next.js

e59eb73b - Compute dev fallback params from the most-specific prerendered route (#95066)

Compute dev fallback params from the most-specific prerendered route (#95066) When Cache Components is enabled, the development server threads a `fallbackParams` request meta for dynamic app routes so the staged render knows which params are not statically known and must be deferred to a later stage. The previous computation walked the prerendered routes from `getStaticPaths` and kept the one with the fewest fallback params, without checking that the route actually matched the requested URL. Consider `/mixed/[lang]/[id]` where `generateStaticParams` covers `lang: 'en'` but not `id`: the prerendered routes are the base `/mixed/[lang]/[id]`, which defers `[lang, id]`, and the covered `/mixed/en/[id]`, which defers only `[id]`. For the request `/mixed/fr/123` the fewest-fallback route is `/mixed/en/[id]`, but `en` does not match `fr`, so applying its `[id]` set left `lang` out of the fallback set and `fr` was treated as a statically known value. Because this meta decides which stage each param resolves in, and the stage decides the environment a replayed `console.log` is attributed to, treating `fr` as static resolved it in the prerender stage instead of deferring it to the runtime stage. The computation now matches the requested URL against each prerendered route with the canonical `getRouteRegex` and, among the routes that match, picks the most-specific one, the one with the fewest fallback params. For `/mixed/fr/123` only the base route matches, so its `[lang, id]` set is used and both params defer, while for `/mixed/en/123` the covered `/mixed/en/[id]` still matches and wins, so `lang` resolves statically and only `id` defers. This mirrors what a production build writes to the prerender manifest, where the server matches the URL to the most-specific prerendered route at request time. The change is development-only, gated on the route module being in dev mode, and production continues to read the manifest. A later change in this stack reads the same `fallbackParams` meta for the Instant Navigation testing API's on-demand shell render, so that path defers the identical per-URL set a production prefetch would.