refactor(core): improve an error message when ENVIRONMENT_INITIALIZER is not a multi provider (#46829)

Currently if the `ENVIRONMENT_INITIALIZER` token is not configured with `multi: true` flag, the code fails while trying to iterate over the value. This commit checks whether the `ENVIRONMENT_INITIALIZER` token value type is an array and throws a helpful error message.

PR Close #46829

goldens/public-api/core/errors.md

@@ -47,6 +47,8 @@ export const enum RuntimeErrorCode {
     // (undocumented)
     INVALID_INJECTION_TOKEN = 204,
     // (undocumented)
+    INVALID_MULTI_PROVIDER = 209,
+    // (undocumented)
     MISSING_GENERATED_DEF = 906,
     // (undocumented)
     MISSING_INJECTION_CONTEXT = -203,

packages/core/src/di/r3_injector.ts

@@ -272,6 +272,14 @@ export class R3Injector extends EnvironmentInjector {
     const previousInjectImplementation = setInjectImplementation(undefined);
     try {
       const initializers = this.get(ENVIRONMENT_INITIALIZER.multi, EMPTY_ARRAY, InjectFlags.Self);
+      if (ngDevMode && !Array.isArray(initializers)) {
+        throw new RuntimeError(
+            RuntimeErrorCode.INVALID_MULTI_PROVIDER,
+            'Unexpected type of the `ENVIRONMENT_INITIALIZER` token value ' +
+                `(expected an array, but got ${typeof initializers}). ` +
+                'Please check that the `ENVIRONMENT_INITIALIZER` token is configured as a ' +
+                '`multi: true` provider.');
+      }
       for (const initializer of initializers) {
         initializer();
       }

packages/core/src/errors.ts

@@ -32,6 +32,7 @@ export const enum RuntimeErrorCode {
   INJECTOR_ALREADY_DESTROYED = 205,
   PROVIDER_IN_WRONG_CONTEXT = 207,
   MISSING_INJECTION_TOKEN = 208,
+  INVALID_MULTI_PROVIDER = 209,
 
   // Template Errors
   MULTIPLE_COMPONENTS_MATCH = -300,

packages/core/test/acceptance/environment_injector_spec.ts

@@ -96,7 +96,7 @@ describe('environment injector', () => {
        expect(cRef.instance.service).toBeInstanceOf(Service);
      });
 
-  it('should support the ENVIRONMENT_INITIALIZER muli-token', () => {
+  it('should support the ENVIRONMENT_INITIALIZER multi-token', () => {
     let initialized = false;
     const parentEnvInjector = TestBed.inject(EnvironmentInjector);
     createEnvironmentInjector(
@@ -110,6 +110,20 @@ describe('environment injector', () => {
     expect(initialized).toBeTrue();
   });
 
+  it('should throw when the ENVIRONMENT_INITIALIZER is not a multi-token', () => {
+    const parentEnvInjector = TestBed.inject(EnvironmentInjector);
+    const providers = [{
+      provide: ENVIRONMENT_INITIALIZER,
+      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.');
+  });
+
   it('should adopt environment-scoped providers', () => {
     const parentEnvInjector = TestBed.inject(EnvironmentInjector);
     const injector = createEnvironmentInjector([], parentEnvInjector);