Fix dead code elimination for feature flags

.flowconfig

@@ -2,7 +2,15 @@
 
 <PROJECT_ROOT>/fixtures/.*
 <PROJECT_ROOT>/build/.*
-<PROJECT_ROOT>/scripts/.*
+<PROJECT_ROOT>/scripts/bench/.*
+
+# These shims are copied into external projects:
+<PROJECT_ROOT>/scripts/rollup/shims/facebook-www/.*
+<PROJECT_ROOT>/scripts/rollup/shims/react-native/.*
+
+# Note: intentionally *don't* ignore /scripts/rollup/shims/rollup/
+# because it is part of the build and isn't external.
+
 <PROJECT_ROOT>/.*/node_modules/y18n/.*
 <PROJECT_ROOT>/node_modules/chrome-devtools-frontend/.*
 <PROJECT_ROOT>/node_modules/devtools-timeline-model/.*

packages/react-cs-renderer/src/ReactNativeCSFeatureFlags.js

@@ -7,17 +7,21 @@
  * @flow
  */
 
-import type {FeatureFlags} from 'shared/ReactFeatureFlags';
+import typeof * as FeatureFlagsType from 'shared/ReactFeatureFlags';
+import typeof * as CSFeatureFlagsType from './ReactNativeCSFeatureFlags';
 
-var ReactNativeCSFeatureFlags: FeatureFlags = {
-  enableAsyncSubtreeAPI: true,
-  enableAsyncSchedulingByDefaultInReactDOM: false,
-  enableReactFragment: false,
-  enableCreateRoot: false,
-  // React Native CS uses persistent reconciler.
-  enableMutatingReconciler: false,
-  enableNoopReconciler: false,
-  enablePersistentReconciler: true,
-};
+export const enableAsyncSubtreeAPI = true;
+export const enableAsyncSchedulingByDefaultInReactDOM = false;
+export const enableReactFragment = false;
+export const enableCreateRoot = false;
 
-export default ReactNativeCSFeatureFlags;
+// React Native CS uses persistent reconciler.
+export const enableMutatingReconciler = false;
+export const enableNoopReconciler = false;
+export const enablePersistentReconciler = true;
+
+// Flow magic to verify the exports of this file match the original version.
+// eslint-disable-next-line no-unused-vars
+type Check<_X, Y: _X, X: Y=_X> = null;
+// eslint-disable-next-line no-unused-expressions
+(null: Check<CSFeatureFlagsType, FeatureFlagsType>);

packages/react-dom/src/client/ReactDOM.js

@@ -25,7 +25,10 @@ import * as EventPluginHub from 'events/EventPluginHub';
 import * as EventPluginRegistry from 'events/EventPluginRegistry';
 import * as EventPropagators from 'events/EventPropagators';
 import * as ReactInstanceMap from 'shared/ReactInstanceMap';
-import ReactFeatureFlags from 'shared/ReactFeatureFlags';
+import {
+  enableAsyncSchedulingByDefaultInReactDOM,
+  enableCreateRoot,
+} from 'shared/ReactFeatureFlags';
 import ReactVersion from 'shared/ReactVersion';
 import * as ReactDOMFrameScheduling from 'shared/ReactDOMFrameScheduling';
 import {ReactCurrentOwner} from 'shared/ReactGlobalSharedState';
@@ -633,7 +636,7 @@ var DOMRenderer = ReactFiberReconciler({
 
   scheduleDeferredCallback: ReactDOMFrameScheduling.rIC,
 
-  useSyncScheduling: !ReactFeatureFlags.enableAsyncSchedulingByDefaultInReactDOM,
+  useSyncScheduling: !enableAsyncSchedulingByDefaultInReactDOM,
 });
 
 ReactGenericBatching.injection.injectFiberBatchedUpdates(
@@ -945,7 +948,7 @@ var ReactDOM: Object = {
   },
 };
 
-if (ReactFeatureFlags.enableCreateRoot) {
+if (enableCreateRoot) {
   ReactDOM.createRoot = function createRoot(
     container: DOMContainer,
     options?: RootOptions,

packages/react-noop-renderer/src/ReactNoop.js

@@ -21,7 +21,7 @@ import type {UpdateQueue} from 'react-reconciler/src/ReactFiberUpdateQueue';
 import ReactFiberInstrumentation
   from 'react-reconciler/src/ReactFiberInstrumentation';
 import ReactFiberReconciler from 'react-reconciler';
-import ReactFeatureFlags from 'shared/ReactFeatureFlags';
+import {enablePersistentReconciler} from 'shared/ReactFeatureFlags';
 import * as ReactInstanceMap from 'shared/ReactInstanceMap';
 import emptyObject from 'fbjs/lib/emptyObject';
 import expect from 'expect';
@@ -213,7 +213,7 @@ var NoopRenderer = ReactFiberReconciler({
   },
 });
 
-var PersistentNoopRenderer = ReactFeatureFlags.enablePersistentReconciler
+var PersistentNoopRenderer = enablePersistentReconciler
   ? ReactFiberReconciler({
       ...SharedHostConfig,
       persistence: {

packages/react-reconciler/src/ReactChildFiber.js

@@ -14,7 +14,7 @@ import type {
   ExpirationTime,
 } from 'react-reconciler/src/ReactFiberExpirationTime';
 
-import ReactFeatureFlags from 'shared/ReactFeatureFlags';
+import {enableReactFragment} from 'shared/ReactFeatureFlags';
 import {NoEffect, Placement, Deletion} from 'shared/ReactTypeOfSideEffect';
 import {
   FunctionalComponent,
@@ -1426,7 +1426,7 @@ function ChildReconciler(shouldClone, shouldTrackSideEffects) {
     // This leads to an ambiguity between <>{[...]}</> and <>...</>.
     // We treat the ambiguous cases above the same.
     if (
-      ReactFeatureFlags.enableReactFragment &&
+      enableReactFragment &&
       typeof newChild === 'object' &&
       newChild !== null &&
       newChild.type === REACT_FRAGMENT_TYPE &&

packages/react-reconciler/src/ReactFiberClassComponent.js

@@ -11,7 +11,7 @@ import type {Fiber} from './ReactFiber';
 import type {ExpirationTime} from './ReactFiberExpirationTime';
 
 import {Update} from 'shared/ReactTypeOfSideEffect';
-import ReactFeatureFlags from 'shared/ReactFeatureFlags';
+import {enableAsyncSubtreeAPI} from 'shared/ReactFeatureFlags';
 import {isMounted} from 'shared/ReactFiberTreeReflection';
 import * as ReactInstanceMap from 'shared/ReactInstanceMap';
 import emptyObject from 'fbjs/lib/emptyObject';
@@ -450,7 +450,7 @@ export default function(
     instance.context = getMaskedContext(workInProgress, unmaskedContext);
 
     if (
-      ReactFeatureFlags.enableAsyncSubtreeAPI &&
+      enableAsyncSubtreeAPI &&
       workInProgress.type != null &&
       workInProgress.type.prototype != null &&
       workInProgress.type.prototype.unstable_isAsyncReactComponent === true

packages/react-reconciler/src/ReactFiberCommitWork.js

@@ -10,7 +10,11 @@
 import type {HostConfig} from 'react-reconciler';
 import type {Fiber} from './ReactFiber';
 
-import ReactFeatureFlags from 'shared/ReactFeatureFlags';
+import {
+  enableMutatingReconciler,
+  enableNoopReconciler,
+  enablePersistentReconciler,
+} from 'shared/ReactFeatureFlags';
 import {
   ClassComponent,
   HostRoot,
@@ -218,12 +222,9 @@ export default function<T, P, I, TI, PI, C, CC, CX, PL>(
         // TODO: this is recursive.
         // We are also not using this parent because
         // the portal will get pushed immediately.
-        if (ReactFeatureFlags.enableMutatingReconciler && mutation) {
+        if (enableMutatingReconciler && mutation) {
           unmountHostComponents(current);
-        } else if (
-          ReactFeatureFlags.enablePersistentReconciler &&
-          persistence
-        ) {
+        } else if (enablePersistentReconciler && persistence) {
           emptyPortalContainer(current);
         }
         return;
@@ -324,10 +325,7 @@ export default function<T, P, I, TI, PI, C, CC, CX, PL>(
         // Noop
       };
     }
-    if (
-      ReactFeatureFlags.enablePersistentReconciler ||
-      ReactFeatureFlags.enableNoopReconciler
-    ) {
+    if (enablePersistentReconciler || enableNoopReconciler) {
       return {
         commitResetTextContent(finishedWork: Fiber) {},
         commitPlacement(finishedWork: Fiber) {},
@@ -660,7 +658,7 @@ export default function<T, P, I, TI, PI, C, CC, CX, PL>(
     resetTextContent(current.stateNode);
   }
 
-  if (ReactFeatureFlags.enableMutatingReconciler) {
+  if (enableMutatingReconciler) {
     return {
       commitResetTextContent,
       commitPlacement,

packages/react-reconciler/src/ReactFiberCompleteWork.js

@@ -15,7 +15,11 @@ import type {HostContext} from './ReactFiberHostContext';
 import type {HydrationContext} from './ReactFiberHydrationContext';
 import type {FiberRoot} from './ReactFiberRoot';
 
-import ReactFeatureFlags from 'shared/ReactFeatureFlags';
+import {
+  enableMutatingReconciler,
+  enablePersistentReconciler,
+  enableNoopReconciler,
+} from 'shared/ReactFeatureFlags';
 import {
   IndeterminateComponent,
   FunctionalComponent,
@@ -180,7 +184,7 @@ export default function<T, P, I, TI, PI, C, CC, CX, PL>(
   let updateHostComponent;
   let updateHostText;
   if (mutation) {
-    if (ReactFeatureFlags.enableMutatingReconciler) {
+    if (enableMutatingReconciler) {
       // Mutation mode
       updateHostContainer = function(workInProgress: Fiber) {
         // Noop
@@ -217,7 +221,7 @@ export default function<T, P, I, TI, PI, C, CC, CX, PL>(
       invariant(false, 'Mutating reconciler is disabled.');
     }
   } else if (persistence) {
-    if (ReactFeatureFlags.enablePersistentReconciler) {
+    if (enablePersistentReconciler) {
       // Persistent host tree mode
       const {
         cloneInstance,
@@ -354,7 +358,7 @@ export default function<T, P, I, TI, PI, C, CC, CX, PL>(
       invariant(false, 'Persistent reconciler is disabled.');
     }
   } else {
-    if (ReactFeatureFlags.enableNoopReconciler) {
+    if (enableNoopReconciler) {
       // No host operations
       updateHostContainer = function(workInProgress: Fiber) {
         // Noop

packages/react-reconciler/src/ReactFiberReconciler.js

@@ -11,7 +11,7 @@ import type {Fiber} from './ReactFiber';
 import type {FiberRoot} from './ReactFiberRoot';
 import type {ReactNodeList} from 'shared/ReactTypes';
 
-import ReactFeatureFlags from 'shared/ReactFeatureFlags';
+import {enableAsyncSubtreeAPI} from 'shared/ReactFeatureFlags';
 import {
   findCurrentHostFiber,
   findCurrentHostFiberWithNoPortals,
@@ -303,7 +303,7 @@ export default function<T, P, I, TI, PI, C, CC, CX, PL>(
     // treat updates to the root as async. This is a bit weird but lets us
     // avoid a separate `renderAsync` API.
     if (
-      ReactFeatureFlags.enableAsyncSubtreeAPI &&
+      enableAsyncSubtreeAPI &&
       element != null &&
       element.type != null &&
       element.type.prototype != null &&

packages/react/src/React.js

@@ -7,7 +7,7 @@
 
 import assign from 'object-assign';
 import ReactVersion from 'shared/ReactVersion';
-import ReactFeatureFlags from 'shared/ReactFeatureFlags';
+import {enableReactFragment} from 'shared/ReactFeatureFlags';
 
 import {Component, PureComponent, AsyncComponent} from './ReactBaseClasses';
 import {forEach, map, count, toArray, only} from './ReactChildren';
@@ -58,7 +58,7 @@ var React = {
   },
 };
 
-if (ReactFeatureFlags.enableReactFragment) {
+if (enableReactFragment) {
   React.Fragment = REACT_FRAGMENT_TYPE;
 }
 

packages/shared/ReactFeatureFlags.js

@@ -7,35 +7,16 @@
  * @flow
  */
 
-export type FeatureFlags = {|
-  enableAsyncSubtreeAPI: boolean,
-  enableAsyncSchedulingByDefaultInReactDOM: boolean,
-  enableMutatingReconciler: boolean,
-  enableNoopReconciler: boolean,
-  enablePersistentReconciler: boolean,
-  enableReactFragment: boolean,
-  enableCreateRoot: boolean,
-|};
+export const enableAsyncSubtreeAPI = true;
+export const enableAsyncSchedulingByDefaultInReactDOM = false;
+// Exports React.Fragment
+export const enableReactFragment = false;
+// Exports ReactDOM.createRoot
+export const enableCreateRoot = false;
 
-var ReactFeatureFlags: FeatureFlags = {
-  enableAsyncSubtreeAPI: true,
-  enableAsyncSchedulingByDefaultInReactDOM: false,
-  // Mutating mode (React DOM, React ART, React Native):
-  enableMutatingReconciler: true,
-  // Experimental noop mode (currently unused):
-  enableNoopReconciler: false,
-  // Experimental persistent mode (CS):
-  enablePersistentReconciler: false,
-  // Exports React.Fragment
-  enableReactFragment: false,
-  // Exports ReactDOM.createRoot
-  enableCreateRoot: false,
-};
-
-if (__DEV__) {
-  if (Object.freeze) {
-    Object.freeze(ReactFeatureFlags);
-  }
-}
-
-export default ReactFeatureFlags;
+// Mutating mode (React DOM, React ART, React Native):
+export const enableMutatingReconciler = true;
+// Experimental noop mode (currently unused):
+export const enableNoopReconciler = false;
+// Experimental persistent mode (CS):
+export const enablePersistentReconciler = false;

scripts/flow/environment.js

@@ -12,3 +12,8 @@
 declare var __REACT_DEVTOOLS_GLOBAL_HOOK__: any; /*?{
   inject: ?((stuff: Object) => void)
 };*/
+
+// ReactFeatureFlags rollup shim for www imports the www implementation.
+declare module 'ReactFeatureFlags' {
+  declare module.exports: any;
+}

scripts/jest/setup.js

@@ -1,12 +1,9 @@
 'use strict';
 
-// We want to globally mock this but jest doesn't let us do that by default
-// for a file that already exists. So we have to explicitly mock it.
 jest.mock('shared/ReactFeatureFlags', () => {
-  const flags = require.requireActual('shared/ReactFeatureFlags').default;
-  return Object.assign({}, flags, {
-    disableNewFiberFeatures: true,
-  });
+  // We can alter flags based on environment here
+  // (e.g. for CI runs with different flags).
+  return require.requireActual('shared/ReactFeatureFlags');
 });
 
 // Error logging varies between Fiber and Stack;