Subject: Re: [PATCH v3 37/44] refs: break out a ref conflict check

From: David Turner <[email-masked]>
Date: Tue, 13 Oct 2015 14:46:31 -0400

On Tue, 2015-10-13 at 12:25 +0200, Michael Haggerty wrote:
> On 10/12/2015 11:51 PM, David Turner wrote:
> > Create new function verify_no_descendants, to hold one of the ref
> > conflict checks used in verify_refname_available.  Multiple backends
> > will need this function, so it goes in the common code.
> > 
> > Signed-off-by: David Turner <[email-masked]>
> > ---
> >  refs-be-files.c | 33 ++++++++-------------------------
> >  refs.c          | 22 ++++++++++++++++++++++
> >  refs.h          |  7 +++++++
> >  3 files changed, 37 insertions(+), 25 deletions(-)
> > 
> > [...]
> > diff --git a/refs.c b/refs.c
> > index 5a3125d..3ae0274 100644
> > --- a/refs.c
> > +++ b/refs.c
> > @@ -1101,6 +1101,28 @@ enum peel_status peel_object(const unsigned char *name, unsigned char *sha1)
> >  	return PEEL_PEELED;
> >  }
> >  
> > +const char *find_descendant_ref(const char *refname,
> > +				const struct string_list *extras,
> > +				const struct string_list *skip)
> > +{
> > +	int pos;
> > +	if (!extras)
> > +		return NULL;
> > +
> > +	/* Look for the place where "$refname/" would be inserted in extras. */
> 
> The comment above is misleading. See my note at the bottom of this email
> for an explanation.
> 
> > +	for (pos = string_list_find_insert_index(extras, refname, 0);
> > +	     pos < extras->nr; pos++) {
> > +		const char *extra_refname = extras->items[pos].string;
> > +
> > +		if (!starts_with(extra_refname, refname))
> > +			break;
> > +
> > +		if (!skip || !string_list_has_string(skip, extra_refname))
> > +			return extra_refname;
> > +	}
> > +	return NULL;
> > +}
> > +
> >  /* backend functions */
> >  int refs_initdb(struct strbuf *err, int shared)
> >  {
> > diff --git a/refs.h b/refs.h
> > index 3aad3b8..f8becea 100644
> > --- a/refs.h
> > +++ b/refs.h
> > @@ -637,6 +637,13 @@ int files_log_ref_write(const char *refname, const unsigned char *old_sha1,
> >  			const unsigned char *new_sha1, const char *msg,
> >  			int flags, struct strbuf *err);
> >  
> > +/*
> > + * Check for entries in extras that start with "$refname/", ignoring
> > + * those in skip. If there is such an entry, then we have a conflict.
> > + */
> > +const char *find_descendant_ref(const char *refname,
> > +				const struct string_list *extras,
> > +				const struct string_list *skip);
> 
> The documentation is is not correct. As written, the function needs not
> the refname as argument but the refname followed by '/'. Without the
> trailing slash, "refs/heads/foo" would be blocked by "refs/heads/foobar".
> 
> From the point of view of simplicity, it would be nice if this function
> could take a refname (without the trailing slash) as argument. But then
> it would basically be forced to allocate a new string, copy refname to
> it, append a '/', then free the string again when it's done.
> Alternatively, it could accept its refname argument in a strbuf and
> temporarily append the '/'.
> 
> But neither one of these alternatives is so elegant, so maybe it's OK if
> this function is documented to take a "directory name, including the
> trailing '/'" as argument and rename the argument (e.g., to "dirname").
> 
> Please also document that "skip" and "extras" can be NULL, but if not
> NULL they need to be sorted lists.

I think `extras` may not be NULL.  But I've otherwise fixed this.
Thanks.