@angular/ssr: page under nested empty-path routes is prerendered without the modulepreload hints of its lazy chunks (regression since 19.1.6) #34320

Command

build

Is this a regression?

Yes, the previous version in which this bug was not present was: 19.1.5

Description

A prerendered page reached through an empty-path route nested under another empty-path route (a componentless '' route whose '' child is a loadChildren, whose own '' route is a loadComponent) is emitted without any <link rel="modulepreload"> hint for its own lazy chunks. A sibling page reached through a non-empty path with exactly the same lazy depth ('pricing' → loadChildren → '' loadComponent) gets both of its hints. The page itself renders correctly; only the hints are missing.

Measured with 22.2.2, outputMode: "static" (index.csr.html has 0 hints):

Same nested routes on 19.1.5 vs 19.1.6 (both builds share 2 initial chunks, which index.csr.html also has):

The chunk hashes are identical across these builds; only @angular/ssr makes the difference.

Likely cause (packages/angular/ssr/src/routes/ng-routes.ts): traverseRoutesConfig keys an empty-path route as addTrailingSlash(currentRoutePath). Under a non-empty parent the parent and its '' child get different keys (/pricing and /pricing/), which RouteTree.insert later merges with the last entry winning, the leaf that carries the accumulated preload. Under an empty-path parent both get the same key (/, or /es/ for es → '' → ''), and getRoutesFromAngularRouterConfig keeps only the first result per key (seenRoutes, added in 5bf5e5f "fix(@angular/ssr): prioritize the first matching route over subsequent ones", #29539). The first result is the outer route, yielded before handleRoute appends its loadChildren preloads and before any descendant's loadComponent preloads, so the leaf's metadata with the preloads is dropped. That dedupe is right for competing sibling routes with the same path; here the later entry is a descendant in the same match chain, the route the router actually activates.

Expected: the prerendered page carries the hints of the route chain that renders it, as on 19.1.5 (for example, let a later result replace the kept one, or merge its preload, when it is a descendant of it rather than a sibling).

Real-world impact: our home page had 3 modulepreload hints against 12 on /pricing; flattening the home route to a top-level loadComponent gave 9.

Minimal Reproduction

npx -p @angular/cli@22.2.2 ng new repro --ssr --routing --style=css --skip-git --skip-tests --defaults --ai-config=none --package-manager=npm
cd repro
# angular.json: set "outputMode": "static"
# src/app/app.html: replace its content with <router-outlet />  (optional, only trims the placeholder)
# app.routes.server.ts stays as generated: [{ path: '**', renderMode: RenderMode.Prerender }]

src/app/app.routes.ts

import { Routes } from '@angular/router';

export const routes: Routes = [
  {
    path: '',
    children: [
      { path: '', pathMatch: 'full', loadChildren: () => import('./home/home.routes') },
      { path: 'pricing', loadChildren: () => import('./pricing/pricing.routes') },
    ],
  },
];

src/app/home/home.routes.ts (and src/app/pricing/pricing.routes.ts, the same with ./pricing-page)

import { Routes } from '@angular/router';

export default [{ path: '', loadComponent: () => import('./home-page') }] satisfies Routes;

src/app/home/home-page.ts (and src/app/pricing/pricing-page.ts, the same with PricingPage)

import { Component } from '@angular/core';

@Component({ template: '<h1>Home page</h1>' })
export default class HomePage {}

npx ng build
grep -o '<link rel="modulepreload"[^>]*>' dist/repro/browser/index.html          # nothing
grep -o '<link rel="modulepreload"[^>]*>' dist/repro/browser/pricing/index.html  # 2 links

Workaround that brings / back to its hint, the page as a top-level route:

export const routes: Routes = [
  { path: '', pathMatch: 'full', loadComponent: () => import('./home/home-page') },
  { path: 'pricing', loadChildren: () => import('./pricing/pricing.routes') },
];

Exception or Error

None. The build succeeds ("Prerendered 2 static routes.") and both pages render their content; only the modulepreload hints of `/` are missing.

Your Environment

Angular CLI       : 22.2.2
Angular           : 22.2.2
Node.js           : 24.21.0
Package Manager   : npm 11.19.0
Operating System  : darwin arm64

@angular/build            22.2.2
@angular/cli              22.2.2
@angular/common           22.2.2
@angular/compiler         22.2.2
@angular/compiler-cli     22.2.2
@angular/core             22.2.2
@angular/forms            22.2.2
@angular/platform-browser 22.2.2
@angular/platform-server  22.2.2
@angular/router           22.2.2
@angular/ssr              22.2.2
rxjs                      7.8.2
typescript                6.0.3

Anything else relevant?

• At the root, one empty-path level under another is enough: a top-level { path: '', pathMatch: 'full', loadChildren: () => import('./home/home.routes') } with no componentless wrapper also gives / 0 hints. So removing only the wrapper is not a workaround; the page itself must be the top-level '' route.
• Not specific to the root: { path: 'es', children: [{ path: '', pathMatch: 'full', loadChildren: ... }, { path: 'pricing', loadChildren: ... }] } gives /es 0 hints and /es/pricing 2.
• The per-route preload feature itself worked in 19.1.0–19.1.5; the seenRoutes dedupe appears in 19.1.6 and is still there in 22.2.2.