Implement getBoundingClientRect in React Native

Summary:
We already have `getBoundingClientRect` implemented in Fabric, so we can expose this as a proper method in `ReactNativeElement` (behind a feature flag).

Changelog: [internal]

bypass-github-export-checks

Reviewed By: javache

Differential Revision: D44065187

fbshipit-source-id: bd87e72f78d135079f5440b0b0bd4c572b05ba2a

packages/react-native/Libraries/DOM/Nodes/ReadOnlyElement.js

@@ -12,8 +12,11 @@
 
 import type HTMLCollection from '../OldStyleCollections/HTMLCollection';
 
+import {getFabricUIManager} from '../../ReactNative/FabricUIManager';
+import DOMRect from '../Geometry/DOMRect';
 import {createHTMLCollection} from '../OldStyleCollections/HTMLCollection';
-import ReadOnlyNode, {getChildNodes} from './ReadOnlyNode';
+import ReadOnlyNode, {getChildNodes, getShadowNode} from './ReadOnlyNode';
+import nullthrows from 'nullthrows';
 
 export default class ReadOnlyElement extends ReadOnlyNode {
   get childElementCount(): number {
@@ -124,6 +127,23 @@ export default class ReadOnlyElement extends ReadOnlyNode {
     throw new TypeError('Unimplemented');
   }
 
+  getBoundingClientRect(): DOMRect {
+    const shadowNode = getShadowNode(this);
+
+    if (shadowNode != null) {
+      const rect = nullthrows(getFabricUIManager()).getBoundingClientRect(
+        shadowNode,
+      );
+
+      if (rect) {
+        return new DOMRect(rect[0], rect[1], rect[2], rect[3]);
+      }
+    }
+
+    // Empty rect if any of the above failed
+    return new DOMRect(0, 0, 0, 0);
+  }
+
   getClientRects(): DOMRectList {
     throw new TypeError('Unimplemented');
   }

packages/react-native/Libraries/DOM/Nodes/ReadOnlyNode.js

@@ -76,7 +76,7 @@ export default class ReadOnlyNode {
    */
   get nodeName(): string {
     throw new TypeError(
-      'Unexpected access to `nodeName` in abstract class `ReadOnlyNode`',
+      '`nodeName` is abstract and must be implemented in a subclass of `ReadOnlyNode`',
     );
   }
 

packages/react-native/Libraries/ReactNative/FabricUIManager.js

@@ -58,7 +58,7 @@ export type Spec = {|
   +findShadowNodeByTag_DEPRECATED: (reactTag: number) => ?Node,
   +getBoundingClientRect: (
     node: Node,
-  ) => [
+  ) => ?[
     /* x:*/ number,
     /* y:*/ number,
     /* width:*/ number,

packages/react-native/Libraries/ReactNative/__mocks__/FabricUIManager.js

@@ -113,6 +113,17 @@ function getAncestors(root: Node, node: Node): ?$ReadOnlyArray<[Node, number]> {
   return null;
 }
 
+function getNodeInCurrentTree(node: Node): ?Node {
+  const ancestors = getAncestorsInCurrentTree(node);
+  if (ancestors == null) {
+    return null;
+  }
+
+  const [parent, position] = ancestors[ancestors.length - 1];
+  const nodeInCurrentTree = fromNode(parent).children[position];
+  return nodeInCurrentTree;
+}
+
 const FabricUIManagerMock: FabricUIManager = {
   createNode: jest.fn(
     (
@@ -215,7 +226,7 @@ const FabricUIManagerMock: FabricUIManager = {
   getBoundingClientRect: jest.fn(
     (
       node: Node,
-    ): [
+    ): ?[
       /* x:*/ number,
       /* y:*/ number,
       /* width:*/ number,
@@ -223,7 +234,28 @@ const FabricUIManagerMock: FabricUIManager = {
     ] => {
       ensureHostNode(node);
 
-      return [10, 10, 100, 100];
+      const nodeInCurrentTree = getNodeInCurrentTree(node);
+      const currentProps =
+        nodeInCurrentTree != null ? fromNode(nodeInCurrentTree).props : null;
+      if (currentProps == null) {
+        return null;
+      }
+
+      const boundingClientRectForTests: ?{
+        x: number,
+        y: number,
+        width: number,
+        height: number,
+      } =
+        // $FlowExpectedError[prop-missing]
+        currentProps.__boundingClientRectForTests;
+
+      if (boundingClientRectForTests == null) {
+        return null;
+      }
+
+      const {x, y, width, height} = boundingClientRectForTests;
+      return [x, y, width, height];
     },
   ),
   setNativeProps: jest.fn((node: Node, newProps: NodeProps): void => {}),
@@ -242,13 +274,12 @@ const FabricUIManagerMock: FabricUIManager = {
   }),
   getChildNodes: jest.fn(
     (node: Node): $ReadOnlyArray<InternalInstanceHandle> => {
-      const ancestors = getAncestorsInCurrentTree(node);
-      if (ancestors == null) {
+      const nodeInCurrentTree = getNodeInCurrentTree(node);
+
+      if (nodeInCurrentTree == null) {
         return [];
       }
 
-      const [parent, position] = ancestors[ancestors.length - 1];
-      const nodeInCurrentTree = fromNode(parent).children[position];
       return fromNode(nodeInCurrentTree).children.map(
         child => fromNode(child).instanceHandle,
       );

packages/react-native/ReactCommon/react/renderer/uimanager/UIManagerBinding.cpp

@@ -728,10 +728,20 @@ jsi::Value UIManagerBinding::get(
    */
 
   if (methodName == "getBoundingClientRect") {
+    // This is a React Native implementation of
+    // `Element.prototype.getBoundingClientRect` (see
+    // https://developer.mozilla.org/en-US/docs/Web/API/Element/getBoundingClientRect).
+
     // This is similar to `measureInWindow`, except it's explicitly synchronous
     // (returns the result instead of passing it to a callback).
-    // The behavior is similar to `Element.prototype.getBoundingClientRect` from
-    // Web.
+
+    // getBoundingClientRect(shadowNode: ShadowNode):
+    //   [
+    //     /* x: */ number,
+    //     /* y: */ number,
+    //     /* width: */ number,
+    //     /* height: */ number
+    //   ]
     return jsi::Function::createFromHostFunction(
         runtime,
         name,