test(build): add test cases for route shell examples

- Add test for blog/[slug] shell route with concrete posts
- Add test for [id]/[...slug] catch-all route pattern
- Add test for multiple shell levels with nested parameters
- Add test for routes at same trie node with different fallback lengths

These tests validate the behavior described in the updated comments
and ensure proper shell route detection in the Trie structure.

Author: wyattjoh

packages/next/src/build/static-paths/app.test.ts

@@ -162,6 +162,164 @@ describe('assignErrorIfEmpty', () => {
     assignErrorIfEmpty(prerenderedRoutes, [])
     expect(prerenderedRoutes).toEqual([])
   })
+
+  it('should handle blog/[slug] not throwing when concrete routes exist (from docs example)', () => {
+    const prerenderedRoutes: PrerenderedRoute[] = [
+      {
+        params: {},
+        pathname: '/blog/[slug]',
+        encodedPathname: '/blog/[slug]',
+        fallbackRouteParams: ['slug'],
+        fallbackMode: FallbackMode.NOT_FOUND,
+        fallbackRootParams: [],
+        throwOnEmptyStaticShell: true,
+      },
+      {
+        params: { slug: 'first-post' },
+        pathname: '/blog/first-post',
+        encodedPathname: '/blog/first-post',
+        fallbackRouteParams: [],
+        fallbackMode: FallbackMode.NOT_FOUND,
+        fallbackRootParams: [],
+        throwOnEmptyStaticShell: true,
+      },
+      {
+        params: { slug: 'second-post' },
+        pathname: '/blog/second-post',
+        encodedPathname: '/blog/second-post',
+        fallbackRouteParams: [],
+        fallbackMode: FallbackMode.NOT_FOUND,
+        fallbackRootParams: [],
+        throwOnEmptyStaticShell: true,
+      },
+    ]
+
+    assignErrorIfEmpty(prerenderedRoutes, ['slug'])
+
+    expect(prerenderedRoutes[0].throwOnEmptyStaticShell).toBe(false) // Should not throw - has concrete children
+    expect(prerenderedRoutes[1].throwOnEmptyStaticShell).toBe(true) // Should throw - concrete route
+    expect(prerenderedRoutes[2].throwOnEmptyStaticShell).toBe(true) // Should throw - concrete route
+  })
+
+  it('should handle catch-all routes with different fallback parameter counts (from docs example)', () => {
+    const prerenderedRoutes: PrerenderedRoute[] = [
+      {
+        params: {},
+        pathname: '/[id]/[...slug]',
+        encodedPathname: '/[id]/[...slug]',
+        fallbackRouteParams: ['id', 'slug'],
+        fallbackMode: FallbackMode.NOT_FOUND,
+        fallbackRootParams: [],
+        throwOnEmptyStaticShell: true,
+      },
+      {
+        params: { id: '1234' },
+        pathname: '/1234/[...slug]',
+        encodedPathname: '/1234/[...slug]',
+        fallbackRouteParams: ['slug'],
+        fallbackMode: FallbackMode.NOT_FOUND,
+        fallbackRootParams: [],
+        throwOnEmptyStaticShell: true,
+      },
+      {
+        params: { id: '1234', slug: ['about', 'us'] },
+        pathname: '/1234/about/us',
+        encodedPathname: '/1234/about/us',
+        fallbackRouteParams: [],
+        fallbackMode: FallbackMode.NOT_FOUND,
+        fallbackRootParams: [],
+        throwOnEmptyStaticShell: true,
+      },
+    ]
+
+    assignErrorIfEmpty(prerenderedRoutes, ['id', 'slug'])
+
+    expect(prerenderedRoutes[0].throwOnEmptyStaticShell).toBe(false) // Should not throw - has children
+    expect(prerenderedRoutes[1].throwOnEmptyStaticShell).toBe(false) // Should not throw - has children
+    expect(prerenderedRoutes[2].throwOnEmptyStaticShell).toBe(true) // Should throw - concrete route
+  })
+
+  it('should handle nested routes with multiple parameter depths', () => {
+    const prerenderedRoutes: PrerenderedRoute[] = [
+      {
+        params: {},
+        pathname: '/[category]/[subcategory]/[item]',
+        encodedPathname: '/[category]/[subcategory]/[item]',
+        fallbackRouteParams: ['category', 'subcategory', 'item'],
+        fallbackMode: FallbackMode.NOT_FOUND,
+        fallbackRootParams: [],
+        throwOnEmptyStaticShell: true,
+      },
+      {
+        params: { category: 'electronics' },
+        pathname: '/electronics/[subcategory]/[item]',
+        encodedPathname: '/electronics/[subcategory]/[item]',
+        fallbackRouteParams: ['subcategory', 'item'],
+        fallbackMode: FallbackMode.NOT_FOUND,
+        fallbackRootParams: [],
+        throwOnEmptyStaticShell: true,
+      },
+      {
+        params: { category: 'electronics', subcategory: 'phones' },
+        pathname: '/electronics/phones/[item]',
+        encodedPathname: '/electronics/phones/[item]',
+        fallbackRouteParams: ['item'],
+        fallbackMode: FallbackMode.NOT_FOUND,
+        fallbackRootParams: [],
+        throwOnEmptyStaticShell: true,
+      },
+      {
+        params: {
+          category: 'electronics',
+          subcategory: 'phones',
+          item: 'iphone',
+        },
+        pathname: '/electronics/phones/iphone',
+        encodedPathname: '/electronics/phones/iphone',
+        fallbackRouteParams: [],
+        fallbackMode: FallbackMode.NOT_FOUND,
+        fallbackRootParams: [],
+        throwOnEmptyStaticShell: true,
+      },
+    ]
+
+    assignErrorIfEmpty(prerenderedRoutes, ['category', 'subcategory', 'item'])
+
+    // All except the last one should not throw on empty static shell
+    expect(prerenderedRoutes[0].throwOnEmptyStaticShell).toBe(false)
+    expect(prerenderedRoutes[1].throwOnEmptyStaticShell).toBe(false)
+    expect(prerenderedRoutes[2].throwOnEmptyStaticShell).toBe(false)
+    expect(prerenderedRoutes[3].throwOnEmptyStaticShell).toBe(true)
+  })
+
+  it('should handle routes at same trie node with different fallback parameter lengths', () => {
+    const prerenderedRoutes: PrerenderedRoute[] = [
+      {
+        params: { locale: 'en' },
+        pathname: '/en/[...segments]',
+        encodedPathname: '/en/[...segments]',
+        fallbackRouteParams: ['segments'],
+        fallbackMode: FallbackMode.NOT_FOUND,
+        fallbackRootParams: [],
+        throwOnEmptyStaticShell: true,
+      },
+      {
+        params: { locale: 'en' },
+        pathname: '/en',
+        encodedPathname: '/en',
+        fallbackRouteParams: [],
+        fallbackMode: FallbackMode.NOT_FOUND,
+        fallbackRootParams: [],
+        throwOnEmptyStaticShell: true,
+      },
+    ]
+
+    assignErrorIfEmpty(prerenderedRoutes, ['locale', 'segments'])
+
+    // The route with more fallback params should not throw on empty static shell
+    expect(prerenderedRoutes[0].throwOnEmptyStaticShell).toBe(false)
+    expect(prerenderedRoutes[1].throwOnEmptyStaticShell).toBe(true)
+  })
 })
 
 describe('filterUniqueParams', () => {