Fully remove weak and check only in runtime (#5252)

Author: mjesun

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### Fixes
 
+* `[jest-leak-detector]` Removed the reference to `weak`. Now, parent projects
+  must install it by hand for the module to work.
 * `[expect]` Fail test when the types of `stringContaining` and `stringMatching`
   matchers do not match. ([#5069](https://github.com/facebook/jest/pull/5069))
 * `[jest-cli]` Treat dumb terminals as noninteractive

packages/jest-leak-detector/package.json

@@ -10,7 +10,7 @@
   "dependencies": {
     "pretty-format": "^22.0.3"
   },
-  "optionalDependencies": {
+  "devDependencies": {
     "weak": "^1.0.1"
   }
 }

packages/jest-leak-detector/src/index.js

@@ -37,15 +37,16 @@ export default class {
     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 work. ' +
-          'Please make sure that you can install the native dependency on your platform.',
+        'The leaking detection mechanism requires the "weak" package to be installed and work. ' +
+          'Please install it as a dependency on your main project',
       );
     }