expose a helper function peel_to_type().

This helper function is the core of "$object^{type}" parser.
Now it is made available to callers outside sha1_name.c

cache.h

@@ -499,6 +499,9 @@ extern void *read_object_with_reference(const unsigned char *sha1,
 					unsigned long *size,
 					unsigned char *sha1_ret);
 
+extern struct object *peel_to_type(const char *name, int namelen,
+				   struct object *o, enum object_type);
+
 enum date_mode {
 	DATE_NORMAL = 0,
 	DATE_RELATIVE,

sha1_name.c

@@ -423,6 +423,37 @@ static int get_nth_ancestor(const char *name, int len,
 	return 0;
 }
 
+struct object *peel_to_type(const char *name, int namelen,
+			    struct object *o, enum object_type expected_type)
+{
+	if (name && !namelen)
+		namelen = strlen(name);
+	if (!o) {
+		unsigned char sha1[20];
+		if (get_sha1_1(name, namelen, sha1))
+			return NULL;
+		o = parse_object(sha1);
+	}
+	while (1) {
+		if (!o || (!o->parsed && !parse_object(o->sha1)))
+			return NULL;
+		if (o->type == expected_type)
+			return o;
+		if (o->type == OBJ_TAG)
+			o = ((struct tag*) o)->tagged;
+		else if (o->type == OBJ_COMMIT)
+			o = &(((struct commit *) o)->tree->object);
+		else {
+			if (name)
+				error("%.*s: expected %s type, but the object "
+				      "dereferences to %s type",
+				      namelen, name, typename(expected_type),
+				      typename(o->type));
+			return NULL;
+		}
+	}
+}
+
 static int peel_onion(const char *name, int len, unsigned char *sha1)
 {
 	unsigned char outer[20];
@@ -474,29 +505,17 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 		hashcpy(sha1, o->sha1);
 	}
 	else {
-		/* At this point, the syntax look correct, so
+		/*
+		 * At this point, the syntax look correct, so
 		 * if we do not get the needed object, we should
 		 * barf.
 		 */
-
-		while (1) {
-			if (!o || (!o->parsed && !parse_object(o->sha1)))
-				return -1;
-			if (o->type == expected_type) {
-				hashcpy(sha1, o->sha1);
-				return 0;
-			}
-			if (o->type == OBJ_TAG)
-				o = ((struct tag*) o)->tagged;
-			else if (o->type == OBJ_COMMIT)
-				o = &(((struct commit *) o)->tree->object);
-			else
-				return error("%.*s: expected %s type, but the object dereferences to %s type",
-					     len, name, typename(expected_type),
-					     typename(o->type));
-			if (!o->parsed)
-				parse_object(o->sha1);
+		o = peel_to_type(name, len, o, expected_type);
+		if (o) {
+			hashcpy(sha1, o->sha1);
+			return 0;
 		}
+		return -1;
 	}
 	return 0;
 }