Fabric: Improved signature of calculateMutationInstructions

Summary: Apparently, `calculateMutationInstructions` must also produce mutation instructions for root node as well. To make it possible we have to change the signature of the function and weak some restrictions in TreeMutationInstruction.

Reviewed By: fkgozali

Differential Revision: D7958248

fbshipit-source-id: 4109a6bce3a77f7eb89157201fd0e80f98487dbd

ReactCommon/fabric/uimanager/Differentiator.cpp

@@ -5,7 +5,7 @@
 namespace facebook {
 namespace react {
 
-void calculateMutationInstructions(
+static void calculateMutationInstructions(
   TreeMutationInstructionList &instructions,
   SharedShadowNode parentNode,
   SharedShadowNodeSharedList oldChildNodes,
@@ -154,5 +154,33 @@ void calculateMutationInstructions(
   instructions.insert(instructions.end(), downwardInstructions.begin(), downwardInstructions.end());
 }
 
+
+void calculateMutationInstructions(
+  TreeMutationInstructionList &instructions,
+  SharedShadowNode oldRootShadowNode,
+  SharedShadowNode newRootShadowNode
+) {
+  // Root shadow nodes must have same tag.
+  assert(oldRootShadowNode->getTag() == newRootShadowNode->getTag());
+
+  if (*oldRootShadowNode != *newRootShadowNode) {
+    instructions.push_back(
+      TreeMutationInstruction::Replace(
+        nullptr,
+        oldRootShadowNode,
+        newRootShadowNode,
+        -1
+      )
+    );
+  }
+
+  calculateMutationInstructions(
+    instructions,
+    oldRootShadowNode,
+    oldRootShadowNode->getChildren(),
+    newRootShadowNode->getChildren()
+  );
+}
+
 } // namespace react
 } // namespace facebook

ReactCommon/fabric/uimanager/Differentiator.h

@@ -15,9 +15,8 @@ namespace react {
  */
 void calculateMutationInstructions(
   TreeMutationInstructionList &instructions,
-  SharedShadowNode parentNode,
-  SharedShadowNodeSharedList oldChildNodes,
-  SharedShadowNodeSharedList newChildNodes
+  SharedShadowNode oldNode,
+  SharedShadowNode newNode
 );
 
 } // namespace react

ReactCommon/fabric/uimanager/ShadowTree.cpp

@@ -69,8 +69,7 @@ void ShadowTree::complete(UnsharedRootShadowNode newRootShadowNode) {
   calculateMutationInstructions(
     instructions,
     oldRootShadowNode,
-    oldRootShadowNode->ShadowNode::getChildren(),
-    newRootShadowNode->ShadowNode::getChildren()
+    newRootShadowNode
   );
 
   if (commit(newRootShadowNode)) {

ReactCommon/fabric/uimanager/TreeMutationInstruction.cpp

@@ -82,10 +82,8 @@ const TreeMutationInstruction TreeMutationInstruction::Replace(
   SharedShadowNode newChildNode,
   int index
 ) {
-  assert(parentNode);
   assert(oldChildNode);
   assert(newChildNode);
-  assert(index != -1);
 
   return TreeMutationInstruction(
     Replacement,