fix(router): attempt to resolve component resources in JIT mode (#63062)

In #62758 we started loading the component resources during bootstrap in JIT mode to ensure that they're in place by the time we create the component. This won't work for lazy-loaded components in the router, because they don't exist at bootstrap time.

These changes add similar logic when the router loads a component.

PR Close #63062

packages/core/test/bundling/router/bundle.golden_symbols.json

@@ -903,6 +903,7 @@
       "matchWithChecks",
       "materializeViewResults",
       "matrixParamsMatch",
+      "maybeResolveResources",
       "maybeReturnReactiveLViewConsumer",
       "maybeSchedule",
       "maybeUnwrapDefaultExport",

packages/router/src/router_config_loader.ts

@@ -16,9 +16,10 @@ import {
   NgModuleFactory,
   runInInjectionContext,
   Type,
+  ɵresolveComponentResources as resolveComponentResources,
 } from '@angular/core';
 import {ConnectableObservable, from, Observable, of, Subject} from 'rxjs';
-import {finalize, map, mergeMap, refCount, tap} from 'rxjs/operators';
+import {finalize, map, mergeMap, refCount, switchMap, tap} from 'rxjs/operators';
 
 import {DefaultExport, LoadedRouterConfig, Route, Routes} from './models';
 import {wrapIntoObservable} from './utils/collection';
@@ -61,6 +62,7 @@ export class RouterConfigLoader {
       runInInjectionContext(injector, () => route.loadComponent!()),
     ).pipe(
       map(maybeUnwrapDefaultExport),
+      switchMap(maybeResolveResources),
       tap((component) => {
         if (this.onLoadEndListener) {
           this.onLoadEndListener(route);
@@ -130,6 +132,7 @@ export function loadChildren(
     runInInjectionContext(parentInjector, () => route.loadChildren!()),
   ).pipe(
     map(maybeUnwrapDefaultExport),
+    switchMap(maybeResolveResources),
     mergeMap((t) => {
       if (t instanceof NgModuleFactory || Array.isArray(t)) {
         return of(t);
@@ -177,3 +180,19 @@ function maybeUnwrapDefaultExport<T>(input: T | DefaultExport<T>): T {
   // subject to property renaming, so we reference it with bracket access.
   return isWrappedDefaultExport(input) ? input['default'] : input;
 }
+
+function maybeResolveResources<T>(value: T): Promise<T> | Observable<T> {
+  // In JIT mode we usually resolve the resources of components on bootstrap, however
+  // that won't have happened for lazy-loaded components. Attempt to load any pending
+  // resources again here.
+  if ((typeof ngJitMode === 'undefined' || ngJitMode) && typeof fetch === 'function') {
+    return resolveComponentResources(fetch)
+      .catch((error) => {
+        console.error(error);
+        return Promise.resolve();
+      })
+      .then(() => value);
+  }
+
+  return of(value);
+}