From e7c1cf5b7d2eba9468804635d0c2a0fc6725e42a Mon Sep 17 00:00:00 2001
From: Miguel Jimenez Esun <mjimenez@fb.com>
Date: Mon, 3 Jul 2017 09:51:28 -0700
Subject: [PATCH] Add a new babel transformer for inlining regenerator-runtime
 per file

Reviewed By: davidaurelio

Differential Revision: D5364134

fbshipit-source-id: 45aae705f961819d5a8e3a8a23c2e8b9300d3cb5
---
 babel-preset/configs/main.js                  |   1 +
 ...transform-regenerator-runtime-insertion.js | 109 ++++++++++++++++++
 package.json                                  |   1 +
 3 files changed, 111 insertions(+)
 create mode 100644 babel-preset/transforms/transform-regenerator-runtime-insertion.js

diff --git a/babel-preset/configs/main.js b/babel-preset/configs/main.js
index 5afbc9061a81c0..eb814e6ebdad6e 100644
--- a/babel-preset/configs/main.js
+++ b/babel-preset/configs/main.js
@@ -38,6 +38,7 @@ var base = {
     'transform-react-jsx',
     'transform-regenerator',
     ['transform-es2015-for-of', { loose: true }],
+    require('../transforms/transform-regenerator-runtime-insertion'),
     require('../transforms/transform-symbol-member'),
   ]),
 };
diff --git a/babel-preset/transforms/transform-regenerator-runtime-insertion.js b/babel-preset/transforms/transform-regenerator-runtime-insertion.js
new file mode 100644
index 00000000000000..a8d66181481a70
--- /dev/null
+++ b/babel-preset/transforms/transform-regenerator-runtime-insertion.js
@@ -0,0 +1,109 @@
+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ */
+
+'use strict';
+
+const babel = require('babel-core');
+const t = babel.types;
+
+const NAME = 'regenerator-runtime';
+const REGENERATOR_NOT_NEEDED = 'NOT_NEEDED';
+const REGENERATOR_NEEDED = 'NEEDED';
+const REGENERATOR_ALREADY_REQUIRED = 'ALREADY_REQUIRED';
+
+function flagState(state) {
+  if (state !== REGENERATOR_ALREADY_REQUIRED) {
+    state.regeneratorRequired = REGENERATOR_NEEDED;
+  }
+}
+
+function checkRequire(node, state) {
+  const method = node.callee.name;
+  const args = node.arguments;
+
+  if (
+    method === 'require' &&
+    t.isStringLiteral(args[0]) &&
+    args[0].value.startsWith(NAME)
+  ) {
+    state.regeneratorRequired = REGENERATOR_ALREADY_REQUIRED;
+  }
+}
+
+function checkFunction(node, state) {
+  // Method is neither a generator nor an async function; skip.
+  if (!node.generator && !node.async) {
+    return;
+  }
+
+  // This will only set the status to needed if it hasn't already been required.
+  if (state.regeneratorRequired === REGENERATOR_NOT_NEEDED) {
+    state.regeneratorRequired = REGENERATOR_NEEDED;
+  }
+}
+
+const isGeneratorRequired = {
+  CallExpression(path, state) {
+    checkRequire(path.node, state);
+  },
+
+  FunctionDeclaration(path, state) {
+    checkFunction(path.node, state);
+  },
+
+  ClassMethod(path, state) {
+    checkFunction(path.node, state);
+  },
+
+  ArrowFunctionExpression(path, state) {
+    checkFunction(path.node, state);
+  },
+
+  FunctionExpression(path, state) {
+    checkFunction(path.node, state);
+  },
+
+  YieldExpression(path, state) {
+    flagState(state);
+  },
+
+  AwaitExpression(path, state) {
+    flagState(state);
+  },
+};
+
+/**
+ * Adds a "const regeneratorRuntime = require('regenerator-runtime') to each
+ * file that does not include regenerator-runtime, but requires it because it
+ * contains async/await or generators.
+ */
+module.exports = function() {
+  return {
+    visitor: {
+      Program(path, state) {
+        state.regeneratorRequired = REGENERATOR_NOT_NEEDED;
+        path.traverse(isGeneratorRequired, state);
+
+        if (state.regeneratorRequired === REGENERATOR_NEEDED) {
+          path.node.body.unshift(
+            t.variableDeclaration('const', [
+              t.variableDeclarator(
+                t.identifier('regeneratorRuntime'),
+                t.callExpression(t.identifier('require'), [
+                  t.stringLiteral(NAME),
+                ])
+              )
+            ])
+          );
+        }
+      },
+    },
+  };
+};
diff --git a/package.json b/package.json
index b27cee68cd9515..e29513f4e01cfd 100644
--- a/package.json
+++ b/package.json
@@ -74,6 +74,7 @@
     ],
     "unmockedModulePathPatterns": [
       "node_modules/react/",
+      "node_modules/regenerator-runtime/",
       "Libraries/Renderer",
       "promise",
       "source-map",