add common fsck error printing function

Signed-off-by: Martin Koegler <mkoegler@auto.tuwien.ac.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

fsck.c

@@ -304,3 +304,32 @@ int fsck_object(struct object *obj, int strict, fsck_error error_func)
 	return error_func(obj, FSCK_ERROR, "unknown type '%d' (internal fsck error)",
 			  obj->type);
 }
+
+int fsck_error_function(struct object *obj, int type, const char *fmt, ...)
+{
+	va_list ap;
+	int len;
+	struct strbuf sb;
+
+	strbuf_init(&sb, 0);
+	strbuf_addf(&sb, "object %s:", obj->sha1?sha1_to_hex(obj->sha1):"(null)");
+
+	va_start(ap, fmt);
+	len = vsnprintf(sb.buf + sb.len, strbuf_avail(&sb), fmt, ap);
+	va_end(ap);
+
+	if (len < 0)
+		len = 0;
+	if (len >= strbuf_avail(&sb)) {
+		strbuf_grow(&sb, len + 2);
+		va_start(ap, fmt);
+		len = vsnprintf(sb.buf + sb.len, strbuf_avail(&sb), fmt, ap);
+		va_end(ap);
+		if (len >= strbuf_avail(&sb))
+			die("this should not happen, your snprintf is broken");
+	}
+
+	error(sb.buf);
+	strbuf_release(&sb);
+	return 1;
+}

fsck.h

@@ -17,6 +17,8 @@ typedef int (*fsck_walk_func)(struct object *obj, int type, void *data);
 /* callback for fsck_object, type is FSCK_ERROR or FSCK_WARN */
 typedef int (*fsck_error)(struct object *obj, int type, const char *err, ...);
 
+int fsck_error_function(struct object *obj, int type, const char *fmt, ...);
+
 /* descend in all linked child objects
  * the return value is:
  *    -1	error in processing the object