refs: add ref_type function

Add a function ref_type, which categorizes refs as per-worktree,
pseudoref, or normal ref.

Later, we will use this in refs.c to treat pseudorefs specially.
Alternate ref backends may use it to treat both pseudorefs and
per-worktree refs differently.

Signed-off-by: David Turner <dturner@twopensource.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -2821,6 +2821,32 @@ static int delete_ref_loose(struct ref_lock *lock, int flag, struct strbuf *err)
 	return 0;
 }
 
+static int is_per_worktree_ref(const char *refname)
+{
+	return !strcmp(refname, "HEAD");
+}
+
+static int is_pseudoref_syntax(const char *refname)
+{
+	const char *c;
+
+	for (c = refname; *c; c++) {
+		if (!isupper(*c) && *c != '-' && *c != '_')
+			return 0;
+	}
+
+	return 1;
+}
+
+enum ref_type ref_type(const char *refname)
+{
+	if (is_per_worktree_ref(refname))
+		return REF_TYPE_PER_WORKTREE;
+	if (is_pseudoref_syntax(refname))
+		return REF_TYPE_PSEUDOREF;
+       return REF_TYPE_NORMAL;
+}
+
 int delete_ref(const char *refname, const unsigned char *sha1, unsigned int flags)
 {
 	struct ref_transaction *transaction;