Use getter instead of constant to provide access to FabricUIManager b…

…inding

Summary:
The `FabricUIManager` module was providing access to the global binding defined by Fabric, adding proper typing for it.

The problem about this module is that it only evaluated the global binding once (during module evaluation) and it cached the result. If this module happened to be loaded before the binding is defined, which can happen in apps using the legacy renderer and Fabric together, this modules caches an `undefined` value indefinitely.

This refactors the module as a getter function to make sure this lazy behavior is handled correctly in the callsites.

Changelog: [Internal]

Reviewed By: javache

Differential Revision: D44065186

fbshipit-source-id: 7c5cfe674605f03ecb8ca0dabc4c823e0013da6b

Libraries/LayoutAnimation/LayoutAnimation.js

@@ -17,6 +17,7 @@ import type {
   LayoutAnimationType,
 } from '../Renderer/shims/ReactNativeTypes';
 
+import {getFabricUIManager} from '../ReactNative/FabricUIManager';
 import ReactNativeFeatureFlags from '../ReactNative/ReactNativeFeatureFlags';
 import Platform from '../Utilities/Platform';
 
@@ -77,7 +78,7 @@ function configureNext(
 
   // In Fabric, LayoutAnimations are unconditionally enabled for Android, and
   // conditionally enabled on iOS (pending fully shipping; this is a temporary state).
-  const FabricUIManager: FabricUIManagerSpec = global?.nativeFabricUIManager;
+  const FabricUIManager = getFabricUIManager();
   if (FabricUIManager?.configureNextLayoutAnimation) {
     global?.nativeFabricUIManager?.configureNextLayoutAnimation(
       config,

Libraries/ReactNative/FabricUIManager.js

@@ -59,6 +59,9 @@ export type Spec = {|
   +findShadowNodeByTag_DEPRECATED: (reactTag: number) => ?Node,
 |};
 
-const FabricUIManager: ?Spec = global.nativeFabricUIManager;
-
-module.exports = FabricUIManager;
+// This is exposed as a getter because apps using the legacy renderer AND
+// Fabric can define the binding lazily. If we evaluated the global and cached
+// it in the module we might be caching an `undefined` value before it is set.
+export function getFabricUIManager(): ?Spec {
+  return global.nativeFabricUIManager;
+}

Libraries/ReactNative/UIManager.js

@@ -12,6 +12,9 @@ import type {RootTag} from '../Types/RootTagTypes';
 import type {Spec as FabricUIManagerSpec} from './FabricUIManager';
 import type {Spec} from './NativeUIManager';
 
+import {getFabricUIManager} from './FabricUIManager';
+import nullthrows from 'nullthrows';
+
 export interface UIManagerJSInterface extends Spec {
   +getViewManagerConfig: (viewManagerName: string) => Object;
   +hasViewManagerConfig: (viewManagerName: string) => boolean;
@@ -57,8 +60,7 @@ const UIManager = {
     ) => void,
   ): void {
     if (isFabricReactTag(reactTag)) {
-      const FabricUIManager: FabricUIManagerSpec =
-        global?.nativeFabricUIManager;
+      const FabricUIManager = nullthrows(getFabricUIManager());
       const shadowNode =
         FabricUIManager.findShadowNodeByTag_DEPRECATED(reactTag);
       if (shadowNode) {
@@ -84,8 +86,7 @@ const UIManager = {
     ) => void,
   ): void {
     if (isFabricReactTag(reactTag)) {
-      const FabricUIManager: FabricUIManagerSpec =
-        global?.nativeFabricUIManager;
+      const FabricUIManager = nullthrows(getFabricUIManager());
       const shadowNode =
         FabricUIManager.findShadowNodeByTag_DEPRECATED(reactTag);
       if (shadowNode) {
@@ -113,8 +114,7 @@ const UIManager = {
     ) => void,
   ): void {
     if (isFabricReactTag(reactTag)) {
-      const FabricUIManager: FabricUIManagerSpec =
-        global?.nativeFabricUIManager;
+      const FabricUIManager = nullthrows(getFabricUIManager());
       const shadowNode =
         FabricUIManager.findShadowNodeByTag_DEPRECATED(reactTag);
       const ancestorShadowNode =
@@ -155,8 +155,7 @@ const UIManager = {
       console.warn(
         'RCTUIManager.measureLayoutRelativeToParent method is deprecated and it will not be implemented in newer versions of RN (Fabric) - T47686450',
       );
-      const FabricUIManager: FabricUIManagerSpec =
-        global?.nativeFabricUIManager;
+      const FabricUIManager = nullthrows(getFabricUIManager());
       const shadowNode =
         FabricUIManager.findShadowNodeByTag_DEPRECATED(reactTag);
       if (shadowNode) {