A crude sketch for Lookup.unreflectDeconstructor (openjdk#7)

* A crude sketch of unreflect for deconstructors.

* Reuse the same mangling everywhere.

* Cleanup.

Author: lahodaj

src/java.base/share/classes/java/lang/invoke/MethodHandles.java

@@ -68,6 +68,8 @@
 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
 import static java.lang.invoke.MethodHandleStatics.newInternalError;
 import static java.lang.invoke.MethodType.methodType;
+import java.lang.reflect.Deconstructor;
+import java.lang.runtime.Carriers;
 
 /**
  * This class consists exclusively of static methods that operate on or return
@@ -3507,6 +3509,53 @@ public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessE
             return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
         }
 
+        /**
+         * Produces a method handle for a reflected deconstructor.
+         * TBD
+         * @param d the reflected deconstructor
+         * @return a method handle which can invoke the reflected deconstructor
+         * @throws IllegalAccessException if access checking fails
+         * @throws NullPointerException if the argument is null
+         */
+        public MethodHandle unreflectDeconstructor(Deconstructor<?> d) throws IllegalAccessException {
+            try {
+                String mangled = SharedSecrets.getJavaLangReflectAccess().getMangledName(d);
+                Method deconstructorMethod = d.getDeclaringClass().getDeclaredMethod(mangled, d.getDeclaringClass());
+                MethodHandle deconstructorPhysicalHandle = unreflect(deconstructorMethod);
+                List<Class<?>> methodTypeTypes = new ArrayList<>();
+                methodTypeTypes.add(Object.class);
+                MethodType bindingMethodType = MethodType.methodType(Object.class, Arrays.stream(d.getPatternBindings())
+                                                                                         .map(b -> b.getType())
+                                                                                         .toArray(Class[]::new));
+                return MethodHandles.filterReturnValue(deconstructorPhysicalHandle, MethodHandles.insertArguments(CARRIER_TO_ARRAY, 1, Carriers.components(bindingMethodType)));
+            } catch (NoSuchMethodException | SecurityException ex) {
+                throw new InternalError(ex);
+            }
+        }
+
+        private static final MethodHandles.Lookup LOOKUP = MethodHandles.lookup();
+        private static MethodHandle CARRIER_TO_ARRAY;
+
+        static {
+            try {
+                CARRIER_TO_ARRAY = LOOKUP.findStatic(Lookup.class, "carrier2Array",
+                                               MethodType.methodType(Object[].class, Object.class, List.class));
+            } catch (ReflectiveOperationException e) {
+                throw new ExceptionInInitializerError(e);
+            }
+        }
+
+        private static Object[] carrier2Array(Object carrier, List<MethodHandle> componentHandles) throws Throwable {
+            Object[] result = new Object[componentHandles.size()];
+            int i = 0;
+
+            for (MethodHandle componentAccessor : componentHandles) {
+                result[i++] = componentAccessor.invoke(carrier);
+            }
+
+            return result;
+        }
+
         /*
          * Produces a method handle that is capable of creating instances of the given class
          * and instantiated by the given constructor.  No security manager check.

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

@@ -423,7 +423,7 @@ public int getPatternFlags() {
     public Object[] invoke(Object matchCandidate)
         throws IllegalAccessException, MatchException
     {
-        String underlyingName = mangle(this.getDeclaringClass(), Arrays.stream(getPatternBindings()).map(pb -> pb.getType()).toArray(Class[]::new));
+        String underlyingName = getMangledName();
 
         try {
             Method method = this.getDeclaringClass().getDeclaredMethod(underlyingName, matchCandidate.getClass());
@@ -472,4 +472,8 @@ public Annotation[] getDeclaredAnnotations()  {
     public AnnotatedType getAnnotatedReturnType() {
         return null;
     }
+
+    String getMangledName() {
+        return mangle(this.getDeclaringClass(), Arrays.stream(getPatternBindings()).map(pb -> pb.getType()).toArray(Class[]::new));
+    }
 }

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

@@ -131,4 +131,9 @@ public <T> T newInstance(Constructor<T> ctor, Object[] args, Class<?> caller)
     {
         return ctor.newInstanceWithCaller(args, true, caller);
     }
+
+    @Override
+    public String getMangledName(Deconstructor<?> d) {
+        return d.getMangledName();
+    }
 }

src/java.base/share/classes/jdk/internal/access/JavaLangReflectAccess.java

@@ -105,4 +105,6 @@ public void setConstructorAccessor(Constructor<?> c,
     /** Returns a new instance created by the given constructor with access check */
     public <T> T newInstance(Constructor<T> ctor, Object[] args, Class<?> caller)
         throws IllegalAccessException, InstantiationException, InvocationTargetException;
+
+    public String getMangledName(Deconstructor<?> d);
 }

test/jdk/java/lang/invoke/lookup/UnreflectPattern.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2024, 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
+ * @summary Verify unreflect works for deconstructors
+ * @enablePreview
+ * @compile UnreflectPattern.java
+ * @run main UnreflectPattern
+ */
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.reflect.Deconstructor;
+import java.util.Arrays;
+
+public class UnreflectPattern {
+
+    public static void main(String... args) throws Throwable {
+        Object[] expected = new Object[] {"correct", -1};
+        Object instance = new UnreflectPattern();
+        Deconstructor<?> deconstructor = UnreflectPattern.class.getDeclaredDeconstructor(String.class, int.class);
+        Object[] result1 = deconstructor.invoke(instance);
+        if (!Arrays.equals(expected, result1)) {
+            throw new AssertionError("Unexpected result: " + Arrays.toString(result1));
+        }
+        MethodHandle deconstructorHandle = MethodHandles.lookup().unreflectDeconstructor(deconstructor);
+        Object[] result2 = (Object[]) deconstructorHandle.invoke(instance);
+        if (!Arrays.equals(expected, result2)) {
+            throw new AssertionError("Unexpected result: " + Arrays.toString(result2));
+        }
+    }
+
+    public pattern UnreflectPattern(String s, int i) {
+        match UnreflectPattern("correct", -1);
+    }
+}