8022795: Method.isVarargs of dynamic proxy generated method to match the proxy interface method

Reviewed-by: rriggs, darcy

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

@@ -670,7 +670,10 @@ final class ProxyGenerator extends ClassWriter {
         private void generateMethod(ClassWriter cw, String className) {
             MethodType mt = MethodType.methodType(returnType, parameterTypes);
             String desc = mt.toMethodDescriptorString();
-            MethodVisitor mv = cw.visitMethod(ACC_PUBLIC | ACC_FINAL,
+            int accessFlags = ACC_PUBLIC | ACC_FINAL;
+            if (method.isVarArgs()) accessFlags |= ACC_VARARGS;
+
+            MethodVisitor mv = cw.visitMethod(accessFlags,
                     method.getName(), desc, null,
                     typeNames(Arrays.asList(exceptionTypes)));
 

test/jdk/java/lang/reflect/Proxy/TestVarArgs.java

@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) 2020, 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 8022795
+ * @run testng TestVarArgs
+ * @summary Verify if a method defined in a proxy interface has ACC_VARARGS set
+ */
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Method;
+import java.lang.reflect.Proxy;
+import java.util.Arrays;
+
+import org.testng.annotations.DataProvider;
+import org.testng.annotations.Test;
+import static org.testng.Assert.*;
+
+public class TestVarArgs {
+    interface I {
+        Object call(Object... values);
+    }
+    interface J {
+        Object call(Object[] values);
+    }
+
+    @DataProvider(name = "proxyInterfaces")
+    public Object[][] proxyInterfaces() {
+        return new Object[][] {
+             { new Class<?>[] { I.class }, true},
+             { new Class<?>[] { J.class }, false},
+             { new Class<?>[] { I.class, J.class }, true},
+             { new Class<?>[] { J.class, I.class }, false},
+        };
+    }
+
+    @Test(dataProvider = "proxyInterfaces")
+    public void testMethod(Class<?>[] proxyInterfaces, boolean isVarArgs) throws Throwable {
+        // check if the first proxy interface with the method named "call" declares var result
+        Method m = proxyInterfaces[0].getMethod("call", Object[].class);
+        assertTrue(m.isVarArgs() == isVarArgs);
+
+        // the method in the generated proxy class should match the method
+        // declared in the proxy interface
+        Object proxy = Proxy.newProxyInstance(TestVarArgs.class.getClassLoader(),
+                                              proxyInterfaces, IH);
+        Class<?> proxyClass = proxy.getClass();
+        assertTrue(Proxy.isProxyClass(proxyClass));
+        Method method = proxyClass.getMethod("call", Object[].class);
+        assertTrue(method.isVarArgs() == isVarArgs);
+
+        Object params = new Object[] { "foo", "bar", "goo" };
+        Object result;
+
+        // test reflection
+        result = method.invoke(proxy, params);
+        assertEquals(result, params);
+
+        // test method handle
+        MethodHandle mh = MethodHandles.lookup().findVirtual(proxyClass, "call",
+                      MethodType.methodType(Object.class, Object[].class));
+        assertTrue(mh.isVarargsCollector() == isVarArgs);
+        MethodHandle mhVarArity = mh;
+        MethodHandle mhFixedArity = mh;
+        if (isVarArgs) {
+            mhFixedArity = mh.asFixedArity();
+        } else {
+            mhVarArity = mh.asVarargsCollector(Object[].class);
+        }
+        result = mhVarArity.invoke(proxy, "foo", "bar", "goo");
+        assertEquals(result, params);
+
+        result = mhFixedArity.invoke(proxy, params);
+        assertEquals(result, params);
+
+        if (!isVarArgs) {
+            MethodType mt = MethodType.methodType(Object.class, Object.class, String.class, String.class, String.class);
+            mh = mh.asVarargsCollector(Object[].class).asType(mt);
+        }
+        result = mh.invoke(proxy, "foo", "bar", "goo");
+        assertEquals(result, params);
+    }
+
+    private static final InvocationHandler IH = new InvocationHandler() {
+        @Override
+        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
+            return args[0];
+        }
+    };
+
+}