Fabric: Introducing `LocalData` concept

Summary:
LocalData might be used to communicate some infomation between `ShadowNode`s
and native component views.

We will use it soon to store (and transmit to mounting layer) prepared for rendering attributed text in Text component.

Reviewed By: mdvacca

Differential Revision: D7738582

fbshipit-source-id: 1ead23ffd105cce0b3d9aeb9fc1d0df47673be50

ReactCommon/fabric/core/shadownode/LocalData.h

@@ -0,0 +1,36 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <fabric/core/Sealable.h>
+#include <fabric/debug/DebugStringConvertible.h>
+
+namespace facebook {
+namespace react {
+
+class LocalData;
+
+using SharedLocalData = std::shared_ptr<const LocalData>;
+
+/*
+ * Abstract class for any kind of concrete pieces of local data specific for
+ * some kinds of `ShadowNode`s.
+ * LocalData might be used to communicate some infomation between `ShadowNode`s
+ * and native component views.
+ * All `LocalData` objects *must* be immutable (sealed) when they became
+ * a part of the shadow tree.
+ */
+class LocalData:
+  public Sealable,
+  public DebugStringConvertible {
+
+  // Nothing.
+};
+
+} // namespace react
+} // namespace facebook

ReactCommon/fabric/core/shadownode/ShadowNode.cpp

@@ -47,6 +47,7 @@ ShadowNode::ShadowNode(
   props_(props ? props : shadowNode->props_),
   children_(std::make_shared<SharedShadowNodeList>(*(children ? children : shadowNode->children_))),
   sourceNode_(shadowNode),
+  localData_(shadowNode->localData_),
   cloneFunction_(shadowNode->cloneFunction_),
   revision_(shadowNode->revision_ + 1) {}
 
@@ -84,6 +85,10 @@ SharedShadowNode ShadowNode::getSourceNode() const {
   return sourceNode_.lock();
 }
 
+SharedLocalData ShadowNode::getLocalData() const {
+  return localData_;
+}
+
 void ShadowNode::sealRecursive() const {
   if (getSealed()) {
     return;
@@ -119,6 +124,11 @@ void ShadowNode::clearSourceNode() {
   sourceNode_.reset();
 }
 
+void ShadowNode::setLocalData(const SharedLocalData &localData) {
+  ensureUnsealed();
+  localData_ = localData;
+}
+
 void ShadowNode::shallowSourceNode() {
   ensureUnsealed();
 
@@ -135,7 +145,8 @@ bool ShadowNode::operator==(const ShadowNode& rhs) const {
   return
     tag_ == rhs.tag_ &&
     rootTag_ == rhs.rootTag_ &&
-    props_ == rhs.props_;
+    props_ == rhs.props_ &&
+    localData_ == rhs.localData_;
 }
 
 bool ShadowNode::operator!=(const ShadowNode& rhs) const {

ReactCommon/fabric/core/shadownode/ShadowNode.h

@@ -11,9 +11,10 @@
 #include <memory>
 #include <vector>
 
+#include <fabric/core/LocalData.h>
 #include <fabric/core/Props.h>
-#include <fabric/core/Sealable.h>
 #include <fabric/core/ReactPrimitives.h>
+#include <fabric/core/Sealable.h>
 #include <fabric/debug/DebugStringConvertible.h>
 
 namespace facebook {
@@ -80,6 +81,14 @@ public:
    */
   SharedShadowNode getSourceNode() const;
 
+  /*
+   * Returns a local data associated with the node.
+   * `LocalData` object might be used for data exchange between native view and
+   * shadow node instances.
+   * Concrete type of the object depends on concrete type of the `ShadowNode`.
+   */
+  SharedLocalData getLocalData() const;
+
   void sealRecursive() const;
 
 #pragma mark - Mutating Methods
@@ -88,11 +97,18 @@ public:
   void replaceChild(const SharedShadowNode &oldChild, const SharedShadowNode &newChild);
   void clearSourceNode();
 
+  /*
+   * Sets local data assosiated with the node.
+   * The node must be unsealed at this point.
+   */
+  void setLocalData(const SharedLocalData &localData);
+
   /*
    * Replaces the current source node with its source node.
    * This method might be used for illuminating side-effects caused by the last
    * cloning operation which are not desirable from the diffing algorithm
    * perspective.
+   * The node must be unsealed at this point.
    */
   void shallowSourceNode();
 
@@ -122,6 +138,7 @@ protected:
   SharedProps props_;
   SharedShadowNodeSharedList children_;
   WeakShadowNode sourceNode_;
+  SharedLocalData localData_;
 
 private:
 

ReactCommon/fabric/core/tests/ShadowNodeTest.cpp

@@ -150,3 +150,32 @@ TEST(ShadowNodeTest, handleCloneFunction) {
   ASSERT_EQ(secondNode->getRootTag(), secondNodeClone->getRootTag());
   ASSERT_EQ(secondNode->getProps(), secondNodeClone->getProps());
 }
+
+TEST(ShadowNodeTest, handleLocalData) {
+  auto localData42 = std::make_shared<TestLocalData>();
+  localData42->setNumber(42);
+
+  auto anotherLocalData42 = std::make_shared<TestLocalData>();
+  anotherLocalData42->setNumber(42);
+
+  auto localDataOver9000 = std::make_shared<TestLocalData>();
+  localDataOver9000->setNumber(9001);
+
+  auto firstNode = std::make_shared<TestShadowNode>(9, 1, (void *)NULL);
+  auto secondNode = std::make_shared<TestShadowNode>(9, 1, (void *)NULL);
+  auto thirdNode = std::make_shared<TestShadowNode>(9, 1, (void *)NULL);
+
+  firstNode->setLocalData(localData42);
+  secondNode->setLocalData(localData42);
+  thirdNode->setLocalData(localDataOver9000);
+
+  // LocalData object are compared by pointer, not by value.
+  ASSERT_EQ(*firstNode, *secondNode);
+  ASSERT_NE(*firstNode, *thirdNode);
+  secondNode->setLocalData(anotherLocalData42);
+  ASSERT_NE(*firstNode, *secondNode);
+
+  // LocalData cannot be changed for sealed shadow node.
+  secondNode->sealRecursive();
+  ASSERT_ANY_THROW(secondNode->setLocalData(localDataOver9000));
+}

ReactCommon/fabric/core/tests/TestComponent.h

@@ -11,6 +11,7 @@
 
 #include <fabric/core/ConcreteComponentDescriptor.h>
 #include <fabric/core/ConcreteShadowNode.h>
+#include <fabric/core/LocalData.h>
 #include <fabric/core/ShadowNode.h>
 
 using namespace facebook::react;
@@ -20,6 +21,20 @@ using namespace facebook::react;
  * To be used for testing purpose.
  */
 
+class TestLocalData: public LocalData {
+public:
+  void setNumber(const int &number) {
+    number_ = number;
+  }
+
+  int getNumber() const {
+    return number_;
+  }
+
+private:
+  int number_ {0};
+};
+
 class TestProps : public Props {
 public:
   TestProps() {