Add experimental_useHermesParser option in preset-flow

packages/babel-preset-flow/package.json

@@ -29,7 +29,8 @@
   },
   "devDependencies": {
     "@babel/core": "workspace:^",
-    "@babel/helper-plugin-test-runner": "workspace:^"
+    "@babel/helper-plugin-test-runner": "workspace:^",
+    "babel-plugin-syntax-hermes-parser": "^0.19.1"
   },
   "homepage": "https://babel.dev/docs/en/next/babel-preset-flow",
   "bugs": "https://github.com/babel/babel/issues?utf8=%E2%9C%93&q=is%3Aissue+label%3A%22area%3A%20flow%22+is%3Aopen",

packages/babel-preset-flow/src/index.ts

@@ -12,22 +12,39 @@ export default declarePreset((api, opts) => {
     all,
     allowDeclareFields,
     ignoreExtensions = false,
+    experimental_useHermesParser: useHermesParser = false,
   } = normalizeOptions(opts);
 
-  const flowPlugin = [transformFlowStripTypes, { all, allowDeclareFields }];
+  const plugins: any[] = [
+    [transformFlowStripTypes, { all, allowDeclareFields }],
+  ];
+
+  if (useHermesParser) {
+    if (Number.parseInt(process.versions.node, 10) < 12) {
+      throw new Error(
+        "The Hermes parser is only supported in Node 12 and later.",
+      );
+    }
+    if (IS_STANDALONE) {
+      throw new Error(
+        "The Hermes parser is not supported in the @babel/standalone.",
+      );
+    }
+    plugins.unshift("babel-plugin-syntax-hermes-parser");
+  }
 
   // TODO: In Babel 7, ignoreExtensions is always true.
   // Allow setting it to false in the next minor.
   if (process.env.BABEL_8_BREAKING ? ignoreExtensions : true) {
-    return { plugins: [flowPlugin] };
+    return { plugins };
   }
 
   if (process.env.BABEL_8_BREAKING) {
     return {
       overrides: [
         {
           test: filename => filename == null || !/\.tsx?$/.test(filename),
-          plugins: [flowPlugin],
+          plugins,
         },
       ],
     };

packages/babel-preset-flow/src/normalize-options.ts

@@ -2,7 +2,7 @@ import { OptionValidator } from "@babel/helper-validator-option";
 const v = new OptionValidator("@babel/preset-flow");
 
 export default function normalizeOptions(options: any = {}) {
-  let { all, ignoreExtensions } = options;
+  let { all, ignoreExtensions, experimental_useHermesParser } = options;
   const { allowDeclareFields } = options;
 
   if (process.env.BABEL_8_BREAKING) {
@@ -13,19 +13,29 @@ export default function normalizeOptions(options: any = {}) {
     const TopLevelOptions = {
       all: "all",
       ignoreExtensions: "ignoreExtensions",
+      experimental_useHermesParser: "experimental_useHermesParser",
     };
     v.validateTopLevelOptions(options, TopLevelOptions);
     all = v.validateBooleanOption(TopLevelOptions.all, all);
     ignoreExtensions = v.validateBooleanOption(
       TopLevelOptions.ignoreExtensions,
       ignoreExtensions,
     );
-    return { all, ignoreExtensions };
+    experimental_useHermesParser = v.validateBooleanOption(
+      TopLevelOptions.experimental_useHermesParser,
+      experimental_useHermesParser,
+    );
+    return {
+      all,
+      ignoreExtensions,
+      experimental_useHermesParser,
+    };
   } else {
     return {
       all,
       allowDeclareFields,
       ignoreExtensions,
+      experimental_useHermesParser,
     };
   }
 }

packages/babel-preset-flow/test/fixtures/flow-parser/hermes/input.js

@@ -0,0 +1,4 @@
+// @flow
+
+type TypeofAnimal = Dog extends Animal ? 'animal' : 'unknown';
+function foo(a) {}

packages/babel-preset-flow/test/fixtures/flow-parser/hermes/options.json

@@ -0,0 +1,4 @@
+{
+  "presets": [["flow", { "experimental_useHermesParser": true }]],
+  "minNodeVersion": "12.0.0"
+}

packages/babel-preset-flow/test/fixtures/flow-parser/hermes/output.js

@@ -0,0 +1 @@
+function foo(a) {}

packages/babel-preset-flow/test/normalize-options.skip-bundled.js

@@ -30,6 +30,7 @@ describe("normalize options", () => {
       expect(normalizeOptions({})).toMatchInlineSnapshot(`
         Object {
           "all": undefined,
+          "experimental_useHermesParser": undefined,
           "ignoreExtensions": undefined,
         }
       `);
@@ -50,6 +51,7 @@ describe("normalize options", () => {
         Object {
           "all": undefined,
           "allowDeclareFields": undefined,
+          "experimental_useHermesParser": undefined,
           "ignoreExtensions": undefined,
         }
       `);

yarn.lock

@@ -4007,6 +4007,7 @@ __metadata:
     "@babel/helper-plugin-utils": "workspace:^"
     "@babel/helper-validator-option": "workspace:^"
     "@babel/plugin-transform-flow-strip-types": "workspace:^"
+    babel-plugin-syntax-hermes-parser: "npm:^0.19.1"
   peerDependencies:
     "@babel/core": ^7.0.0-0
   languageName: unknown
@@ -6883,6 +6884,15 @@ __metadata:
   languageName: node
   linkType: hard
 
+"babel-plugin-syntax-hermes-parser@npm:^0.19.1":
+  version: 0.19.1
+  resolution: "babel-plugin-syntax-hermes-parser@npm:0.19.1"
+  dependencies:
+    hermes-parser: "npm:0.19.1"
+  checksum: cb99e79b2d979cd3a69be3da23748f957d9fab294464f0720602271afb1f4ec40bed71d8884549edf00fa47523c60e9ff2407f4a2a0167eb9ac1dd094c0f8b57
+  languageName: node
+  linkType: hard
+
 "babel-plugin-transform-charcodes@npm:^0.2.0":
   version: 0.2.0
   resolution: "babel-plugin-transform-charcodes@npm:0.2.0"
@@ -10638,6 +10648,22 @@ __metadata:
   languageName: node
   linkType: hard
 
+"hermes-estree@npm:0.19.1":
+  version: 0.19.1
+  resolution: "hermes-estree@npm:0.19.1"
+  checksum: dadafea5cf8fcf7d2c2d3d43740898c73b03db4747d4cc83e3cdb06bfcfbf3ee97f4ee26f077aea455771703f5bd18a4cb40c1ce7af9e38ce541d6c03fc8847a
+  languageName: node
+  linkType: hard
+
+"hermes-parser@npm:0.19.1":
+  version: 0.19.1
+  resolution: "hermes-parser@npm:0.19.1"
+  dependencies:
+    hermes-estree: "npm:0.19.1"
+  checksum: 4fd886ce3ab80c79b258fa60085f2915f587aef57bf59e17f6cfe3b0ad2e7b1a1cfff8371b736392f66cff0658a90ece279b608edcb5589f8c56957e799c56f2
+  languageName: node
+  linkType: hard
+
 "hmac-drbg@npm:^1.0.1":
   version: 1.0.1
   resolution: "hmac-drbg@npm:1.0.1"