Enable regenerator for Hermes dev mode transform profile (#52651)

Summary:
Pull Request resolved: #52651

Changelog: [Internal]

Last year the `hermes-canary` profile was used to enable certain apps to use Static Hermes by enabling regenerator because debugger support for generator wasn't finished yet. However, we actually could have just keyed off of `options.dev` and still kept using `hermes-stable`.

The `hermes-canary` profile is actually meant to be used to run experiments. We should free up this profile to return it to the original intended purpose.

This diff makes all hermes profiles' dev mode use regenerator. Existing SH apps using `hermes-canary` should be unaffected. And apps using Hermes will change to use regenerator in dev mode, but that should be ok.

Reviewed By: robhogan

Differential Revision: D78450695

fbshipit-source-id: eb6a87fbc1f0e08d490fd0d1baa3611248f95764

Author: dannysu

packages/react-native-babel-preset/src/configs/main.js

@@ -38,16 +38,21 @@ function isFirstParty(fileName) {
 // use `this.foo = bar` instead of `this.defineProperty('foo', ...)`
 const loose = true;
 
-// For Static Hermes testing (experimental), the hermes-canary transformProfile
-// is used to enable regenerator (and some related lowering passes) because SH
-// requires more Babel lowering than Hermes temporarily.
 const getPreset = (src, options) => {
   const transformProfile =
     (options && options.unstable_transformProfile) || 'default';
   const isHermesStable = transformProfile === 'hermes-stable';
   const isHermesCanary = transformProfile === 'hermes-canary';
   const isHermes = isHermesStable || isHermesCanary;
 
+  // We enable regenerator for !isHermes. Additionally, in dev mode we also
+  // enable regenerator for the time being because Static Hermes doesn't yet
+  // support debugging native generators. However, some apps have native
+  // generators in release mode because it has already yielded perf wins. The
+  // next release of Static Hermes will close this gap, so this won't be
+  // permanent.
+  const enableRegenerator = !isHermes || options.dev;
+
   const isNull = src == null;
   const hasClass = isNull || src.indexOf('class') !== -1;
 
@@ -111,8 +116,8 @@ const getPreset = (src, options) => {
     extraPlugins.push([
       require('@babel/plugin-transform-named-capturing-groups-regex'),
     ]);
-    // Needed for regenerator for hermes-canary
-    if (isHermesCanary) {
+    // Needed for regenerator
+    if (isHermes && enableRegenerator) {
       extraPlugins.push([
         require('@babel/plugin-transform-optional-catch-binding'),
       ]);
@@ -145,17 +150,15 @@ const getPreset = (src, options) => {
   ) {
     extraPlugins.push([require('@babel/plugin-transform-react-display-name')]);
   }
-  // Check !isHermesStable because this is needed for regenerator for
-  // hermes-canary
-  if (!isHermesStable && (isNull || src.indexOf('?.') !== -1)) {
+  // This is also needed for regenerator
+  if (enableRegenerator && (isNull || src.indexOf('?.') !== -1)) {
     extraPlugins.push([
       require('@babel/plugin-transform-optional-chaining'),
       {loose: true},
     ]);
   }
-  // Check !isHermesStable because this is needed for regenerator for
-  // hermes-canary
-  if (!isHermesStable && (isNull || src.indexOf('??') !== -1)) {
+  // This is also needed for regenerator
+  if (enableRegenerator && (isNull || src.indexOf('??') !== -1)) {
     extraPlugins.push([
       require('@babel/plugin-transform-nullish-coalescing-operator'),
       {loose: true},
@@ -183,7 +186,7 @@ const getPreset = (src, options) => {
     extraPlugins.push([require('@babel/plugin-transform-react-jsx-self')]);
   }
 
-  if (isHermesCanary) {
+  if (isHermes && enableRegenerator) {
     const hasForOf =
       isNull || (src.indexOf('for') !== -1 && src.indexOf('of') !== -1);
     if (hasForOf) {
@@ -203,11 +206,11 @@ const getPreset = (src, options) => {
       require('@babel/plugin-transform-runtime'),
       {
         helpers: true,
-        regenerator: !isHermesStable,
+        regenerator: enableRegenerator,
         ...(isVersion && {version: options.enableBabelRuntime}),
       },
     ]);
-  } else if (isHermesCanary) {
+  } else if (isHermes && enableRegenerator) {
     extraPlugins.push([require('@babel/plugin-transform-regenerator')]);
   }