Support the typedRoutes config option (statically typed links) #3075

Summary

Support the stable typedRoutes config option (statically typed links). vinext's typegen already generates .next/types/routes.d.ts with route unions and a ParamMap, which is most of the machinery — what's missing is the typed-links file Next.js emits when typedRoutes: true is set, plus wiring for the config flag. vinext check currently reports experimental.typedRoutes as unsupported, and the stable top-level typedRoutes key isn't in the config support map at all.

Motivation / problem

Apps that enable typedRoutes rely on import type { Route } from 'next' and compile-time validation of href values (e.g. lint/CI guards that keep internal links pointing at real routes). Migrating such an app to vinext silently loses the feature: the vendored Route<T> type stays the string & {} fallback stub, so everything type-checks whether or not the route exists. For codebases that use typed routes as a correctness gate rather than a convenience, this is a migration blocker.

Expected behaviour

With typedRoutes: true in next.config.*:

• Dev, build, and vinext typegen additionally emit the typed-links declaration file (Next 16 writes .next/types/link.d.ts): the __next_route_internal_types__ namespace with StaticRoutes / DynamicRoutes / RouteImpl<T>, plus declare module augmentations for next (real Route<T>), next/link (typed href), next/navigation (typed useRouter, redirect, permanentRedirect), and next/form.
• The generated next-env.d.ts references the new file alongside routes.d.ts.
• vinext check reports typedRoutes as supported, with experimental.typedRoutes treated as a deprecated alias (matching Next, which stabilised the option).

Actual behaviour

• The typedRoutes flag is not read anywhere; only routes.d.ts is generated.
• Route<T> resolves to the vendored stub string & {}, so no href validation occurs.
• check.ts lists experimental.typedRoutes as unsupported — typed routes not implemented; the stable key is absent from CONFIG_SUPPORT.

Reproduction context

Any Next.js 16 App Router project with typedRoutes: true in next.config.ts. Run vinext typegen (or dev/build) and observe that no typed-links declarations are generated and invalid <Link href="/does-not-exist"> values type-check. Observed against vinext main as of 2026-08-25 while scanning a six-app Next 16 monorepo for migration feasibility.

Additional context

Implementation sketch, from reading both codebases:

• Next 16's reference implementation is compact: route-types-utils.js writes link.d.ts from generateLinkTypesFile(manifest) when config.typedRoutes === true. The template ports nearly verbatim, and typegen.ts's existing route model (patternToNextFormat) already produces Next-format patterns for the StaticRoutes / DynamicRoutes unions.
• The vendored type tree (packages/types/next/upstream/dist/) already contains the modules the generated augmentations import from (dist/client/link.d.ts, dist/client/components/redirect-error.d.ts), so the emitted file should type-check without adapting the template's import paths.
• Config plumbing: pass nextConfig.typedRoutes through the writeRouteTypes() call sites in index.ts and the typegen CLI path; warnDeprecatedConfigOptions is the existing hook for the experimental.typedRoutes alias.
• Suggested scope for a first pass: App Router routes only (vinext's typegen currently models only the app dir). Next also folds Pages Router routes and redirect/rewrite sources into the generated unions — those, plus experimental.strictRouteTypes, could be deferred to follow-ups if that helps keep the first PR reviewable.
• Tests would extend tests/typegen.test.ts's existing temp-project harness: static / dynamic / catch-all / route-group cases with the flag on, and a flag-off case asserting no typed-links file is emitted.