From ff84c7360334792a9a422bd0fa0353e0cf670525 Mon Sep 17 00:00:00 2001
From: Andrew Scott <atscott@google.com>
Date: Mon, 28 Nov 2022 14:43:18 -0800
Subject: [PATCH] docs(core): Document invalid multi token (#48267)

Add error page for invalid multi token runtime error

PR Close #48267
---
 aio/content/errors/NG0209.md                    | 17 +++++++++++++++++
 goldens/public-api/core/errors.md               |  2 +-
 packages/core/src/application_init.ts           |  1 +
 packages/core/src/application_ref.ts            | 12 ++++++++++--
 packages/core/src/errors.ts                     |  2 +-
 .../acceptance/environment_injector_spec.ts     |  7 ++-----
 6 files changed, 32 insertions(+), 9 deletions(-)
 create mode 100644 aio/content/errors/NG0209.md

diff --git a/aio/content/errors/NG0209.md b/aio/content/errors/NG0209.md
new file mode 100644
index 00000000000..f9d2593fd56
--- /dev/null
+++ b/aio/content/errors/NG0209.md
@@ -0,0 +1,17 @@
+@name Invalid multi provider
+@category runtime
+@shortDescription Expected provider to be `multi: true` but did not get an Array
+
+@description
+
+The Angular runtime will throw this error when it injects a token intended to be used with `multi: true` but
+a non-Array was found instead. For example, `ENVIRONMENT_INITIALIZER` should be provided
+like `{provide: ENVIRONMENT_INITIALIZER, multi: true, useValue: () => {...}}`.
+
+<!-- links -->
+
+<!-- external links -->
+
+<!-- end links -->
+
+@reviewed 2022-11-28
\ No newline at end of file
diff --git a/goldens/public-api/core/errors.md b/goldens/public-api/core/errors.md
index 65712aab89c..be27a49c234 100644
--- a/goldens/public-api/core/errors.md
+++ b/goldens/public-api/core/errors.md
@@ -59,7 +59,7 @@ export const enum RuntimeErrorCode {
     // (undocumented)
     INVALID_INJECTION_TOKEN = 204,
     // (undocumented)
-    INVALID_MULTI_PROVIDER = 209,
+    INVALID_MULTI_PROVIDER = -209,
     // (undocumented)
     MISSING_GENERATED_DEF = 906,
     // (undocumented)
diff --git a/packages/core/src/application_init.ts b/packages/core/src/application_init.ts
index 418de8832f1..efa0a813594 100644
--- a/packages/core/src/application_init.ts
+++ b/packages/core/src/application_init.ts
@@ -102,6 +102,7 @@ export class ApplicationInitStatus {
 
   constructor(@Inject(APP_INITIALIZER) @Optional() private readonly appInits:
                   ReadonlyArray<() => Observable<unknown>| Promise<unknown>| void>) {
+    // TODO: Throw RuntimeErrorCode.INVALID_MULTI_PROVIDER if appInits is not an array
     this.donePromise = new Promise((res, rej) => {
       this.resolve = res;
       this.reject = rej;
diff --git a/packages/core/src/application_ref.ts b/packages/core/src/application_ref.ts
index a16e2107d5c..cc2009a7d0f 100644
--- a/packages/core/src/application_ref.ts
+++ b/packages/core/src/application_ref.ts
@@ -1051,8 +1051,16 @@ export class ApplicationRef {
     this.tick();
     this.components.push(componentRef);
     // Get the listeners lazily to prevent DI cycles.
-    const listeners =
-        this._injector.get(APP_BOOTSTRAP_LISTENER, []).concat(this._bootstrapListeners);
+    const listeners = this._injector.get(APP_BOOTSTRAP_LISTENER, []);
+    if (ngDevMode && !Array.isArray(listeners)) {
+      throw new RuntimeError(
+          RuntimeErrorCode.INVALID_MULTI_PROVIDER,
+          'Unexpected type of the `APP_BOOTSTRAP_LISTENER` token value ' +
+              `(expected an array, but got ${typeof listeners}). ` +
+              'Please check that the `APP_BOOTSTRAP_LISTENER` token is configured as a ' +
+              '`multi: true` provider.');
+    }
+    listeners.push(...this._bootstrapListeners);
     listeners.forEach((listener) => listener(componentRef));
   }
 
diff --git a/packages/core/src/errors.ts b/packages/core/src/errors.ts
index 00f9f77ac56..082fbce572c 100644
--- a/packages/core/src/errors.ts
+++ b/packages/core/src/errors.ts
@@ -32,7 +32,7 @@ export const enum RuntimeErrorCode {
   INJECTOR_ALREADY_DESTROYED = 205,
   PROVIDER_IN_WRONG_CONTEXT = 207,
   MISSING_INJECTION_TOKEN = 208,
-  INVALID_MULTI_PROVIDER = 209,
+  INVALID_MULTI_PROVIDER = -209,
 
   // Template Errors
   MULTIPLE_COMPONENTS_MATCH = -300,
diff --git a/packages/core/test/acceptance/environment_injector_spec.ts b/packages/core/test/acceptance/environment_injector_spec.ts
index 03ee4a23620..981bd3699a1 100644
--- a/packages/core/test/acceptance/environment_injector_spec.ts
+++ b/packages/core/test/acceptance/environment_injector_spec.ts
@@ -8,6 +8,7 @@
 
 import {Component, ComponentFactoryResolver, createEnvironmentInjector, ENVIRONMENT_INITIALIZER, EnvironmentInjector, inject, InjectFlags, InjectionToken, INJECTOR, Injector, NgModuleRef, ViewContainerRef} from '@angular/core';
 import {R3Injector} from '@angular/core/src/di/r3_injector';
+import {RuntimeError, RuntimeErrorCode} from '@angular/core/src/errors';
 import {TestBed} from '@angular/core/testing';
 
 describe('environment injector', () => {
@@ -117,11 +118,7 @@ describe('environment injector', () => {
       useValue: () => {},
     }];
     expect(() => createEnvironmentInjector(providers, parentEnvInjector))
-        .toThrowError(
-            'NG0209: Unexpected type of the `ENVIRONMENT_INITIALIZER` token value ' +
-            '(expected an array, but got function). ' +
-            'Please check that the `ENVIRONMENT_INITIALIZER` token is configured as ' +
-            'a `multi: true` provider.');
+        .toThrowMatching((e: RuntimeError) => e.code === RuntimeErrorCode.INVALID_MULTI_PROVIDER);
   });
 
   it('should adopt environment-scoped providers', () => {