feat(core): Optionally use a user-provided Lookup when building object mappers

This allows Configurate to read fields in otherwise closed modules.

Author: zml2008

core/build.gradle

@@ -36,7 +36,7 @@ sourceSets {
     main {
         multirelease {
             alternateVersions(
-                // 9, // VarHandles // TODO: temporarily disabled, cannot write final fields
+                9, // private Lookup, ~~VarHandles~~ // TODO: handles temporarily disabled, cannot write final fields
                 10, // immutable collections
                 16 // FieldDiscoverer for records
             )

core/src/main/java/org/spongepowered/configurate/objectmapping/FieldDiscoverer.java

@@ -22,6 +22,7 @@
 import org.spongepowered.configurate.serialize.SerializationException;
 import org.spongepowered.configurate.util.CheckedFunction;
 
+import java.lang.invoke.MethodHandles;
 import java.lang.reflect.AnnotatedElement;
 import java.lang.reflect.AnnotatedType;
 import java.util.function.Supplier;
@@ -127,6 +128,31 @@ static FieldDiscoverer<?> emptyConstructorObject() {
         return ObjectFieldDiscoverer.EMPTY_CONSTRUCTOR_INSTANCE;
     }
 
+    /**
+     * Inspect the {@code target} type for fields to be supplied to
+     * the {@code collector}.
+     *
+     * <p>If the target type is handleable, a non-null value must be returned.
+     * Fields can only be collected from one source at the moment, so if the
+     * instance factory is null any discovered fields will be discarded.</p>
+     *
+     * @param target type to inspect
+     * @param collector collector for discovered fields.
+     * @param lookup a lookup for reflective access to access-controlled members
+     * @param <V> object type
+     * @return a factory for handling the construction of object instances, or
+     *      {@code null} if {@code target} is not of a handleable type.
+     * @throws SerializationException if any fields have invalid data
+     * @since 4.2.0
+     */
+    default <V> @Nullable InstanceFactory<I> discover(
+        final AnnotatedType target,
+        final FieldCollector<I, V> collector,
+        final MethodHandles.@Nullable Lookup lookup
+    ) throws SerializationException {
+        return this.discover(target, collector);
+    }
+
     /**
      * Inspect the {@code target} type for fields to be supplied to
      * the {@code collector}.
@@ -142,8 +168,16 @@ static FieldDiscoverer<?> emptyConstructorObject() {
      *      {@code null} if {@code target} is not of a handleable type.
      * @throws SerializationException if any fields have invalid data
      * @since 4.0.0
+     * @deprecated for removal since 4.2.0, use the module-aware
+     *     {@link #discover(AnnotatedType, FieldCollector, MethodHandles.Lookup)} instead
      */
-    <V> @Nullable InstanceFactory<I> discover(AnnotatedType target, FieldCollector<I, V> collector) throws SerializationException;
+    @Deprecated
+    default <V> @Nullable InstanceFactory<I> discover(
+        final AnnotatedType target,
+        final FieldCollector<I, V> collector
+    ) throws SerializationException {
+        return null;
+    }
 
     /**
      * A handler that controls the deserialization process for an object.

core/src/main/java/org/spongepowered/configurate/objectmapping/LookupShim.java

@@ -0,0 +1,30 @@
+/*
+ * Configurate
+ * Copyright (C) zml and Configurate contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.spongepowered.configurate.objectmapping;
+
+import java.lang.invoke.MethodHandles;
+
+final class LookupShim {
+
+    private LookupShim() {
+    }
+
+    static MethodHandles.Lookup privateLookupIn(final Class<?> clazz, final MethodHandles.Lookup existingLookup) throws IllegalAccessException {
+        return existingLookup.in(clazz);
+    }
+
+}

core/src/main/java/org/spongepowered/configurate/objectmapping/ObjectFieldDiscoverer.java

@@ -22,45 +22,73 @@
 
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.spongepowered.configurate.serialize.SerializationException;
+import org.spongepowered.configurate.util.CheckedBiFunction;
 import org.spongepowered.configurate.util.CheckedFunction;
 import org.spongepowered.configurate.util.Types;
 
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
 import java.lang.reflect.AnnotatedType;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Field;
-import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Modifier;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.function.Supplier;
 
-class ObjectFieldDiscoverer implements FieldDiscoverer<Map<Field, Object>> {
+class ObjectFieldDiscoverer implements FieldDiscoverer<Map<ObjectFieldDiscoverer.FieldHandles, Object>> {
 
-    static final ObjectFieldDiscoverer EMPTY_CONSTRUCTOR_INSTANCE = new ObjectFieldDiscoverer(type -> {
+    private static final MethodHandles.Lookup OWN_LOOKUP = MethodHandles.lookup();
+
+    static final ObjectFieldDiscoverer EMPTY_CONSTRUCTOR_INSTANCE = new ObjectFieldDiscoverer((type, lookup) -> {
         try {
-            final Constructor<?> constructor;
-            constructor = erase(type.getType()).getDeclaredConstructor();
-            constructor.setAccessible(true);
+            final MethodHandle constructor;
+            final Class<?> erased = erase(type.getType());
+            if (lookup == null) { // legacy
+                final Constructor<?> construct = erased.getDeclaredConstructor();
+                construct.setAccessible(true);
+                constructor = OWN_LOOKUP.unreflectConstructor(construct);
+            } else {
+                constructor = LookupShim.privateLookupIn(erased, lookup)
+                    .findConstructor(erased, MethodType.methodType(void.class));
+            }
+
             return () -> {
                 try {
-                    return constructor.newInstance();
-                } catch (final InstantiationException | IllegalAccessException | InvocationTargetException e) {
-                    throw new RuntimeException(e);
+                    return constructor.invoke();
+                } catch (final RuntimeException ex) {
+                    throw ex;
+                } catch (final Throwable thr) {
+                    throw new RuntimeException(thr);
                 }
             };
-        } catch (final NoSuchMethodException e) {
+        } catch (final NoSuchMethodException | IllegalAccessException e) {
             return null;
         }
     }, "Objects must have a zero-argument constructor to be able to create new instances", false);
 
-    private final CheckedFunction<AnnotatedType, @Nullable Supplier<Object>, SerializationException> instanceFactory;
+    private final CheckedBiFunction<
+        AnnotatedType,
+        MethodHandles.@Nullable Lookup,
+        @Nullable Supplier<Object>,
+        SerializationException
+        > instanceFactory;
     private final String instanceUnavailableErrorMessage;
     private final boolean requiresInstanceCreation;
 
     ObjectFieldDiscoverer(
         final CheckedFunction<AnnotatedType, @Nullable Supplier<Object>, SerializationException> instanceFactory,
         final @Nullable String instanceUnavailableErrorMessage,
         final boolean requiresInstanceCreation
+    ) {
+        this((type, lookup) -> instanceFactory.apply(type), instanceUnavailableErrorMessage, requiresInstanceCreation);
+    }
+
+    ObjectFieldDiscoverer(
+        final CheckedBiFunction<AnnotatedType, MethodHandles.@Nullable Lookup, @Nullable Supplier<Object>, SerializationException> instanceFactory,
+        final @Nullable String instanceUnavailableErrorMessage,
+        final boolean requiresInstanceCreation
     ) {
         this.instanceFactory = instanceFactory;
         if (instanceUnavailableErrorMessage == null) {
@@ -72,60 +100,65 @@ class ObjectFieldDiscoverer implements FieldDiscoverer<Map<Field, Object>> {
     }
 
     @Override
-    public <V> @Nullable InstanceFactory<Map<Field, Object>> discover(final AnnotatedType target,
-            final FieldCollector<Map<Field, Object>, V> collector) throws SerializationException {
+    public <V> @Nullable InstanceFactory<Map<FieldHandles, Object>> discover(
+        final AnnotatedType target,
+        final FieldCollector<Map<FieldHandles, Object>, V> collector,
+        final MethodHandles.@Nullable Lookup lookup
+    ) throws SerializationException {
         final Class<?> clazz = erase(target.getType());
         if (clazz.isInterface()) {
             throw new SerializationException(target.getType(), "ObjectMapper can only work with concrete types");
         }
 
-        final @Nullable Supplier<Object> maker = this.instanceFactory.apply(target);
+        final @Nullable Supplier<Object> maker = this.instanceFactory.apply(target, lookup);
         if (maker == null && this.requiresInstanceCreation) {
             return null;
         }
 
         AnnotatedType collectType = target;
         Class<?> collectClass = clazz;
         while (true) {
-            collectFields(collectType, collector);
+            collectFields(collectType, collector, lookup);
             collectClass = collectClass.getSuperclass();
             if (collectClass.equals(Object.class)) {
                 break;
             }
             collectType = getExactSuperType(collectType, collectClass);
         }
 
-        return new MutableInstanceFactory<Map<Field, Object>>() {
+        return new MutableInstanceFactory<Map<FieldHandles, Object>>() {
 
             @Override
-            public Map<Field, Object> begin() {
+            public Map<FieldHandles, Object> begin() {
                 return new HashMap<>();
             }
 
             @Override
-            public void complete(final Object instance, final Map<Field, Object> intermediate) throws SerializationException {
-                for (final Map.Entry<Field, Object> entry : intermediate.entrySet()) {
+            public void complete(final Object instance, final Map<FieldHandles, Object> intermediate) throws SerializationException {
+                for (final Map.Entry<FieldHandles, Object> entry : intermediate.entrySet()) {
                     try {
                         // Handle implicit field initialization by detecting any existing information in the object
                         if (entry.getValue() instanceof ImplicitProvider) {
                             final @Nullable Object implicit = ((ImplicitProvider) entry.getValue()).provider.get();
                             if (implicit != null) {
-                                if (entry.getKey().get(instance) == null) {
-                                    entry.getKey().set(instance, implicit);
+                                if (entry.getKey().getter.invoke(instance) == null) {
+                                    entry.getKey().setter.invoke(instance, implicit);
                                 }
                             }
                         } else {
-                            entry.getKey().set(instance, entry.getValue());
+                            entry.getKey().setter.invoke(instance, entry.getValue());
                         }
                     } catch (final IllegalAccessException e) {
                         throw new SerializationException(target.getType(), e);
+                    } catch (final Throwable thr) {
+                        throw new SerializationException(target.getType(), "An unexpected error occurred while trying to set a field", thr);
                     }
                 }
             }
 
             @Override
-            public Object complete(final Map<Field, Object> intermediate) throws SerializationException {
-                final Object instance = maker == null ? null : maker.get();
+            public Object complete(final Map<FieldHandles, Object> intermediate) throws SerializationException {
+                final @Nullable Object instance = maker == null ? null : maker.get();
                 if (instance == null) {
                     throw new SerializationException(target.getType(), ObjectFieldDiscoverer.this.instanceUnavailableErrorMessage);
                 }
@@ -141,22 +174,70 @@ public boolean canCreateInstances() {
         };
     }
 
-    private void collectFields(final AnnotatedType clazz, final FieldCollector<Map<Field, Object>, ?> fieldMaker) {
+    private <V> void collectFields(
+        final AnnotatedType clazz,
+        final FieldCollector<Map<FieldHandles, Object>, V> fieldMaker,
+        final MethodHandles.@Nullable Lookup lookup
+    ) throws SerializationException {
         for (final Field field : erase(clazz.getType()).getDeclaredFields()) {
             if ((field.getModifiers() & (Modifier.STATIC | Modifier.TRANSIENT)) != 0) {
                 continue;
             }
 
-            field.setAccessible(true);
             final AnnotatedType fieldType = getFieldType(field, clazz);
-            fieldMaker.accept(field.getName(), fieldType, Types.combinedAnnotations(fieldType, field),
-                              (intermediate, val, implicitProvider) -> {
-                    if (val != null) {
-                        intermediate.put(field, val);
-                    } else {
-                        intermediate.put(field, new ImplicitProvider(implicitProvider));
-                    }
-                }, field::get);
+            final FieldData.Deserializer<Map<FieldHandles, Object>> deserializer;
+            final CheckedFunction<V, @Nullable Object, Exception> serializer;
+            final FieldHandles handles;
+            try {
+                if (lookup != null) {
+                    handles = new FieldHandles(field, lookup);
+                } else {
+                    handles = new FieldHandles(field);
+                }
+            } catch (final IllegalAccessException ex) {
+                throw new SerializationException(fieldType, ex);
+            }
+            deserializer = (intermediate, val, implicitProvider) -> {
+                if (val != null) {
+                    intermediate.put(handles, val);
+                } else {
+                    intermediate.put(handles, new ImplicitProvider(implicitProvider));
+                }
+            };
+            serializer = inst -> {
+                try {
+                    return handles.getter.invoke(inst);
+                } catch (final Exception ex) {
+                    throw ex;
+                } catch (final Throwable thr) {
+                    throw new Exception(thr);
+                }
+            };
+            fieldMaker.accept(
+                field.getName(),
+                fieldType,
+                Types.combinedAnnotations(fieldType, field),
+                deserializer,
+                serializer
+            );
+        }
+    }
+
+    static class FieldHandles {
+        final MethodHandle getter;
+        final MethodHandle setter;
+
+        FieldHandles(final Field field) throws IllegalAccessException {
+            field.setAccessible(true);
+            final MethodHandles.Lookup lookup = MethodHandles.publicLookup();
+
+            this.getter = lookup.unreflectGetter(field);
+            this.setter = lookup.unreflectSetter(field);
+        }
+
+        FieldHandles(final Field field, final MethodHandles.Lookup lookup) throws IllegalAccessException {
+            this.getter = lookup.unreflectGetter(field);
+            this.setter = lookup.unreflectSetter(field);
         }
     }
 

core/src/main/java/org/spongepowered/configurate/objectmapping/ObjectMapper.java

@@ -28,6 +28,7 @@
 import org.spongepowered.configurate.util.NamingScheme;
 
 import java.lang.annotation.Annotation;
+import java.lang.invoke.MethodHandles;
 import java.lang.reflect.Type;
 import java.util.List;
 
@@ -361,6 +362,18 @@ default <A extends Annotation> Builder addConstraint(final Class<A> definition,
              */
             Builder addPostProcessor(PostProcessor.Factory factory);
 
+            /**
+             * Set a custom lookup to access fields.
+             *
+             * <p>This allows Configurate to reflectively modify classes
+             * without opening them for reflective access.</p>
+             *
+             * @param lookup the lookup to use
+             * @return this builder
+             * @since 4.2.0
+             */
+            Builder lookup(MethodHandles.Lookup lookup);
+
             /**
              * Create a new factory using the current configuration.
              *