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addon/@ember/test-waiters/waiter-manager.ts

@@ -1,15 +1,25 @@
+import { assert } from '@ember/debug';
 import { PendingWaiterState, Waiter, WaiterName } from './types';
 
 import Ember from 'ember';
 import { registerWaiter } from '@ember/test';
 
 type Indexable = Record<any, unknown>;
 
-// NOTE: We can't use symbols when we could have multiple copies of the addon
-//       in the dep tree. So for now, we can use this private string-based key
-//       that all copies of the `@ember/test-waiters` can use.
-const PRIVATE_GLOBAL_DATA_KEY =
-  '__#private_global_state_for_test_waiters__do_not_access_if_you_want_your_projects_to_keep_working__';
+assert(`Expected the 'Symbol' global to be available in this environment. Environments without support for 'Symbol' are not supported by '@ember/test-waiters'. See: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol`, typeof Symbol !== 'undefined');
+
+// All copies of `@ember/test-waiters must have this same key/symbol.
+// Once this `@ember/test-waiters` is released, folks will want to use 'overrides'
+// to pin it across their whole dep graph.
+//
+// In the v1 addon version of this library, the build time highlander code will ensure
+// that there is only one copy,
+// And with the v2 addon version of this library, that is where pinning is important,
+// because either:
+// - highlander code will run, and boot out the v2 addon copy
+// - v2 addon has precedence, and the min-version of test-waiters throughout the
+//   dep graph should not preceed the version which this symbol was introduced.
+const PRIVATE_GLOBAL_DATA_KEY = Symbol.for(`@ember/test-waiters' WAITERS`);
 
 // this ensures that if @ember/test-waiters exists in multiple places in the
 // build output we will still use a single map of waiters (there really should