feat(core): add mergeApplicationConfig method (#49253)

This commits add a utility method to merge multiple `ApplicationConfiguration` into one from left to right.  This is useful for server rendering were an application might have several configurations.

Usage Example:
```ts
const config = mergeApplicationConfig(appConfig, appServerConfig);
```

PR Close #49253

Author: alan-agius4

goldens/public-api/core/index.md

@@ -912,6 +912,9 @@ export const LOCALE_ID: InjectionToken<string>;
 // @public
 export function makeEnvironmentProviders(providers: (Provider | EnvironmentProviders)[]): EnvironmentProviders;
 
+// @public
+export function mergeApplicationConfig(...configs: ApplicationConfig[]): ApplicationConfig;
+
 // @public
 export enum MissingTranslationStrategy {
     // (undocumented)

packages/core/src/application_config.ts

@@ -20,3 +20,17 @@ export interface ApplicationConfig {
    */
   providers: Array<Provider|EnvironmentProviders>;
 }
+
+/**
+ * Merge multiple application configurations from left to right.
+ *
+ * @param configs Two or more configurations to be merged.
+ * @returns A merged [ApplicationConfig](api/core/ApplicationConfig).
+ *
+ * @publicApi
+ */
+export function mergeApplicationConfig(...configs: ApplicationConfig[]): ApplicationConfig {
+  return configs.reduce((prev, curr) => {
+    return Object.assign(prev, curr, {providers: [...prev.providers, ...curr.providers]});
+  }, {providers: []});
+}

packages/core/src/core.ts

@@ -40,7 +40,7 @@ export {Sanitizer} from './sanitization/sanitizer';
 export {createNgModule, createNgModuleRef, createEnvironmentInjector} from './render3/ng_module_ref';
 export {createComponent, reflectComponentType, ComponentMirror} from './render3/component';
 export {isStandalone} from './render3/definition';
-export {ApplicationConfig} from './application_config';
+export {ApplicationConfig, mergeApplicationConfig} from './application_config';
 
 import {global} from './util/global';
 if (typeof ngDevMode !== 'undefined' && ngDevMode) {

packages/core/test/application_config_spec.ts

@@ -0,0 +1,56 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+import {ApplicationConfig, InjectionToken, mergeApplicationConfig} from '@angular/core';
+
+describe('ApplicationConfig', () => {
+  describe('mergeApplicationConfig', () => {
+    const FOO_TOKEN = new InjectionToken('foo');
+    const BAR_TOKEN = new InjectionToken('bar');
+    const BUZ_TOKEN = new InjectionToken('buz');
+
+    const BASE_CONFIG: ApplicationConfig = {
+      providers: [{provide: FOO_TOKEN, useValue: 'foo'}],
+    };
+
+    const APP_CONFIG_EXPECT: ApplicationConfig = {
+      providers: [
+        {provide: FOO_TOKEN, useValue: 'foo'},
+        {provide: BAR_TOKEN, useValue: 'bar'},
+        {provide: BUZ_TOKEN, useValue: 'buz'},
+      ]
+    };
+
+    it('should merge 2 configs from left to right', () => {
+      const extraConfig: ApplicationConfig = {
+        providers: [
+          {provide: BAR_TOKEN, useValue: 'bar'},
+          {provide: BUZ_TOKEN, useValue: 'buz'},
+        ],
+      };
+
+      const config = mergeApplicationConfig(BASE_CONFIG, extraConfig);
+      expect(config).toEqual(APP_CONFIG_EXPECT);
+    });
+
+    it('should merge more than 2 configs from left to right', () => {
+      const extraConfigOne: ApplicationConfig = {
+        providers: [
+          {provide: BAR_TOKEN, useValue: 'bar'},
+        ],
+      };
+      const extraConfigTwo: ApplicationConfig = {
+        providers: [
+          {provide: BUZ_TOKEN, useValue: 'buz'},
+        ],
+      };
+
+      const config = mergeApplicationConfig(BASE_CONFIG, extraConfigOne, extraConfigTwo);
+      expect(config).toEqual(APP_CONFIG_EXPECT);
+    });
+  });
+});