Remove default fallback behavior when route group is missing a default (

#62370)

This test case was added in #59752, but this doesn't seem like the
correct behavior.

The original PR was intended to be smart about resolving `/default.tsx`
to a route group default (e.g. `/(foo)/default.tsx`) when one wasn't
specified. But since the route group is creating a new hierarchy in the
tree and defines its own layout, if the route group layout doesn't
specify a default, then the not found behavior seems correct.

To fix unexpected not-found behavior in this case, you should specify a
default at the same level as the layout where the missing slot(s) might
be rendered.

Closes NEXT-2565

packages/next/src/build/webpack/loaders/next-app-loader.ts

@@ -29,7 +29,6 @@ import {
   PAGE_SEGMENT_KEY,
 } from '../../../shared/lib/segment'
 import { getFilesInDir } from '../../../lib/get-files-in-dir'
-import { normalizeAppPath } from '../../../shared/lib/router/utils/app-paths'
 import type { PageExtensions } from '../../page-extensions-type'
 import { PARALLEL_ROUTE_DEFAULT_PATH } from '../../../client/components/parallel-route-default'
 
@@ -450,22 +449,12 @@ async function createTreeCodeFromPath(
           adjacentParallelSegment === 'children'
             ? ''
             : `/${adjacentParallelSegment}`
-        let defaultPath = await resolver(
-          `${appDirPrefix}${segmentPath}${actualSegment}/default`
-        )
 
-        if (!defaultPath) {
-          // no default was found at this segment. Check if the normalized segment resolves a default
-          // for example: /(level1)/(level2)/default doesn't exist, but /default does
-          const normalizedDefault = await resolver(
-            `${appDirPrefix}${normalizeAppPath(
-              segmentPath
-            )}/${actualSegment}/default`
-          )
-
-          // if a default is found, use that. Otherwise use the fallback, which will trigger a `notFound()`
-          defaultPath = normalizedDefault ?? PARALLEL_ROUTE_DEFAULT_PATH
-        }
+        // if a default is found, use that. Otherwise use the fallback, which will trigger a `notFound()`
+        const defaultPath =
+          (await resolver(
+            `${appDirPrefix}${segmentPath}${actualSegment}/default`
+          )) ?? PARALLEL_ROUTE_DEFAULT_PATH
 
         nestedCollectedAsyncImports.push(defaultPath)
         props[normalizeParallelKey(adjacentParallelSegment)] = `[

test/turbopack-tests-manifest.json

@@ -3566,18 +3566,6 @@
     "flakey": [],
     "runtimeError": false
   },
-  "test/e2e/app-dir/interception-route-groups/interception-route-groups.test.ts": {
-    "passed": [
-      "interception route groups (no default) should use the default fallback (a 404) if there is no custom default page"
-    ],
-    "failed": [
-      "interception route groups (with default) should render the root default when a route group doesn't have a default",
-      "interception route groups (with default) should work when nested a level deeper"
-    ],
-    "pending": [],
-    "flakey": [],
-    "runtimeError": false
-  },
   "test/e2e/app-dir/interception-route-prefetch-cache/interception-route-prefetch-cache.test.ts": {
     "passed": [
       "interception-route-prefetch-cache runtime = edge should render the correct interception when two distinct layouts share the same path structure",