core: Move NodePath out of the transformation package

core/src/main/java/org/spongepowered/configurate/AbstractConfigurationNode.java

@@ -23,7 +23,6 @@
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.spongepowered.configurate.serialize.SerializationException;
 import org.spongepowered.configurate.serialize.TypeSerializer;
-import org.spongepowered.configurate.transformation.NodePath;
 import org.spongepowered.configurate.util.UnmodifiableCollections;
 
 import java.lang.reflect.Type;

core/src/main/java/org/spongepowered/configurate/ConfigurateException.java

@@ -17,7 +17,6 @@
 package org.spongepowered.configurate;
 
 import org.checkerframework.checker.nullness.qual.Nullable;
-import org.spongepowered.configurate.transformation.NodePath;
 
 import java.io.IOException;
 import java.util.function.Supplier;

core/src/main/java/org/spongepowered/configurate/ConfigurationNode.java

@@ -27,7 +27,6 @@
 import org.spongepowered.configurate.serialize.Scalars;
 import org.spongepowered.configurate.serialize.SerializationException;
 import org.spongepowered.configurate.serialize.TypeSerializer;
-import org.spongepowered.configurate.transformation.NodePath;
 
 import java.lang.reflect.Type;
 import java.util.Collection;

core/src/main/java/org/spongepowered/configurate/transformation/NodePath.java → core/src/main/java/org/spongepowered/configurate/NodePath.java

@@ -14,7 +14,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.spongepowered.configurate.transformation;
+package org.spongepowered.configurate;
 
 import java.util.Collection;
 import java.util.Iterator;
@@ -34,7 +34,11 @@ public interface NodePath extends Iterable<Object> {
      * @since 4.0.0
      */
     static NodePath of(Object[] path) {
-        return new NodePathImpl(path, true);
+        if (path.length == 0) {
+            return NodePathImpl.EMPTY;
+        } else {
+            return new NodePathImpl(path, true);
+        }
     }
 
     /**
@@ -45,7 +49,11 @@ static NodePath of(Object[] path) {
      * @since 4.0.0
      */
     static NodePath of(Collection<?> path) {
-        return new NodePathImpl(path.toArray(), false);
+        if (path.isEmpty()) {
+            return NodePathImpl.EMPTY;
+        } else {
+            return new NodePathImpl(path.toArray(), false);
+        }
     }
 
     /**

core/src/main/java/org/spongepowered/configurate/transformation/NodePathImpl.java → core/src/main/java/org/spongepowered/configurate/NodePathImpl.java

@@ -14,11 +14,11 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.spongepowered.configurate.transformation;
+package org.spongepowered.configurate;
 
 import static java.util.Objects.requireNonNull;
 
-import com.google.errorprone.annotations.concurrent.LazyInit;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 import java.util.Arrays;
 import java.util.Iterator;
@@ -27,11 +27,7 @@ final class NodePathImpl implements NodePath {
 
     static final NodePath EMPTY = new NodePathImpl(new Object[0], false);
 
-    @LazyInit Object[] arr;
-
-    NodePathImpl() {
-
-    }
+    private final Object[] arr;
 
     NodePathImpl(final Object[] arr, final boolean copy) {
         requireNonNull(arr);
@@ -88,16 +84,16 @@ public NodePath copy() {
     }
 
     @Override
-    public boolean equals(final Object o) {
-        if (this == o) {
+    public boolean equals(final @Nullable Object other) {
+        if (this == other) {
             return true;
         }
 
-        if (o == null || getClass() != o.getClass()) {
+        if (other == null || getClass() != other.getClass()) {
             return false;
         }
 
-        final NodePathImpl that = (NodePathImpl) o;
+        final NodePathImpl that = (NodePathImpl) other;
         return Arrays.equals(this.arr, that.arr);
     }
 

core/src/main/java/org/spongepowered/configurate/reference/ConfigurationReference.java

@@ -20,12 +20,12 @@
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.spongepowered.configurate.ConfigurateException;
 import org.spongepowered.configurate.ConfigurationNode;
+import org.spongepowered.configurate.NodePath;
 import org.spongepowered.configurate.ScopedConfigurationNode;
 import org.spongepowered.configurate.loader.ConfigurationLoader;
 import org.spongepowered.configurate.reactive.Publisher;
 import org.spongepowered.configurate.reactive.TransactionalSubscriber;
 import org.spongepowered.configurate.serialize.SerializationException;
-import org.spongepowered.configurate.transformation.NodePath;
 
 import java.nio.file.Path;
 import java.util.Map;

core/src/main/java/org/spongepowered/configurate/reference/ManualConfigurationReference.java

@@ -23,12 +23,12 @@
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.spongepowered.configurate.ConfigurateException;
 import org.spongepowered.configurate.ConfigurationNode;
+import org.spongepowered.configurate.NodePath;
 import org.spongepowered.configurate.ScopedConfigurationNode;
 import org.spongepowered.configurate.loader.ConfigurationLoader;
 import org.spongepowered.configurate.reactive.Processor;
 import org.spongepowered.configurate.reactive.Publisher;
 import org.spongepowered.configurate.serialize.SerializationException;
-import org.spongepowered.configurate.transformation.NodePath;
 
 import java.util.Map;
 import java.util.concurrent.Executor;

core/src/main/java/org/spongepowered/configurate/reference/ValueReferenceImpl.java

@@ -19,6 +19,7 @@
 import io.leangen.geantyref.TypeToken;
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.spongepowered.configurate.ConfigurateException;
+import org.spongepowered.configurate.NodePath;
 import org.spongepowered.configurate.ScopedConfigurationNode;
 import org.spongepowered.configurate.reactive.Disposable;
 import org.spongepowered.configurate.reactive.Publisher;
@@ -27,7 +28,6 @@
 import org.spongepowered.configurate.reference.ConfigurationReference.ErrorPhase;
 import org.spongepowered.configurate.serialize.SerializationException;
 import org.spongepowered.configurate.serialize.TypeSerializer;
-import org.spongepowered.configurate.transformation.NodePath;
 import org.spongepowered.configurate.util.UnmodifiableCollections;
 
 import java.util.concurrent.Executor;

core/src/main/java/org/spongepowered/configurate/serialize/SerializationException.java

@@ -19,7 +19,7 @@
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.spongepowered.configurate.ConfigurateException;
 import org.spongepowered.configurate.ConfigurationNode;
-import org.spongepowered.configurate.transformation.NodePath;
+import org.spongepowered.configurate.NodePath;
 
 import java.lang.reflect.Type;
 

core/src/main/java/org/spongepowered/configurate/transformation/ConfigurationTransformation.java

@@ -21,6 +21,7 @@
 import org.checkerframework.checker.nullness.qual.NonNull;
 import org.spongepowered.configurate.ConfigurateException;
 import org.spongepowered.configurate.ConfigurationNode;
+import org.spongepowered.configurate.NodePath;
 
 import java.util.NavigableMap;
 import java.util.TreeMap;

core/src/main/java/org/spongepowered/configurate/transformation/MutableNodePath.java

@@ -0,0 +1,67 @@
+/*
+ * 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.transformation;
+
+import com.google.errorprone.annotations.concurrent.LazyInit;
+import org.spongepowered.configurate.NodePath;
+
+import java.util.Arrays;
+import java.util.Iterator;
+
+/**
+ * Mutable implementation of {@link NodePath} for use with transform instances.
+ */
+final class MutableNodePath implements NodePath {
+
+    @LazyInit Object[] arr;
+
+    @Override
+    public Object get(final int i) {
+        return this.arr[i];
+    }
+
+    @Override
+    public int size() {
+        return this.arr.length;
+    }
+
+    @Override
+    public Object[] array() {
+        return Arrays.copyOf(this.arr, this.arr.length);
+    }
+
+    @Override
+    public NodePath withAppendedChild(final Object childKey) {
+        return copy().withAppendedChild(childKey);
+    }
+
+    @Override
+    public NodePath with(final int index, final Object value) throws IndexOutOfBoundsException {
+        return copy().with(index, value);
+    }
+
+    @Override
+    public Iterator<Object> iterator() {
+        return Arrays.asList(this.arr).iterator();
+    }
+
+    @Override
+    public NodePath copy() {
+        return NodePath.path(this.arr);
+    }
+
+}

core/src/main/java/org/spongepowered/configurate/transformation/NodePathComparator.java

@@ -18,6 +18,8 @@
 
 import static org.spongepowered.configurate.transformation.ConfigurationTransformation.WILDCARD_OBJECT;
 
+import org.spongepowered.configurate.NodePath;
+
 import java.util.Comparator;
 
 final class NodePathComparator implements Comparator<NodePath> {

core/src/main/java/org/spongepowered/configurate/transformation/SingleConfigurationTransformation.java

@@ -19,6 +19,7 @@
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.spongepowered.configurate.ConfigurateException;
 import org.spongepowered.configurate.ConfigurationNode;
+import org.spongepowered.configurate.NodePath;
 
 import java.util.Arrays;
 import java.util.List;
@@ -42,7 +43,7 @@ final class SingleConfigurationTransformation implements ConfigurationTransforma
      * <p>As such, data within paths is only guaranteed to be the same during a
      * run of a transform function.
      */
-    private final ThreadLocal<NodePathImpl> sharedPath = ThreadLocal.withInitial(NodePathImpl::new);
+    private final ThreadLocal<MutableNodePath> sharedPath = ThreadLocal.withInitial(MutableNodePath::new);
 
     SingleConfigurationTransformation(final Map<NodePath, TransformAction> actions, final MoveStrategy strategy) {
         this.actions = actions;
@@ -117,7 +118,7 @@ private void applySingleAction(final ConfigurationNode start, final Object[] pat
         }
 
         // apply action
-        final NodePathImpl nodePath = this.sharedPath.get();
+        final MutableNodePath nodePath = this.sharedPath.get();
         nodePath.arr = path;
 
         final Object @Nullable [] transformedPath = action.visitPath(nodePath, node);

core/src/main/java/org/spongepowered/configurate/transformation/TransformAction.java

@@ -20,6 +20,7 @@
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.spongepowered.configurate.ConfigurateException;
 import org.spongepowered.configurate.ConfigurationNode;
+import org.spongepowered.configurate.NodePath;
 
 import java.util.function.Supplier;
 

core/src/main/java/org/spongepowered/configurate/transformation/VersionedTransformation.java

@@ -19,6 +19,7 @@
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.spongepowered.configurate.ConfigurateException;
 import org.spongepowered.configurate.ConfigurationNode;
+import org.spongepowered.configurate.NodePath;
 
 import java.util.Map;
 import java.util.NavigableMap;

core/src/test/java/org/spongepowered/configurate/AbstractConfigurationNodeTest.java

@@ -31,7 +31,6 @@
 import org.junit.jupiter.api.Test;
 import org.spongepowered.configurate.objectmapping.ConfigSerializable;
 import org.spongepowered.configurate.serialize.SerializationException;
-import org.spongepowered.configurate.transformation.NodePath;
 import org.spongepowered.configurate.util.UnmodifiableCollections;
 
 import java.lang.reflect.Type;

core/src/test/java/org/spongepowered/configurate/transformation/ConfigurationTransformationTest.java

@@ -19,12 +19,13 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
-import static org.spongepowered.configurate.transformation.NodePath.path;
+import static org.spongepowered.configurate.NodePath.path;
 
 import org.junit.jupiter.api.Test;
 import org.spongepowered.configurate.BasicConfigurationNode;
 import org.spongepowered.configurate.ConfigurateException;
 import org.spongepowered.configurate.ConfigurationNode;
+import org.spongepowered.configurate.NodePath;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -50,7 +51,7 @@ private void doTestComparator(final ConfigurationNode node) throws ConfigurateEx
                 path("a", "b", "c", "d"),
                 path("a", "c"),
                 path("a", "b", "b")
-        );
+                                                         );
         final List<NodePath> autoSortedKeys = new ArrayList<>();
         final List<NodePath> expectedSortedKeys = Arrays.asList(
                 path("a", "b", "b"),

examples/src/main/java/org/spongepowered/configurate/examples/Transformations.java

@@ -16,7 +16,7 @@
  */
 package org.spongepowered.configurate.examples;
 
-import static org.spongepowered.configurate.transformation.NodePath.path;
+import static org.spongepowered.configurate.NodePath.path;
 
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.spongepowered.configurate.ConfigurateException;

examples/src/main/java/org/spongepowered/configurate/examples/ValueReferences.java

@@ -20,12 +20,12 @@
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.spongepowered.configurate.CommentedConfigurationNode;
 import org.spongepowered.configurate.ConfigurateException;
+import org.spongepowered.configurate.NodePath;
 import org.spongepowered.configurate.hocon.HoconConfigurationLoader;
 import org.spongepowered.configurate.objectmapping.ConfigSerializable;
 import org.spongepowered.configurate.reference.ConfigurationReference;
 import org.spongepowered.configurate.reference.ValueReference;
 import org.spongepowered.configurate.reference.WatchServiceListener;
-import org.spongepowered.configurate.transformation.NodePath;
 
 import java.io.IOException;
 import java.nio.file.Path;

extra/dfu3/src/main/java/org/spongepowered/configurate/extra/dfu/v3/DataFixerTransformation.java

@@ -26,8 +26,8 @@
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.spongepowered.configurate.ConfigurateException;
 import org.spongepowered.configurate.ConfigurationNode;
+import org.spongepowered.configurate.NodePath;
 import org.spongepowered.configurate.transformation.ConfigurationTransformation;
-import org.spongepowered.configurate.transformation.NodePath;
 
 import java.util.HashSet;
 import java.util.Set;

extra/dfu4/src/main/java/org/spongepowered/configurate/extra/dfu/v4/DataFixerTransformation.java

@@ -26,8 +26,8 @@
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.spongepowered.configurate.ConfigurateException;
 import org.spongepowered.configurate.ConfigurationNode;
+import org.spongepowered.configurate.NodePath;
 import org.spongepowered.configurate.transformation.ConfigurationTransformation;
-import org.spongepowered.configurate.transformation.NodePath;
 
 import java.util.HashSet;
 import java.util.Set;

extra/kotlin/src/main/kotlin/org/spongepowered/configurate/kotlin/extensions/ConfigurationNodeExtensions.kt

@@ -17,10 +17,10 @@
 package org.spongepowered.configurate.kotlin.extensions
 
 import org.spongepowered.configurate.ConfigurationNode
+import org.spongepowered.configurate.NodePath
 import org.spongepowered.configurate.ScopedConfigurationNode
 import org.spongepowered.configurate.kotlin.typeTokenOf
 import org.spongepowered.configurate.serialize.SerializationException
-import org.spongepowered.configurate.transformation.NodePath
 import kotlin.reflect.KClass
 
 /**

extra/kotlin/src/main/kotlin/org/spongepowered/configurate/kotlin/extensions/NodePathExtensions.kt

@@ -16,7 +16,7 @@
  */
 package org.spongepowered.configurate.kotlin.extensions
 
-import org.spongepowered.configurate.transformation.NodePath
+import org.spongepowered.configurate.NodePath
 
 /**
  * Concatenate [this] with another [NodePath].

format/gson/src/main/java/org/spongepowered/configurate/gson/GsonVisitor.java

@@ -23,7 +23,7 @@
 import org.spongepowered.configurate.ConfigurateException;
 import org.spongepowered.configurate.ConfigurationNode;
 import org.spongepowered.configurate.ConfigurationVisitor;
-import org.spongepowered.configurate.transformation.NodePath;
+import org.spongepowered.configurate.NodePath;
 
 import java.io.IOException;