Add helpers for enforcing _check() calls

See kaitai-io/kaitai_struct_python_runtime@fa6fbd5

Author: generalmimon

src/main/java/io/kaitai/struct/ConsistencyNotCheckedError.java

@@ -0,0 +1,35 @@
+/**
+ * Copyright 2015-2025 Kaitai Project: MIT license
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package io.kaitai.struct;
+
+/**
+ * Exception thrown by {@link KaitaiStruct.ReadWrite#_write()} when attempting
+ * to write an object whose consistency hasn't been checked
+ * ({@link KaitaiStruct.ReadWrite#_check()}) since the last modification.
+ */
+public class ConsistencyNotCheckedError extends RuntimeException {
+    public ConsistencyNotCheckedError(String message) {
+        super(message);
+    }
+}

src/main/java/io/kaitai/struct/KaitaiStruct.java

@@ -58,6 +58,13 @@ public ReadOnly(KaitaiStream _io) {
      * shortcut methods.
      */
     public abstract static class ReadWrite extends ReadOnly {
+        /**
+         * Indicates whether the object has been externally modified since the
+         * last known consistent state, meaning that the consistency of the
+         * object is unknown because it hasn't been checked.
+         */
+        protected boolean _dirty = true;
+
         public ReadWrite(KaitaiStream _io) {
             super(_io);
         }
@@ -80,5 +87,11 @@ public void _write_Seq(KaitaiStream io) {
             this._io = io;
             _write_Seq();
         }
+
+        protected void _assertNotDirty() {
+            if (_dirty) {
+                throw new ConsistencyNotCheckedError("consistency not checked: _check() has not been called since the last modification of the object");
+            }
+        }
     }
 }