remote: let guess_remote_head() optionally return all matches

Determining HEAD is ambiguous since it is done by comparing SHA1s.

In the case of multiple matches we return refs/heads/master if it
matches, else we return the first match we encounter. builtin-remote
needs all matches returned to it, so add a flag for it to request such.

To be simple and consistent, the return value is now a copy (including
peer_ref) of the matching refs.

Originally contributed by Jeff King along with the prior commit as a
single patch.

Signed-off-by: Jay Soffian <jaysoffian@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-clone.c

@@ -510,7 +510,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 		mapped_refs = write_remote_refs(refs, &refspec, reflog_msg.buf);
 
 		remote_head = find_ref_by_name(refs, "HEAD");
-		head_points_at = guess_remote_head(remote_head, mapped_refs);
+		head_points_at = guess_remote_head(remote_head, mapped_refs, 0);
 	}
 	else {
 		warning("You appear to have cloned an empty repository.");

remote.c

@@ -1460,24 +1460,33 @@ struct ref *get_local_heads(void)
 	return local_refs;
 }
 
-const struct ref *guess_remote_head(const struct ref *head,
-				    const struct ref *refs)
+struct ref *guess_remote_head(const struct ref *head,
+			      const struct ref *refs,
+			      int all)
 {
 	const struct ref *r;
+	struct ref *list = NULL;
+	struct ref **tail = &list;
 
 	if (!head)
 		return NULL;
 
 	/* If refs/heads/master could be right, it is. */
-	r = find_ref_by_name(refs, "refs/heads/master");
-	if (r && !hashcmp(r->old_sha1, head->old_sha1))
-		return r;
+	if (!all) {
+		r = find_ref_by_name(refs, "refs/heads/master");
+		if (r && !hashcmp(r->old_sha1, head->old_sha1))
+			return copy_ref(r);
+	}
 
 	/* Look for another ref that points there */
-	for (r = refs; r; r = r->next)
-		if (r != head && !hashcmp(r->old_sha1, head->old_sha1))
-			return r;
+	for (r = refs; r; r = r->next) {
+		if (r != head && !hashcmp(r->old_sha1, head->old_sha1)) {
+			*tail = copy_ref(r);
+			tail = &((*tail)->next);
+			if (!all)
+				break;
+		}
+	}
 
-	/* Nothing is the same */
-	return NULL;
+	return list;
 }

remote.h

@@ -139,12 +139,14 @@ int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs);
 int format_tracking_info(struct branch *branch, struct strbuf *sb);
 
 struct ref *get_local_heads(void);
-
 /*
- * Look for a ref in refs whose SHA1 matches head, first checking if
- * refs/heads/master matches. Return NULL if nothing matches or if head
- * is NULL.
+ * Find refs from a list which are likely to be pointed to by the given HEAD
+ * ref. If 'all' is false, returns the most likely ref; otherwise, returns a
+ * list of all candidate refs. If no match is found (or 'head' is NULL),
+ * returns NULL. All returns are newly allocated and should be freed.
  */
-const struct ref *guess_remote_head(const struct ref *head,
-				    const struct ref *refs);
+struct ref *guess_remote_head(const struct ref *head,
+			      const struct ref *refs,
+			      int all);
+
 #endif