fix(build): improve static path generation performance and fix parameter collisions

- Replace O(n²) parameter deduplication with O(n) Map-based approach
- Fix parameter value collisions by adding type prefixes (A: for arrays, S: for strings, U: for undefined)
- Rewrite assignErrorIfEmpty to use Trie data structure for efficient route analysis
- Add comprehensive test coverage for edge cases including collisions and empty inputs
- Sort route parameter keys for consistent Map iteration order

Author: wyattjoh

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

@@ -110,6 +110,58 @@ describe('assignErrorIfEmpty', () => {
     expect(prerenderedRoutes[3].throwOnEmptyStaticShell).toBe(true)
     expect(prerenderedRoutes[4].throwOnEmptyStaticShell).toBe(false)
   })
+
+  it('should handle parameter value collisions', () => {
+    const params = [{ slug: ['foo', 'bar'] }, { slug: 'foo,bar' }]
+
+    const unique = filterUniqueRootParamsCombinations(['slug'], params)
+
+    expect(unique).toEqual([{ slug: ['foo', 'bar'] }, { slug: 'foo,bar' }])
+  })
+
+  it('should handle multiple routes at the same trie node', () => {
+    const prerenderedRoutes: PrerenderedRoute[] = [
+      {
+        params: { id: '1' },
+        pathname: '/1/[name]',
+        encodedPathname: '/1/[name]',
+        fallbackRouteParams: ['name'],
+        fallbackMode: FallbackMode.NOT_FOUND,
+        fallbackRootParams: [],
+        throwOnEmptyStaticShell: true,
+      },
+      {
+        params: { id: '1' },
+        pathname: '/1/[name]/[extra]',
+        encodedPathname: '/1/[name]/[extra]',
+        fallbackRouteParams: ['name', 'extra'],
+        fallbackMode: FallbackMode.NOT_FOUND,
+        fallbackRootParams: [],
+        throwOnEmptyStaticShell: true,
+      },
+      {
+        params: { id: '1', name: 'test' },
+        pathname: '/1/test',
+        encodedPathname: '/1/test',
+        fallbackRouteParams: [],
+        fallbackMode: FallbackMode.NOT_FOUND,
+        fallbackRootParams: [],
+        throwOnEmptyStaticShell: true,
+      },
+    ]
+
+    assignErrorIfEmpty(prerenderedRoutes, ['id', 'name', 'extra'])
+
+    expect(prerenderedRoutes[0].throwOnEmptyStaticShell).toBe(false)
+    expect(prerenderedRoutes[1].throwOnEmptyStaticShell).toBe(false)
+    expect(prerenderedRoutes[2].throwOnEmptyStaticShell).toBe(true)
+  })
+
+  it('should handle empty input', () => {
+    const prerenderedRoutes: PrerenderedRoute[] = []
+    assignErrorIfEmpty(prerenderedRoutes, [])
+    expect(prerenderedRoutes).toEqual([])
+  })
 })
 
 describe('filterUniqueParams', () => {
@@ -154,4 +206,23 @@ describe('filterUniqueRootParamsCombinations', () => {
 
     expect(unique).toEqual([{ id: '1' }, { id: '2' }])
   })
+
+  it('should handle multiple root parameters', () => {
+    const params = [
+      { lang: 'en', region: 'US', page: 'home' },
+      { lang: 'en', region: 'US', page: 'about' },
+      { lang: 'fr', region: 'CA', page: 'home' },
+      { lang: 'fr', region: 'CA', page: 'about' },
+    ]
+
+    const unique = filterUniqueRootParamsCombinations(
+      ['lang', 'region'],
+      params
+    )
+
+    expect(unique).toEqual([
+      { lang: 'en', region: 'US' },
+      { lang: 'fr', region: 'CA' },
+    ])
+  })
 })