name e.g. when initializing
> > -	a new repository or when cloning an empty repository.
> > +	a new repository.
> 
> Looking good.
> 
> > diff --git a/builtin/clone.c b/builtin/clone.c
> > index 211d4f54b0..77fdc61f4d 100644
> > --- a/builtin/clone.c
> > +++ b/builtin/clone.c
> > @@ -1330,10 +1330,21 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
> >  		remote_head = NULL;
> >  		option_no_checkout = 1;
> >  		if (!option_bare) {
> > -			const char *branch = git_default_branch_name();
> > -			char *ref = xstrfmt("refs/heads/%s", branch);
> > +			const char *branch;
> > +			char *ref;
> > +
> > +			if (transport_ls_refs_options.unborn_head_target &&
> > +			    skip_prefix(transport_ls_refs_options.unborn_head_target,
> > +					"refs/heads/", &branch)) {
> > +				ref = transport_ls_refs_options.unborn_head_target;
> > +				transport_ls_refs_options.unborn_head_target = NULL;
> > +			} else {
> > +				branch = git_default_branch_name();
> > +				ref = xstrfmt("refs/heads/%s", branch);
> > +			}
> >  
> >  			install_branch_config(0, branch, remote_name, ref);
> > +			create_symref("HEAD", ref, "");
> >  			free(ref);
> 
> OK, we used to say "point our HEAD always to the local default
> name", and the code is still there in the else clause.  But when the
> transport found what name the other side uses, we use that name
> instead.
> 
> I presume that clearing transport_ls_ref_options.unborn_head_target
> is to take ownership of this piece of memory ourselves?

Yes - just to be consistent with the other branch where "ref" needs to
be freed.

> We didn't call create_symref() in the original code, but now we do.
> Is this a valid bugfix even if we did not have this "learn remote
> symref even for unborn HEAD" feature?  Or is the original codepath
> now somehow got broken with an extra create_symref() that we used
> not to do, but now we do?

Ah...now I think I see what you and Peff [1] were saying. Yes I think
the symref creation is not necessary when we use the default branch name
(like we currently do). I'll verify and write back with my findings in
the next version.

[1] https://lore.kernel.org/git/YBCf8SI3fK+rDyox@coredump.intra.peff.net/

> 
> > @@ -1385,5 +1396,6 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
> >  	junk_mode = JUNK_LEAVE_ALL;
> >  
> >  	strvec_clear(&transport_ls_refs_options.ref_prefixes);
> > +	free(transport_ls_refs_options.unborn_head_target);
> >  	return err;
> >  }
> > diff --git a/connect.c b/connect.c
> > index 328c279250..879669df93 100644
> > --- a/connect.c
> > +++ b/connect.c
> > @@ -376,7 +376,8 @@ struct ref **get_remote_heads(struct packet_reader *reader,
> >  }
> >  
> >  /* Returns 1 when a valid ref has been added to `list`, 0 otherwise */
> > -static int process_ref_v2(struct packet_reader *reader, struct ref ***list)
> > +static int process_ref_v2(struct packet_reader *reader, struct ref ***list,
> > +			  char **unborn_head_target)
> >  {
> >  	int ret = 1;
> >  	int i = 0;
> > @@ -397,6 +398,25 @@ static int process_ref_v2(struct packet_reader *reader, struct ref ***list)
> >  		goto out;
> >  	}
> >  
> > +	if (!strcmp("unborn", line_sections.items[i].string)) {
> > +		i++;
> > +		if (unborn_head_target &&
> > +		    !strcmp("HEAD", line_sections.items[i++].string)) {
> > +			/*
> > +			 * Look for the symref target (if any). If found,
> > +			 * return it to the caller.
> > +			 */
> > +			for (; i < line_sections.nr; i++) {
> > +				const char *arg = line_sections.items[i].string;
> > +
> > +				if (skip_prefix(arg, "symref-target:", &arg)) {
> > +					*unborn_head_target = xstrdup(arg);
> > +					break;
> > +				}
> > +			}
> > +		}
> > +		goto out;
> > +	}
> 
> We split the line and notice that the first token is "unborn"; if
> the caller is not interested in the unborn head, we just skip the
> rest, but otherwise, if it is about HEAD (i.e. we do not care if a
> dangling symref that is not HEAD is reported), we notice the target
> in unborn_head_target.
> 
> OK.  We already saw how this is used in cmd_clone().
> 
> > @@ -461,6 +481,8 @@ struct ref **get_remote_refs(int fd_out, struct packet_reader *reader,
> >  	const char *hash_name;
> >  	struct strvec *ref_prefixes = transport_options ?
> >  		&transport_options->ref_prefixes : NULL;
> > +	char **unborn_head_target = transport_options ?
> > +		&transport_options->unborn_head_target : NULL;
> 
> So any caller that passes transport_options will get the unborn head
> information for free?  The other callers are in fetch-pack.c and
> transport.c, which presumably are about fetching and not cloning.
> 
> I recall discussions on filling a missing refs/remotes/X/HEAD when
> we fetch from X and learn where X points at.  Such an extension can
> be done on top of this mechanism to pass transport_options from the
> fetch codepath, I presume?

I don't recall those discussions, but I think that we can do that (as
long as HEAD points to a branch that is part of the refspec we're
fetching, because the ref-prefix check still applies).

> Thanks.  I tried to follow the thought in the patches aloud, and it
> was mostly a pleasant read.

Thanks.