fix(core): mark NgModule as not the root if APP_ROOT is set to false (#24814)

Tree shakable providers use the APP_ROOT token to determine where to attach themselves. APP_ROOT gets set on NgModule with BrowserModule irrespective of whether it is actually the root(Ex. in case of SSR app where the shell app is first bootstrapped without BrowserModule being the root module).

This change allows a NgModule with BrowserModule to explicitly mark itself as not the root by setting APP_ROOT token to false. This allows tree shakable providers to be attached to the right rott module.

PR Close #24814

packages/core/src/view/ng_module.ts

@@ -43,7 +43,7 @@ export function moduleDef(providers: NgModuleProviderDef[]): NgModuleDefinition
   let isRoot: boolean = false;
   for (let i = 0; i < providers.length; i++) {
     const provider = providers[i];
-    if (provider.token === APP_ROOT) {
+    if (provider.token === APP_ROOT && provider.value === true) {
       isRoot = true;
     }
     if (provider.flags & NodeFlags.TypeNgModule) {

packages/core/test/view/ng_module_spec.ts

@@ -14,6 +14,7 @@ import {NgModuleDefinition, NgModuleProviderDef, NodeFlags} from '@angular/core/
 import {moduleDef, moduleProvideDef, resolveNgModuleDep} from '@angular/core/src/view/ng_module';
 import {createNgModuleRef} from '@angular/core/src/view/refs';
 import {tokenKey} from '@angular/core/src/view/util';
+import {APP_ROOT} from '../../src/di/scope';
 
 class Foo {}
 
@@ -229,4 +230,29 @@ describe('NgModuleRef_ injector', () => {
     ref.destroy();
     expect(Service.destroyed).toBe(1);
   });
+
+  describe('moduleDef', () => {
+    function createProvider(token: any, value: any) {
+      return {
+        index: 0,
+        flags: NodeFlags.TypeValueProvider | NodeFlags.LazyProvider,
+        deps: [], token, value
+      };
+    }
+
+    it('sets isRoot to `true` when APP_ROOT is `true`', () => {
+      const def = moduleDef([createProvider(APP_ROOT, true)]);
+      expect(def.isRoot).toBe(true);
+    });
+
+    it('sets isRoot to `false` when APP_ROOT is absent', () => {
+      const def = moduleDef([]);
+      expect(def.isRoot).toBe(false);
+    });
+
+    it('sets isRoot to `false` when APP_ROOT is `false`', () => {
+      const def = moduleDef([createProvider(APP_ROOT, false)]);
+      expect(def.isRoot).toBe(false);
+    });
+  });
 });