[next] Ensure all static routes have static streaming lambda path (#11259)

When there's a match for a prerender, the dynamic query parameters will
not be provided via the `x-now-route-matches`. This ensures that when
generating any static route that the static streaming lambda path is
used if it's provided, ensuring that when a page is generated via
`generateStaticParams`:

```tsx
// app/blog/[slug]/page.tsx

type Props = {
  params: {
    slug: string
  }
}

export function generateStaticParams() {
  return [{ slug: "one" }, { slug: "two" }, { slug: "three" }]
}

export default function BlogPage({ slug }: Props) {
  // ...
}
```

That we use the specific routes (`/blog/one`, `/blog/two`, and
`/blog/three`) for the partial prerendering streaming path instead of
the paramatarized pathname (`/blog/[slug]`) as the rewrites won't be
matched once a match for a prerender has been found.

This additionally updates the tests to ensure that the correct pathname
is observed (this was previously silently failing).

packages/next/src/utils.ts

@@ -1938,7 +1938,6 @@ type OnPrerenderRouteArgs = {
   routesManifest?: RoutesManifest;
   isCorrectNotFoundRoutes?: boolean;
   isEmptyAllowQueryForPrendered?: boolean;
-  omittedPrerenderRoutes: ReadonlySet<string>;
 };
 let prerenderGroup = 1;
 
@@ -1975,7 +1974,6 @@ export const onPrerenderRoute =
       routesManifest,
       isCorrectNotFoundRoutes,
       isEmptyAllowQueryForPrendered,
-      omittedPrerenderRoutes,
     } = prerenderRouteArgs;
 
     if (isBlocking && isFallback) {
@@ -2211,12 +2209,19 @@ export const onPrerenderRoute =
       initialStatus = 404;
     }
 
+    /**
+     * If the route key had an `/index` suffix added, we need to note it so we
+     * can remove it from the output path later accurately.
+     */
+    let addedIndexSuffix = false;
+
     if (isAppPathRoute) {
       // for literal index routes we need to append an additional /index
       // due to the proxy's normalizing for /index routes
       if (routeKey !== '/index' && routeKey.endsWith('/index')) {
         routeKey = `${routeKey}/index`;
         routeFileNoExt = routeKey;
+        addedIndexSuffix = true;
       }
     }
 
@@ -2225,6 +2230,7 @@ export const onPrerenderRoute =
     if (!isAppPathRoute) {
       outputPathPage = normalizeIndexOutput(outputPathPage, isServerMode);
     }
+
     const outputPathPageOrig = path.posix.join(
       entryDirectory,
       origRouteFileNoExt
@@ -2408,20 +2414,25 @@ export const onPrerenderRoute =
           );
         }
 
-        // If a source route exists, and it's not listed as an omitted route,
-        // then use the src route as the basis for the experimental streaming
-        // lambda path. If the route doesn't have a source route or it's not
-        // omitted, then use the more specific `routeKey` as the basis.
-        if (srcRoute && !omittedPrerenderRoutes.has(srcRoute)) {
+        // Try to get the experimental streaming lambda path for the specific
+        // static route first, then try the srcRoute if it doesn't exist. If we
+        // can't find it at all, this constitutes an error.
+        experimentalStreamingLambdaPath = experimentalStreamingLambdaPaths.get(
+          pathnameToOutputName(entryDirectory, routeKey, addedIndexSuffix)
+        );
+        if (!experimentalStreamingLambdaPath && srcRoute) {
           experimentalStreamingLambdaPath =
             experimentalStreamingLambdaPaths.get(
               pathnameToOutputName(entryDirectory, srcRoute)
             );
-        } else {
-          experimentalStreamingLambdaPath =
-            experimentalStreamingLambdaPaths.get(
-              pathnameToOutputName(entryDirectory, routeKey)
-            );
+        }
+
+        if (!experimentalStreamingLambdaPath) {
+          throw new Error(
+            `Invariant: experimentalStreamingLambdaPath is undefined for routeKey=${routeKey} and srcRoute=${
+              srcRoute ?? 'null'
+            }`
+          );
         }
       }
 
@@ -2651,8 +2662,20 @@ export function getNextServerPath(nextVersion: string) {
     : 'next/dist/next-server/server';
 }
 
-export function pathnameToOutputName(entryDirectory: string, pathname: string) {
-  if (pathname === '/') pathname = '/index';
+function pathnameToOutputName(
+  entryDirectory: string,
+  pathname: string,
+  addedIndexSuffix = false
+) {
+  if (pathname === '/') {
+    pathname = '/index';
+  }
+  // If the `/index` was added for a route that ended in `/index` we need to
+  // strip the second one off before joining it with the entryDirectory.
+  else if (addedIndexSuffix) {
+    pathname = pathname.replace(/\/index$/, '');
+  }
+
   return path.posix.join(entryDirectory, pathname);
 }