8354908: javac mishandles supplementary character in character literal

Reviewed-by: naoto, vromero

Author: lahodaj

src/jdk.compiler/share/classes/com/sun/tools/javac/parser/JavaTokenizer.java

@@ -389,6 +389,10 @@ private void scanLitChar(int pos, boolean isString) {
                     break;
             }
         } else {
+            if (!isString && !Character.isBmpCodePoint(getCodepoint())) {
+                lexError(pos, Errors.IllegalCharLiteralMultipleSurrogates);
+            }
+
             putThenNext();
         }
     }

src/jdk.compiler/share/classes/com/sun/tools/javac/resources/compiler.properties

@@ -694,6 +694,9 @@ compiler.err.illegal.combination.of.modifiers=\
 compiler.err.illegal.enum.static.ref=\
     illegal reference to static field from initializer
 
+compiler.err.illegal.char.literal.multiple.surrogates=\
+    character literal contains more than one UTF-16 code unit
+
 compiler.err.illegal.esc.char=\
     illegal escape character
 

test/langtools/tools/javac/diags/examples/IllegalCharLiteralMultipleSurrogates.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+// key: compiler.err.illegal.char.literal.multiple.surrogates
+
+class IllegalCharLiteralMultipleSurrogates {
+    char c = '\uD83D\uDE0A';
+}

test/langtools/tools/javac/lexer/JavaLexerTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -30,8 +30,11 @@
  */
 
 import java.net.URI;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Objects;
 
+import javax.tools.DiagnosticListener;
 import javax.tools.SimpleJavaFileObject;
 
 import com.sun.tools.javac.parser.JavaTokenizer;
@@ -101,17 +104,29 @@ public class JavaLexerTest {
             new TestTuple(ERROR,         "\'\'"),
             new TestTuple(ERROR,         "\'\\q\'", "\'\\q\'"),
             new TestTuple(ERROR,         "\'\\{1+2}\'", "\'\\{1+2}\'"),
+            new TestTuple(ERROR,         "'\uD83D\uDE0A'",
+                          List.of("compiler.err.illegal.char.literal.multiple.surrogates")),
     };
 
     static class TestTuple {
         String input;
         TokenKind kind;
         String expected;
+        List<String> expectedErrors;
 
-        TestTuple(TokenKind kind, String input, String expected) {
+        TestTuple(TokenKind kind, String input, String expected, List<String> expectedErrors) {
             this.input = input;
             this.kind = kind;
             this.expected = expected;
+            this.expectedErrors = expectedErrors;
+        }
+
+        TestTuple(TokenKind kind, String input, List<String> expectedErrors) {
+            this(kind, input, input, expectedErrors);
+        }
+
+        TestTuple(TokenKind kind, String input, String expected) {
+            this(kind, input, expected, null);
         }
 
         TestTuple(TokenKind kind, String input) {
@@ -121,6 +136,12 @@ static class TestTuple {
 
     void test(TestTuple test, boolean willFail) throws Exception {
         Context ctx = new Context();
+        List<String> errors = new ArrayList();
+
+        if (test.expectedErrors != null) {
+            ctx.put(DiagnosticListener.class, (DiagnosticListener) d -> errors.add(d.getCode()));
+        }
+
         Log log = Log.instance(ctx);
 
         log.useSource(SimpleJavaFileObject.forSource(URI.create("mem://Test.java"),
@@ -149,6 +170,10 @@ void test(TestTuple test, boolean willFail) throws Exception {
             System.err.println("input: " + test.input);
             throw new AssertionError("Unexpected token content: " + actual);
         }
+
+        if (test.expectedErrors != null && !test.expectedErrors.equals(errors)) {
+            throw new AssertionError("Unexpected errors: " + errors);
+        }
     }
 
     void run() throws Exception {