[backport] fix: avoid importing types that will be unused (#82856) (#83026)

Author: bgub

packages/next/src/server/lib/router-utils/typegen.ts

@@ -579,7 +579,23 @@ export function generateValidatorFile(
   }
 
   // Build import statement based on what's actually needed
-  const routeImports = ['AppRoutes', 'LayoutRoutes', 'ParamMap']
+  const routeImports = []
+
+  // Only import AppRoutes if there are app pages
+  if (appPageValidations) {
+    routeImports.push('AppRoutes')
+  }
+
+  // Only import LayoutRoutes if there are layouts
+  if (layoutValidations) {
+    routeImports.push('LayoutRoutes')
+  }
+
+  // Only import ParamMap if there are routes that use it
+  if (appPageValidations || layoutValidations || appRouteHandlerValidations) {
+    routeImports.push('ParamMap')
+  }
+
   if (hasAppRouteHandlers) {
     routeImports.push('AppRouteHandlerRoutes')
   }
@@ -593,13 +609,18 @@ export function generateValidatorFile(
     ? "import type { NextRequest } from 'next/server.js'\n"
     : ''
 
+  // Only import metadata types if there are App Router pages or layouts that might use them
+  const metadataImport =
+    appPageValidations || layoutValidations
+      ? 'import type { ResolvingMetadata, ResolvingViewport } from "next/dist/lib/metadata/types/metadata-interface.js"\n'
+      : ''
+
   return `// This file is generated automatically by Next.js
 // Do not edit this file manually
 // This file validates that all pages and layouts export the correct types
 
 ${routeImportStatement}
-import type { ResolvingMetadata, ResolvingViewport } from "next/dist/lib/metadata/types/metadata-interface.js"
-${nextRequestImport}
+${metadataImport}${nextRequestImport}
 ${typeDefinitions}
 ${appPageValidations}