Allow injecting looser VirtualizedList

Summary:
VirtualizedList_EXPERIMENTAL has a different flow signature from VirtualizedList. This does not cause an error in unit tests, which are untyped, but prevents injecting VirtualizedList_EXPERIMENTAL via the current API from flowtype. This diff updates the injection interface to allow a more relaxed type, validating safety at runtime.

Changelog:
[Internal][Changed] - Allow injecting looser VirtualizedList

Reviewed By: javache

Differential Revision: D38143682

fbshipit-source-id: 054bbc5092823f4e4413d69d3d72a7ecdd71a6a2

Libraries/Lists/VirtualizedList.js

@@ -28,6 +28,7 @@ import {
   computeWindowedRenderLimits,
   keyExtractor as defaultKeyExtractor,
 } from './VirtualizeUtils';
+import * as VirtualizedListInjection from './VirtualizedListInjection';
 import * as React from 'react';
 
 const RefreshControl = require('../Components/RefreshControl/RefreshControl');
@@ -302,7 +303,7 @@ type OptionalProps = {|
   legacyImplementation?: empty,
 |};
 
-type Props = {|
+export type Props = {|
   ...React.ElementConfig<typeof ScrollView>,
   ...RequiredProps,
   ...OptionalProps,
@@ -2217,5 +2218,6 @@ const styles = StyleSheet.create({
   },
 });
 
-module.exports = (require('./VirtualizedListInjection').default
-  .unstable_VirtualizedList ?? VirtualizedList: typeof VirtualizedList);
+module.exports = (VirtualizedListInjection.getOrDefault(
+  VirtualizedList,
+): typeof VirtualizedList);

Libraries/Lists/VirtualizedListInjection.js

@@ -4,13 +4,69 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict-local
  * @format
  */
 
 'use strict';
-import typeof VirtualizedList from './VirtualizedList';
 
-export default {
-  unstable_VirtualizedList: (null: ?VirtualizedList),
-};
+import * as React from 'react';
+import type VirtualizedList from './VirtualizedList';
+import type {Props as VirtualizedListProps} from './VirtualizedList';
+import invariant from 'invariant';
+
+export type ListImplementation = React.ComponentType<VirtualizedListProps> &
+  interface {};
+
+/**
+ * Global override to the VirtualizedList implementation used when imported
+ */
+let injection: ?ListImplementation;
+let retrieved = false;
+
+export function inject(listImplementation: ListImplementation): void {
+  invariant(
+    !retrieved,
+    'VirtualizedListInjection.inject() called after the injection was already retrieved',
+  );
+  injection = listImplementation;
+}
+
+export function getOrDefault(
+  defaultImplementation: Class<VirtualizedList>,
+): Class<VirtualizedList> {
+  retrieved = true;
+  return injection
+    ? verifyVirtualizedList(injection, defaultImplementation)
+    : defaultImplementation;
+}
+
+function verifyVirtualizedList(
+  injectedImplementation: ListImplementation,
+  defaultImplementation: Class<VirtualizedList>,
+): Class<VirtualizedList> {
+  // The original VirtualizedList marks method as "private by convention" by
+  // prefixing with underscore. These methods may still be called at runtime
+  // by tests or other internals, so they cannot be truly private, and will be
+  // included in the Flow type of VirtualizedList.
+  // Allow the injection to have different private methods by allowing a loose
+  // Flow type, but check at runtime that the set of public properties matches.
+  if (__DEV__) {
+    for (const field of Object.keys(defaultImplementation)) {
+      if (isPublicField(field)) {
+        invariant(
+          injectedImplementation.hasOwnProperty(field),
+          `VirtualizedList injection missing field: "${field}"`,
+        );
+      }
+    }
+  }
+
+  // $FlowExpectedError
+  return injectedImplementation;
+}
+
+function isPublicField(fieldName: string): boolean {
+  // Respect JSTransform public methods by double underscore (D33982339)
+  return fieldName.length > 0 && (fieldName[0] !== '_' || fieldName[1] === '_');
+}

Libraries/Lists/VirtualizedList_EXPERIMENTAL.js

@@ -307,7 +307,7 @@ type OptionalProps = {|
   legacyImplementation?: empty,
 |};
 
-type Props = {|
+export type Props = {|
   ...React.ElementConfig<typeof ScrollView>,
   ...RequiredProps,
   ...OptionalProps,

Libraries/Lists/__tests__/VirtualizedList-test.js

@@ -12,15 +12,14 @@
 
 import React from 'react';
 import ReactTestRenderer from 'react-test-renderer';
-import VirtualizedListInjection from '../VirtualizedListInjection';
+import * as VirtualizedListInjection from '../VirtualizedListInjection';
 import VirtualizedList_EXPERIMENTAL from '../VirtualizedList_EXPERIMENTAL';
 
 const useExperimentalList =
   process.env.USE_EXPERIMENTAL_VIRTUALIZEDLIST === 'true';
 
 if (useExperimentalList) {
-  VirtualizedListInjection.unstable_VirtualizedList =
-    VirtualizedList_EXPERIMENTAL;
+  VirtualizedListInjection.inject(VirtualizedList_EXPERIMENTAL);
 }
 
 const VirtualizedList = require('../VirtualizedList');