[GR-65190]: Fix raw unicode escape decoder

PullRequest: graalpython/3823

Author: horakivo

graalpython/com.oracle.graal.python.test/src/tests/test_string.py

@@ -1204,3 +1204,9 @@ def test_str_from_mmap():
         mm.write(b"GraalPy")
         mm.seek(0)
         assert str(mm, encoding='utf-8') == 'GraalPy'
+
+
+def test_raw_unicode_escape_does_not_alter_encoded_string():
+    original = "[\\xA0]"
+    decoded = bytes(original, encoding="raw-unicode-escape").decode("raw-unicode-escape")
+    assert original == decoded

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/charset/PythonRawUnicodeEscapeCharsetDecoder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * The Universal Permissive License (UPL), Version 1.0
@@ -75,6 +75,7 @@ protected CoderResult decodeLoop(ByteBuffer source, CharBuffer target) {
                     seenBackslash = false;
                 } else {
                     target.put('\\');
+                    target.put((char) (b & 0xFF));
                     seenBackslash = false;
                 }
             } else if (b == (byte) '\\') {