Migrate jest-leak-detector to TypeScript

[r3nya]

Summary

Hello! It my first PR, if I do something wrong, please let me know. 😉

Diff

diff --git a/packages/jest-leak-detector/build/index.js b/packages/jest-leak-detector/build/index.js
index 5402915b8..ff851b3fb 100644
--- a/packages/jest-leak-detector/build/index.js
+++ b/packages/jest-leak-detector/build/index.js
@@ -1,11 +1,3 @@
-/**
- * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- *
- *
- */
 'use strict';
 
 Object.defineProperty(exports, '__esModule', {
@@ -13,30 +5,30 @@ Object.defineProperty(exports, '__esModule', {
 });
 exports.default = void 0;
 
-function _prettyFormat() {
-  const data = _interopRequireDefault(require('pretty-format'));
+function _v() {
+  const data = _interopRequireDefault(require('v8'));
 
-  _prettyFormat = function _prettyFormat() {
+  _v = function _v() {
     return data;
   };
 
   return data;
 }
 
-function _v() {
-  const data = _interopRequireDefault(require('v8'));
+function _vm() {
+  const data = _interopRequireDefault(require('vm'));
 
-  _v = function _v() {
+  _vm = function _vm() {
     return data;
   };
 
   return data;
 }
 
-function _vm() {
-  const data = _interopRequireDefault(require('vm'));
+function _prettyFormat() {
+  const data = _interopRequireDefault(require('pretty-format'));
 
-  _vm = function _vm() {
+  _prettyFormat = function _prettyFormat() {
     return data;
   };
 
@@ -47,6 +39,12 @@ function _interopRequireDefault(obj) {
   return obj && obj.__esModule ? obj : {default: obj};
 }
 
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
 class _default {
   constructor(value) {
     if (this._isPrimitive(value)) {
diff --git a/packages/jest-leak-detector/build/index.ts_ b/packages/jest-leak-detector/build/index.ts_
new file mode 100644
index 000000000..c5ad07ba7
--- /dev/null
+++ b/packages/jest-leak-detector/build/index.ts_
@@ -0,0 +1,72 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+'use strict';
+
+import prettyFormat from 'pretty-format';
+import v8 from 'v8';
+import vm from 'vm';
+
+export default class {
+  _isReferenceBeingHeld: boolean;
+
+  constructor(value: ?Object) {
+    if (this._isPrimitive(value)) {
+      throw new TypeError(
+        [
+          'Primitives cannot leak memory.',
+          'You passed a ' + typeof value + ': <' + prettyFormat(value) + '>',
+        ].join(' '),
+      );
+    }
+
+    let weak;
+
+    try {
+      // eslint-disable-next-line import/no-extraneous-dependencies
+      weak = require('weak');
+    } catch (err) {
+      if (!err || err.code !== 'MODULE_NOT_FOUND') {
+        throw err;
+      }
+
+      throw new Error(
+        'The leaking detection mechanism requires the "weak" package to be installed and work. ' +
+          'Please install it as a dependency on your main project',
+      );
+    }
+
+    weak(value, () => (this._isReferenceBeingHeld = false));
+    this._isReferenceBeingHeld = true;
+
+    // Ensure value is not leaked by the closure created by the "weak" callback.
+    value = null;
+  }
+
+  isLeaking(): boolean {
+    this._runGarbageCollector();
+
+    return this._isReferenceBeingHeld;
+  }
+
+  _runGarbageCollector() {
+    const isGarbageCollectorHidden = !global.gc;
+
+    // GC is usually hidden, so we have to expose it before running.
+    v8.setFlagsFromString('--expose-gc');
+    vm.runInNewContext('gc')();
+
+    // The GC was not initially exposed, so let's hide it again.
+    if (isGarbageCollectorHidden) {
+      v8.setFlagsFromString('--no-expose-gc');
+    }
+  }
+
+  _isPrimitive(value: any): boolean {
+    return value !== Object(value);
+  }
+}

Test plan

💚 build;

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[SimenB]

Thanks!

Couple of things:

• The diff should be against the build on master. The point is to inspect the difference in the transpiled code so we can be sure there's no breaking change
• Don't push the commit with build artifacts - it's just for inspection before we merge 🙂

[facebook-github-bot]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Facebook open source project. Thanks!

[SimenB]

If CI is happy, this should be good to go 🙂

[r3nya]

@SimenB @thymikee thanks a lot for your help guys! 💚 CI now.

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