fix: better error message in router generator (#4538)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

Author: schiller-manuel

packages/router-generator/src/transform/default-transform-plugin.ts

@@ -4,9 +4,10 @@ import type { TransformImportsConfig, TransformPlugin } from './types'
 
 const b = types.builders
 
+const EXPORT_NAME = 'Route'
 export const defaultTransformPlugin: TransformPlugin = {
   name: 'default-transform',
-  exportName: 'Route',
+  exportName: EXPORT_NAME,
   imports: (ctx) => {
     const imports: TransformImportsConfig = {}
     const targetModule = `@tanstack/${ctx.target}-router`
@@ -87,7 +88,9 @@ export const defaultTransformPlugin: TransformPlugin = {
         }
       }
       if (identifier === undefined) {
-        throw new Error(`expected identifier to be present`)
+        throw new Error(
+          `expected identifier to be present in ${ctx.routeId} for export ${EXPORT_NAME}`,
+        )
       }
       if (identifier.name === 'createFileRoute' && ctx.lazy) {
         identifier.name = 'createLazyFileRoute'