8372258: Improve TypeVariable support

Reviewed-by: liach

Author: minborg

src/java.base/share/classes/java/lang/reflect/TypeVariable.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2003, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2003, 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
@@ -72,7 +72,7 @@ public interface TypeVariable<D extends GenericDeclaration> extends Type, Annota
     Type[] getBounds();
 
     /**
-     * Returns the {@code GenericDeclaration} object representing the
+     * Returns a {@code GenericDeclaration} object representing the
      * generic declaration declared for this type variable.
      *
      * @return the generic declaration declared for this type variable.

src/java.base/share/classes/sun/reflect/generics/reflectiveObjects/TypeVariableImpl.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2003, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2003, 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
@@ -35,6 +35,8 @@
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Objects;
+
+import jdk.internal.reflect.ReflectionFactory;
 import sun.reflect.annotation.AnnotationSupport;
 import sun.reflect.annotation.TypeAnnotationParser;
 import sun.reflect.annotation.AnnotationType;
@@ -125,18 +127,24 @@ public Type[] getBounds() {
     }
 
     /**
-     * Returns the {@code GenericDeclaration} object representing the
+     * Returns a {@code GenericDeclaration} object representing the
      * generic declaration that declared this type variable.
      *
-     * @return the generic declaration that declared this type variable.
+     * @return a generic declaration that declared this type variable.
      *
      * @since 1.5
      */
+    @SuppressWarnings("unchecked")
     public D getGenericDeclaration() {
         assert genericDeclaration instanceof Class<?> ||
                 genericDeclaration instanceof Method ||
                 genericDeclaration instanceof Constructor : "Unexpected kind of GenericDeclaration";
-        return genericDeclaration;
+        // If the `genericDeclaration` instance is mutable, we need to make a copy.
+        return switch (genericDeclaration) {
+            case Method method       -> (D) ReflectionFactory.getReflectionFactory().copyMethod(method);
+            case Constructor<?> ctor -> (D) ReflectionFactory.getReflectionFactory().copyConstructor(ctor);
+            default -> genericDeclaration;
+        };
     }
 
 

test/jdk/java/lang/reflect/Generics/ProtectInnerStateOfTypeVariableImplTest.java

@@ -0,0 +1,70 @@
+/*
+ * 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.
+ */
+
+/*
+ * @test
+ * @bug 8372258
+ * @summary Test if a copy of the internal state is provided
+ * @run junit ProtectInnerStateOfTypeVariableImplTest
+ */
+
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Method;
+import java.lang.reflect.TypeVariable;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+final class ProtectInnerStateOfTypeVariableImplTest {
+
+    static final class Foo {
+        public <X> Foo() {
+        }
+
+        <X> X x() {
+            return null;
+        }
+    }
+
+    @Test
+    void testMethod() throws NoSuchMethodException {
+        Method method = Foo.class.getDeclaredMethod("x");
+        TypeVariable<Method> tv = method.getTypeParameters()[0];
+
+        Method gd = tv.getGenericDeclaration();
+        Method gd2 = tv.getGenericDeclaration();
+        assertNotSame(gd, gd2);
+    }
+
+    @Test
+    void testConstructor() throws NoSuchMethodException {
+        Constructor<?> ctor = Foo.class.getConstructor();
+        TypeVariable<? extends Constructor<?>> tv = ctor.getTypeParameters()[0];
+
+        Constructor<?> gd = tv.getGenericDeclaration();
+        Constructor<?> gd2 = tv.getGenericDeclaration();
+        assertNotSame(gd, gd2);
+    }
+
+}