fix dynamic param extraction for interception routes (#67400)

### What
When using `generateStaticParams` with interception routes, the
interception would never occur, and instead an MPA navigation would take
place to the targeted link.

### Why
For interception rewrites, we use a `__NEXT_EMPTY_PARAM__` marker (in
place of the actual param slot, eg `:locale`) for any params that are
discovered prior to the interception marker. This is because during
route resolution, the `params` for the interception route might not
contain the same `params` for the page that triggered the interception.
The dynamic params are then extracted from `FlightRouterState` at render
time. However, when `generateStaticParams` is present, the
`FlightRouterState` header is stripped from the request, so it isn't
able to extract the dynamic params and so the router thinks the new tree
is a new root layout, hence the MPA navigation.

### How
This removes the `__NEXT_EMPTY_PARAM__` hack and several spots where we
were forcing interception routes to be dynamic as a workaround to the
above bug. Now when resolving the route, if the request was to an
interception route, we extract the dynamic params from the request
before constructing the final rewritten URL. This will ensure that the
params from the "current" route are available in addition to the params
from the interception route without needing to defer until render.

Fixes #65192
Fixes #52880

packages/next/src/build/index.ts

@@ -166,7 +166,6 @@ import {
 import { getStartServerInfo, logStartInfo } from '../server/lib/app-info-log'
 import type { NextEnabledDirectories } from '../server/base-server'
 import { hasCustomExportOutput } from '../export/utils'
-import { isInterceptionRouteAppPath } from '../server/lib/interception-routes'
 import {
   getTurbopackJsConfig,
   handleEntrypoints,
@@ -2106,8 +2105,6 @@ export default async function build(
                           }
 
                           const appConfig = workerResult.appConfig || {}
-                          const isInterceptionRoute =
-                            isInterceptionRouteAppPath(page)
                           if (appConfig.revalidate !== 0) {
                             const isDynamic = isDynamicRoute(page)
                             const hasGenerateStaticParams =
@@ -2124,27 +2121,22 @@ export default async function build(
                             }
 
                             // Mark the app as static if:
-                            // - It's not an interception route (these currently depend on request headers and cannot be computed at build)
                             // - It has no dynamic param
                             // - It doesn't have generateStaticParams but `dynamic` is set to
                             //   `error` or `force-static`
-                            if (!isInterceptionRoute) {
-                              if (!isDynamic) {
-                                appStaticPaths.set(originalAppPath, [page])
-                                appStaticPathsEncoded.set(originalAppPath, [
-                                  page,
-                                ])
-                                isStatic = true
-                              } else if (
-                                !hasGenerateStaticParams &&
-                                (appConfig.dynamic === 'error' ||
-                                  appConfig.dynamic === 'force-static')
-                              ) {
-                                appStaticPaths.set(originalAppPath, [])
-                                appStaticPathsEncoded.set(originalAppPath, [])
-                                isStatic = true
-                                isRoutePPREnabled = false
-                              }
+                            if (!isDynamic) {
+                              appStaticPaths.set(originalAppPath, [page])
+                              appStaticPathsEncoded.set(originalAppPath, [page])
+                              isStatic = true
+                            } else if (
+                              !hasGenerateStaticParams &&
+                              (appConfig.dynamic === 'error' ||
+                                appConfig.dynamic === 'force-static')
+                            ) {
+                              appStaticPaths.set(originalAppPath, [])
+                              appStaticPathsEncoded.set(originalAppPath, [])
+                              isStatic = true
+                              isRoutePPREnabled = false
                             }
                           }
 

packages/next/src/client/components/app-router.tsx

@@ -61,8 +61,7 @@ import { unresolvedThenable } from './unresolved-thenable'
 import { NEXT_RSC_UNION_QUERY } from './app-router-headers'
 import { removeBasePath } from '../remove-base-path'
 import { hasBasePath } from '../has-base-path'
-import { PAGE_SEGMENT_KEY } from '../../shared/lib/segment'
-import type { Params } from '../../shared/lib/router/utils/route-matcher'
+import { getSelectedParams } from './router-reducer/compute-changed-path'
 import type { FlightRouterState } from '../../server/app-render/types'
 const isServer = typeof window === 'undefined'
 
@@ -98,36 +97,6 @@ export function urlToUrlWithoutFlightMarker(url: string): URL {
   return urlWithoutFlightParameters
 }
 
-// this function performs a depth-first search of the tree to find the selected
-// params
-function getSelectedParams(
-  currentTree: FlightRouterState,
-  params: Params = {}
-): Params {
-  const parallelRoutes = currentTree[1]
-
-  for (const parallelRoute of Object.values(parallelRoutes)) {
-    const segment = parallelRoute[0]
-    const isDynamicParameter = Array.isArray(segment)
-    const segmentValue = isDynamicParameter ? segment[1] : segment
-    if (!segmentValue || segmentValue.startsWith(PAGE_SEGMENT_KEY)) continue
-
-    // Ensure catchAll and optional catchall are turned into an array
-    const isCatchAll =
-      isDynamicParameter && (segment[2] === 'c' || segment[2] === 'oc')
-
-    if (isCatchAll) {
-      params[segment[0]] = segment[1].split('/')
-    } else if (isDynamicParameter) {
-      params[segment[0]] = segment[1]
-    }
-
-    params = getSelectedParams(parallelRoute, params)
-  }
-
-  return params
-}
-
 type AppRouterProps = Omit<
   Omit<InitialRouterStateParameters, 'isServer' | 'location'>,
   'initialParallelRoutes'

packages/next/src/client/components/router-reducer/compute-changed-path.ts

@@ -3,6 +3,7 @@ import type {
   Segment,
 } from '../../../server/app-render/types'
 import { INTERCEPTION_ROUTE_MARKERS } from '../../../server/lib/interception-routes'
+import type { Params } from '../../../shared/lib/router/utils/route-matcher'
 import {
   isGroupSegment,
   DEFAULT_SEGMENT_KEY,
@@ -130,3 +131,34 @@ export function computeChangedPath(
   // lightweight normalization to remove route groups
   return normalizeSegments(changedPath.split('/'))
 }
+
+/**
+ * Recursively extracts dynamic parameters from FlightRouterState.
+ */
+export function getSelectedParams(
+  currentTree: FlightRouterState,
+  params: Params = {}
+): Params {
+  const parallelRoutes = currentTree[1]
+
+  for (const parallelRoute of Object.values(parallelRoutes)) {
+    const segment = parallelRoute[0]
+    const isDynamicParameter = Array.isArray(segment)
+    const segmentValue = isDynamicParameter ? segment[1] : segment
+    if (!segmentValue || segmentValue.startsWith(PAGE_SEGMENT_KEY)) continue
+
+    // Ensure catchAll and optional catchall are turned into an array
+    const isCatchAll =
+      isDynamicParameter && (segment[2] === 'c' || segment[2] === 'oc')
+
+    if (isCatchAll) {
+      params[segment[0]] = segment[1].split('/')
+    } else if (isDynamicParameter) {
+      params[segment[0]] = segment[1]
+    }
+
+    params = getSelectedParams(parallelRoute, params)
+  }
+
+  return params
+}

packages/next/src/lib/generate-interception-routes-rewrites.ts

@@ -1,7 +1,6 @@
 import { pathToRegexp } from 'next/dist/compiled/path-to-regexp'
 import { NEXT_URL } from '../client/components/app-router-headers'
 import {
-  INTERCEPTION_ROUTE_MARKERS,
   extractInterceptionRouteInformation,
   isInterceptionRouteAppPath,
 } from '../server/lib/interception-routes'
@@ -21,31 +20,6 @@ function toPathToRegexpPath(path: string): string {
   })
 }
 
-// for interception routes we don't have access to the dynamic segments from the
-// referrer route so we mark them as noop for the app renderer so that it
-// can retrieve them from the router state later on. This also allows us to
-// compile the route properly with path-to-regexp, otherwise it will throw
-function voidParamsBeforeInterceptionMarker(path: string): string {
-  let newPath = []
-
-  let foundInterceptionMarker = false
-  for (const segment of path.split('/')) {
-    if (
-      INTERCEPTION_ROUTE_MARKERS.find((marker) => segment.startsWith(marker))
-    ) {
-      foundInterceptionMarker = true
-    }
-
-    if (segment.startsWith(':') && !foundInterceptionMarker) {
-      newPath.push('__NEXT_EMPTY_PARAM__')
-    } else {
-      newPath.push(segment)
-    }
-  }
-
-  return newPath.join('/')
-}
-
 export function generateInterceptionRoutesRewrites(
   appPaths: string[],
   basePath = ''
@@ -62,9 +36,7 @@ export function generateInterceptionRoutesRewrites(
       }/(.*)?`
 
       const normalizedInterceptedRoute = toPathToRegexpPath(interceptedRoute)
-      const normalizedAppPath = voidParamsBeforeInterceptionMarker(
-        toPathToRegexpPath(appPath)
-      )
+      const normalizedAppPath = toPathToRegexpPath(appPath)
 
       // pathToRegexp returns a regex that matches the path, but we need to
       // convert it to a string that can be used in a header value

packages/next/src/server/app-render/app-render.tsx

@@ -34,7 +34,6 @@ import {
   continueDynamicHTMLResume,
   continueDynamicDataResume,
 } from '../stream-utils/node-web-streams-helper'
-import { canSegmentBeOverridden } from '../../client/components/match-segments'
 import { stripInternalQueries } from '../internal-utils'
 import {
   NEXT_ROUTER_PREFETCH_HEADER,
@@ -103,7 +102,6 @@ import {
   StaticGenBailoutError,
   isStaticGenBailoutError,
 } from '../../client/components/static-generation-bailout'
-import { isInterceptionRouteAppPath } from '../lib/interception-routes'
 import { getStackWithoutErrorMessage } from '../../lib/format-server-error'
 import {
   usedDynamicAPIs,
@@ -162,63 +160,14 @@ function createNotFoundLoaderTree(loaderTree: LoaderTree): LoaderTree {
   return ['', {}, loaderTree[2]]
 }
 
-/* This method is important for intercepted routes to function:
- * when a route is intercepted, e.g. /blog/[slug], it will be rendered
- * with the layout of the previous page, e.g. /profile/[id]. The problem is
- * that the loader tree needs to know the dynamic param in order to render (id and slug in the example).
- * Normally they are read from the path but since we are intercepting the route, the path would not contain id,
- * so we need to read it from the router state.
- */
-function findDynamicParamFromRouterState(
-  flightRouterState: FlightRouterState | undefined,
-  segment: string
-): {
-  param: string
-  value: string | string[] | null
-  treeSegment: Segment
-  type: DynamicParamTypesShort
-} | null {
-  if (!flightRouterState) {
-    return null
-  }
-
-  const treeSegment = flightRouterState[0]
-
-  if (canSegmentBeOverridden(segment, treeSegment)) {
-    if (!Array.isArray(treeSegment) || Array.isArray(segment)) {
-      return null
-    }
-
-    return {
-      param: treeSegment[0],
-      value: treeSegment[1],
-      treeSegment: treeSegment,
-      type: treeSegment[2],
-    }
-  }
-
-  for (const parallelRouterState of Object.values(flightRouterState[1])) {
-    const maybeDynamicParam = findDynamicParamFromRouterState(
-      parallelRouterState,
-      segment
-    )
-    if (maybeDynamicParam) {
-      return maybeDynamicParam
-    }
-  }
-
-  return null
-}
-
 export type CreateSegmentPath = (child: FlightSegmentPath) => FlightSegmentPath
 
 /**
  * Returns a function that parses the dynamic segment and return the associated value.
  */
 function makeGetDynamicParamFromSegment(
   params: { [key: string]: any },
-  pagePath: string,
-  flightRouterState: FlightRouterState | undefined
+  pagePath: string
 ): GetDynamicParamFromSegment {
   return function getDynamicParamFromSegment(
     // [slug] / [[slug]] / [...slug]
@@ -233,11 +182,6 @@ function makeGetDynamicParamFromSegment(
 
     let value = params[key]
 
-    // this is a special marker that will be present for interception routes
-    if (value === '__NEXT_EMPTY_PARAM__') {
-      value = undefined
-    }
-
     if (Array.isArray(value)) {
       value = value.map((i) => encodeURIComponent(i))
     } else if (typeof value === 'string') {
@@ -283,8 +227,6 @@ function makeGetDynamicParamFromSegment(
           treeSegment: [key, value.join('/'), dynamicParamType],
         }
       }
-
-      return findDynamicParamFromRouterState(flightRouterState, segment)
     }
 
     const type = getShortDynamicParamType(segmentParam.type)
@@ -820,16 +762,10 @@ async function renderToHTMLOrFlightImpl(
    * Router state provided from the client-side router. Used to handle rendering
    * from the common layout down. This value will be undefined if the request
    * is not a client-side navigation request or if the request is a prefetch
-   * request (except when it's a prefetch request for an interception route
-   * which is always dynamic).
+   * request.
    */
   const shouldProvideFlightRouterState =
-    isRSCRequest &&
-    (!isPrefetchRSCRequest ||
-      !isRoutePPREnabled ||
-      // Interception routes currently depend on the flight router state to
-      // extract dynamic params.
-      isInterceptionRouteAppPath(pagePath))
+    isRSCRequest && (!isPrefetchRSCRequest || !isRoutePPREnabled)
 
   const parsedFlightRouterState = parseAndValidateFlightRouterState(
     req.headers[NEXT_ROUTER_STATE_TREE.toLowerCase()]
@@ -854,10 +790,7 @@ async function renderToHTMLOrFlightImpl(
 
   const getDynamicParamFromSegment = makeGetDynamicParamFromSegment(
     params,
-    pagePath,
-    // `FlightRouterState` is unconditionally provided here because this method uses it
-    // to extract dynamic params as a fallback if they're not present in the path.
-    parsedFlightRouterState
+    pagePath
   )
 
   // Get the nonce from the incoming request if it has one.

packages/next/src/server/app-render/parse-and-validate-flight-router-state.tsx

@@ -2,6 +2,15 @@ import type { FlightRouterState } from './types'
 import { flightRouterStateSchema } from './types'
 import { assert } from 'next/dist/compiled/superstruct'
 
+export function parseAndValidateFlightRouterState(
+  stateHeader: string | string[]
+): FlightRouterState
+export function parseAndValidateFlightRouterState(
+  stateHeader: undefined
+): undefined
+export function parseAndValidateFlightRouterState(
+  stateHeader: string | string[] | undefined
+): FlightRouterState | undefined
 export function parseAndValidateFlightRouterState(
   stateHeader: string | string[] | undefined
 ): FlightRouterState | undefined {