Make "process.env" case insensitive in Windows (#5465)

packages/jest-util/src/__tests__/create_process_object.test.js

@@ -30,3 +30,47 @@ it('creates a process object that looks like the original one', () => {
 it('fakes require("process") so it is equal to "global.process"', () => {
   expect(require('process') === process).toBe(true);
 });
+
+it('checks that process.env works as expected on Linux platforms', () => {
+  Object.defineProperty(process, 'platform', {get: () => 'linux'});
+
+  // Existing properties inside process.env are copied to the fake environment.
+  process.env.PROP_STRING = 'foo';
+  process.env.PROP_NUMBER = 3;
+  process.env.PROP_UNDEFINED = undefined;
+
+  const fake = createProcessObject().env;
+
+  // All values converted to strings.
+  expect(fake.PROP_STRING).toBe('foo');
+  expect(fake.PROP_NUMBER).toBe('3');
+  expect(fake.PROP_UNDEFINED).toBe('undefined');
+
+  // Mac and Linux are case sensitive.
+  expect(fake.PROP_string).toBe(undefined);
+
+  // Added properties to the fake object are not added to the real one.
+  fake.PROP_ADDED = 'new!';
+
+  expect(fake.PROP_ADDED).toBe('new!');
+  expect(process.env.PROP_ADDED).toBe(undefined);
+});
+
+it('checks that process.env works as expected in Windows platforms', () => {
+  Object.defineProperty(process, 'platform', {get: () => 'win32'});
+
+  // Windows is not case sensitive when it comes to property names.
+  process.env.PROP_STRING = 'foo';
+
+  const fake = createProcessObject().env;
+
+  expect(fake.PROP_STRING).toBe('foo');
+  expect(fake.PROP_string).toBe('foo');
+
+  // Inherited methods, however, are not affected by case insensitiveness.
+  expect(typeof fake.toString).toBe('function');
+  expect(typeof fake.valueOf).toBe('function');
+
+  expect(typeof fake.tostring).toBe('undefined');
+  expect(typeof fake.valueof).toBe('undefined');
+});

packages/jest-util/src/create_process_object.js

@@ -9,7 +9,43 @@
 
 import deepCyclicCopy from './deep_cyclic_copy';
 
-const BLACKLIST = new Set(['mainModule', '_events']);
+const BLACKLIST = new Set(['env', 'mainModule', '_events']);
+
+// The "process.env" object has a bunch of particularities: first, it does not
+// directly extend from Object; second, it converts any assigned value to a
+// string; and third, it is case-insensitive in Windows. We use a proxy here to
+// mimic it (see https://nodejs.org/api/process.html#process_process_env).
+
+function createProcessEnv() {
+  // $FlowFixMe: Apparently Flow does not understand that this is a prototype.
+  const proto: Object = Object.getPrototypeOf(process.env);
+  const real = Object.create(proto);
+  const lookup = {};
+
+  const proxy = new Proxy(real, {
+    get(target, key) {
+      if ((typeof key === 'string') && (process.platform === 'win32')) {
+        return lookup[key in proto ? key : key.toLowerCase()];
+      } else {
+        return real[key];
+      }
+    },
+
+    set(target, key, value) {
+      const strValue = '' + value;
+
+      if (typeof key === 'string') {
+        lookup[key.toLowerCase()] = strValue;
+      }
+
+      real[key] = strValue;
+
+      return true;
+    },
+  });
+
+  return Object.assign(proxy, process.env);
+}
 
 export default function() {
   const process = require('process');
@@ -29,5 +65,7 @@ export default function() {
     }
   }
 
+  newProcess.env = createProcessEnv();
+
   return newProcess;
 }