backport: fix prerender issue with intercepting routes + generateStaticParams (#75170)

Backports the testcase added in
#75167 in
[9bf61bc](9bf61bc).

Confirmed failure via [this
run](https://github.com/vercel/next.js/actions/runs/12898849331/job/35966678688?pr=75170)

Adds the fix in
[0ab1e32](0ab1e32).
This change is identical to the code used in canary, which was added as
part of the `rootParams` feature via
#73816
([ref](https://github.com/vercel/next.js/blob/d12e2e82b778eef8393f47944a258a55c6c508fe/packages/next/src/build/static-paths/app.ts#L316-L317))

This regression was caused by `segments` containing all possible
segments (including parallel routes), not just the page segment. As a
result, `paramKeys` was incorrectly being calculated. We don't need to
traverse the segments to determine the param keys: we have the route
regex & matcher, it's more reliable to extract it from that.

Author: ztanner

packages/next/src/build/utils.ts

@@ -1289,18 +1289,8 @@ export async function buildAppStaticPaths({
     minimalMode: ciEnvironment.hasNextSupport,
   })
 
-  const paramKeys = new Set<string>()
-
-  const staticParamKeys = new Set<string>()
-  for (const segment of segments) {
-    if (segment.param) {
-      paramKeys.add(segment.param)
-
-      if (segment.config?.dynamicParams === false) {
-        staticParamKeys.add(segment.param)
-      }
-    }
-  }
+  const regex = getRouteRegex(page)
+  const paramKeys = Object.keys(getRouteMatcher(regex)(page) || {})
 
   const afterRunner = new AfterRunner()
 
@@ -1417,7 +1407,7 @@ export async function buildAppStaticPaths({
   // Determine if all the segments have had their parameters provided. If there
   // was no dynamic parameters, then we've collected all the params.
   const hadAllParamsGenerated =
-    paramKeys.size === 0 ||
+    paramKeys.length === 0 ||
     (routeParams.length > 0 &&
       routeParams.every((params) => {
         for (const key of paramKeys) {

test/e2e/app-dir/interception-dynamic-segment/app/@modal/[...catchAll]/page.tsx

@@ -0,0 +1,3 @@
+export default function CatchAll() {
+  return null
+}

test/e2e/app-dir/interception-dynamic-segment/app/@modal/generate-static-params/(.)[slug]/page.tsx

@@ -0,0 +1,3 @@
+export default function Page() {
+  return 'intercepted'
+}

test/e2e/app-dir/interception-dynamic-segment/app/generate-static-params/[slug]/page.tsx

@@ -0,0 +1,19 @@
+type Props = {
+  params: Promise<{ slug: string }>
+}
+
+export default async function Page({ params }: Props) {
+  const { slug } = await params
+  return <div>Hello {slug}</div>
+}
+
+export function generateStaticParams() {
+  return [
+    { slug: 'a' },
+    { slug: 'b' },
+    { slug: 'c' },
+    { slug: 'd' },
+    { slug: 'e' },
+    { slug: 'f' },
+  ]
+}

test/e2e/app-dir/interception-dynamic-segment/interception-dynamic-segment.test.ts

@@ -2,7 +2,7 @@ import { nextTestSetup } from 'e2e-utils'
 import { check } from 'next-test-utils'
 
 describe('interception-dynamic-segment', () => {
-  const { next } = nextTestSetup({
+  const { next, isNextStart } = nextTestSetup({
     files: __dirname,
   })
 
@@ -15,4 +15,13 @@ describe('interception-dynamic-segment', () => {
     await check(() => browser.elementById('modal').text(), '')
     await check(() => browser.elementById('children').text(), /not intercepted/)
   })
+
+  if (isNextStart) {
+    it('should correctly prerender segments with generateStaticParams', async () => {
+      expect(next.cliOutput).toContain('/generate-static-params/a')
+      const res = await next.fetch('/generate-static-params/a')
+      expect(res.status).toBe(200)
+      expect(res.headers.get('x-nextjs-cache')).toBe('HIT')
+    })
+  }
 })