Set up infra for react-reconciler fork

packages/shared/ReactFeatureFlags.js

@@ -111,6 +111,8 @@ export const warnAboutSpreadingKeyToJSX = false;
 // Internal-only attempt to debug a React Native issue. See D20130868.
 export const throwEarlyForMysteriousError = false;
 
+export const enableNewReconciler = false;
+
 // --------------------------
 // Future APIs to be deprecated
 // --------------------------

packages/shared/forks/ReactFeatureFlags.native-fb.js

@@ -52,6 +52,8 @@ export const enableLegacyFBPrimerSupport = false;
 // Internal-only attempt to debug a React Native issue. See D20130868.
 export const throwEarlyForMysteriousError = true;
 
+export const enableNewReconciler = false;
+
 // Only used in www builds.
 export function addUserTimingListener() {
   invariant(false, 'Not implemented.');

packages/shared/forks/ReactFeatureFlags.native-oss.js

@@ -51,6 +51,8 @@ export const enableLegacyFBPrimerSupport = false;
 // Internal-only attempt to debug a React Native issue. See D20130868.
 export const throwEarlyForMysteriousError = false;
 
+export const enableNewReconciler = false;
+
 // Only used in www builds.
 export function addUserTimingListener() {
   invariant(false, 'Not implemented.');

packages/shared/forks/ReactFeatureFlags.test-renderer.js

@@ -51,6 +51,8 @@ export const enableLegacyFBPrimerSupport = false;
 // Internal-only attempt to debug a React Native issue. See D20130868.
 export const throwEarlyForMysteriousError = false;
 
+export const enableNewReconciler = false;
+
 // Only used in www builds.
 export function addUserTimingListener() {
   invariant(false, 'Not implemented.');

packages/shared/forks/ReactFeatureFlags.test-renderer.www.js

@@ -51,6 +51,8 @@ export const enableLegacyFBPrimerSupport = false;
 // Internal-only attempt to debug a React Native issue. See D20130868.
 export const throwEarlyForMysteriousError = false;
 
+export const enableNewReconciler = false;
+
 // Only used in www builds.
 export function addUserTimingListener() {
   invariant(false, 'Not implemented.');

packages/shared/forks/ReactFeatureFlags.testing.js

@@ -51,6 +51,8 @@ export const enableLegacyFBPrimerSupport = false;
 // Internal-only attempt to debug a React Native issue. See D20130868.
 export const throwEarlyForMysteriousError = false;
 
+export const enableNewReconciler = false;
+
 // Only used in www builds.
 export function addUserTimingListener() {
   invariant(false, 'Not implemented.');

packages/shared/forks/ReactFeatureFlags.testing.www.js

@@ -51,6 +51,8 @@ export const enableLegacyFBPrimerSupport = !__EXPERIMENTAL__;
 // Internal-only attempt to debug a React Native issue. See D20130868.
 export const throwEarlyForMysteriousError = false;
 
+export const enableNewReconciler = false;
+
 // Only used in www builds.
 export function addUserTimingListener() {
   invariant(false, 'Not implemented.');

packages/shared/forks/ReactFeatureFlags.www.js

@@ -109,6 +109,11 @@ export const enableLegacyFBPrimerSupport = !__EXPERIMENTAL__;
 // Internal-only attempt to debug a React Native issue. See D20130868.
 export const throwEarlyForMysteriousError = false;
 
+// Enable forked reconciler. Piggy-backing on the "variant" global so that we
+// don't have to add another test dimension. The build system will compile this
+// to the correct value.
+export const enableNewReconciler = __VARIANT__;
+
 // 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;

scripts/jest/setupHostConfigs.js

@@ -2,6 +2,15 @@
 
 const inlinedHostConfigs = require('../shared/inlinedHostConfigs');
 
+jest.mock('react-reconciler/src/ReactFiberReconciler', () => {
+  return require.requireActual(
+    __VARIANT__
+      ? // TODO: Update this to point to the new module, once it exists
+        'react-reconciler/src/ReactFiberReconciler.old'
+      : 'react-reconciler/src/ReactFiberReconciler.old'
+  );
+});
+
 // When testing the custom renderer code path through `react-reconciler`,
 // turn the export into a function, and use the argument as host config.
 const shimHostConfigPath = 'react-reconciler/src/ReactFiberHostConfig';

scripts/rollup/build.js

@@ -324,10 +324,11 @@ function getPlugins(
   bundleType,
   globalName,
   moduleType,
-  pureExternalModules
+  pureExternalModules,
+  bundle
 ) {
   const findAndRecordErrorCodes = extractErrorCodes(errorCodeOpts);
-  const forks = Modules.getForks(bundleType, entry, moduleType);
+  const forks = Modules.getForks(bundleType, entry, moduleType, bundle);
   const isProduction = isProductionBundleType(bundleType);
   const isProfiling = isProfilingBundleType(bundleType);
   const isUMDBundle =
@@ -391,7 +392,9 @@ function getPlugins(
       __UMD__: isUMDBundle ? 'true' : 'false',
       'process.env.NODE_ENV': isProduction ? "'production'" : "'development'",
       __EXPERIMENTAL__,
-      __VARIANT__: false,
+      // Enable forked reconciler.
+      // NOTE: I did not put much thought into how to configure this.
+      __VARIANT__: bundle.enableNewReconciler === true,
     }),
     // The CommonJS plugin *only* exists to pull "art" into "react-art".
     // I'm going to port "art" to ES modules to avoid this problem.
@@ -578,7 +581,8 @@ async function createBundle(bundle, bundleType) {
       bundleType,
       bundle.global,
       bundle.moduleType,
-      pureExternalModules
+      pureExternalModules,
+      bundle
     ),
     output: {
       externalLiveBindings: false,

scripts/rollup/bundles.js

@@ -95,6 +95,16 @@ const bundles = [
     externals: ['react'],
   },
 
+  /******* React DOM - www - Uses forked reconciler *******/
+  {
+    moduleType: RENDERER,
+    bundleTypes: [FB_WWW_DEV, FB_WWW_PROD, FB_WWW_PROFILING],
+    entry: 'react-dom',
+    global: 'ReactDOMForked',
+    enableNewReconciler: true,
+    externals: ['react'],
+  },
+
   /******* Test Utils *******/
   {
     moduleType: RENDERER_UTILS,

scripts/rollup/forks.js

@@ -246,6 +246,27 @@ const forks = Object.freeze({
     }
   },
 
+  'react-reconciler/src/ReactFiberReconciler': (
+    bundleType,
+    entry,
+    dependencies,
+    moduleType,
+    bundle
+  ) => {
+    if (bundle.enableNewReconciler) {
+      switch (bundleType) {
+        case FB_WWW_DEV:
+        case FB_WWW_PROD:
+        case FB_WWW_PROFILING:
+          // Use the forked version of the reconciler
+          // TODO: Update this to point to the new module, once it exists
+          return 'react-reconciler/src/ReactFiberReconciler.old.js';
+      }
+    }
+    // Otherwise, use the non-forked version.
+    return 'react-reconciler/src/ReactFiberReconciler.old.js';
+  },
+
   // Different dialogs for caught errors.
   'react-reconciler/src/ReactFiberErrorDialog': (bundleType, entry) => {
     switch (bundleType) {

scripts/rollup/modules.js

@@ -60,15 +60,16 @@ function getDependencies(bundleType, entry) {
 }
 
 // Hijacks some modules for optimization and integration reasons.
-function getForks(bundleType, entry, moduleType) {
+function getForks(bundleType, entry, moduleType, bundle) {
   const forksForBundle = {};
   Object.keys(forks).forEach(srcModule => {
     const dependencies = getDependencies(bundleType, entry);
     const targetModule = forks[srcModule](
       bundleType,
       entry,
       dependencies,
-      moduleType
+      moduleType,
+      bundle
     );
     if (targetModule === null) {
       return;