Fix(typedRoutes): respect trailingSlash config in generated routes

[prave01]

Fix(typedRoutes): respect trailingSlash config in generated routes - Issue #83185

Mandatory checks :

✅ Tests added and verified (/test/e2e/typed-routes-trailing-slash/typed-routes-trailing-slash.test.ts)
✅ Checked with locally build and exported Tarball version
✅ Works for both app and pages router

About the issue

• The issue is, after enabling trailingSlash=true and typedRoutes=true in nextjs.config, he could't able to find the snippets for generated routes types with trailing slash behind.

How i solved it

• Originally, generateLinkTypesFile only received the routesManifest, so it always wrote routes without considering trailingSlash.
• I updated the function signature to also accept the full NextConfigComplete object.

Changes made

• Passed config into generateLinkTypesFile:

/packages/next/src/server/lib/router-utils/route-types-utils.ts

await fs.promises.writeFile(
  linkTypesPath,
  generateLinkTypesFile(manifest, config)
)

• Updated function signature:

/packages/next/src/server/lib/router-utils/typegen.ts

export function generateLinkTypesFile(
  routesManifest: RouteTypesManifest,
  config: NextConfigComplete
): string

• Modified route serialization logic to respect trailingSlash:

/packages/next/src/server/lib/router-utils/typegen.ts

staticRouteTypes.push(
  config.trailingSlash && route !== '/' ? `${routeType}/` : routeType
)

---

About Test

• ✅ Sets up a headless Next.js app with trailingSlash: true and typedRoutes: true.
• ✅ Checks the generated link.d.ts file includes / and /dashboard/ as static routes.
• ✅ Confirms that no dynamic routes are generated (DynamicRoutes = never).
• ✅ Launches in headless and navigates to /dashboard/ via a typed <Link>.
• ✅ Verifies the URL has the trailing slash (/dashboard/).
• ✅ Asserts that the page renders correctly with <h1>Dashboard</h1>.

Why this test matters

• Prevents regressions: ensures trailingSlash + typedRoutes always behave consistently.
• Covers both build-time types and runtime navigation.

---

Reference - #23988

Closes NEXT-
Fixes #83185