fix: correct compiler plugin order, only handle createMiddleware in a …

e2e/react-start/server-functions/src/routeTree.gen.ts

@@ -12,6 +12,7 @@ import { Route as rootRouteImport } from './routes/__root'
 import { Route as SubmitPostFormdataRouteImport } from './routes/submit-post-formdata'
 import { Route as StatusRouteImport } from './routes/status'
 import { Route as ServerOnlyFnRouteImport } from './routes/server-only-fn'
+import { Route as ServerFnInClientOnlyFnRouteImport } from './routes/server-fn-in-client-only-fn'
 import { Route as SerializeFormDataRouteImport } from './routes/serialize-form-data'
 import { Route as ReturnNullRouteImport } from './routes/return-null'
 import { Route as RawResponseRouteImport } from './routes/raw-response'
@@ -55,6 +56,11 @@ const ServerOnlyFnRoute = ServerOnlyFnRouteImport.update({
   path: '/server-only-fn',
   getParentRoute: () => rootRouteImport,
 } as any)
+const ServerFnInClientOnlyFnRoute = ServerFnInClientOnlyFnRouteImport.update({
+  id: '/server-fn-in-client-only-fn',
+  path: '/server-fn-in-client-only-fn',
+  getParentRoute: () => rootRouteImport,
+} as any)
 const SerializeFormDataRoute = SerializeFormDataRouteImport.update({
   id: '/serialize-form-data',
   path: '/serialize-form-data',
@@ -206,6 +212,7 @@ export interface FileRoutesByFullPath {
   '/raw-response': typeof RawResponseRoute
   '/return-null': typeof ReturnNullRoute
   '/serialize-form-data': typeof SerializeFormDataRoute
+  '/server-fn-in-client-only-fn': typeof ServerFnInClientOnlyFnRoute
   '/server-only-fn': typeof ServerOnlyFnRoute
   '/status': typeof StatusRoute
   '/submit-post-formdata': typeof SubmitPostFormdataRoute
@@ -238,6 +245,7 @@ export interface FileRoutesByTo {
   '/raw-response': typeof RawResponseRoute
   '/return-null': typeof ReturnNullRoute
   '/serialize-form-data': typeof SerializeFormDataRoute
+  '/server-fn-in-client-only-fn': typeof ServerFnInClientOnlyFnRoute
   '/server-only-fn': typeof ServerOnlyFnRoute
   '/status': typeof StatusRoute
   '/submit-post-formdata': typeof SubmitPostFormdataRoute
@@ -271,6 +279,7 @@ export interface FileRoutesById {
   '/raw-response': typeof RawResponseRoute
   '/return-null': typeof ReturnNullRoute
   '/serialize-form-data': typeof SerializeFormDataRoute
+  '/server-fn-in-client-only-fn': typeof ServerFnInClientOnlyFnRoute
   '/server-only-fn': typeof ServerOnlyFnRoute
   '/status': typeof StatusRoute
   '/submit-post-formdata': typeof SubmitPostFormdataRoute
@@ -305,6 +314,7 @@ export interface FileRouteTypes {
     | '/raw-response'
     | '/return-null'
     | '/serialize-form-data'
+    | '/server-fn-in-client-only-fn'
     | '/server-only-fn'
     | '/status'
     | '/submit-post-formdata'
@@ -337,6 +347,7 @@ export interface FileRouteTypes {
     | '/raw-response'
     | '/return-null'
     | '/serialize-form-data'
+    | '/server-fn-in-client-only-fn'
     | '/server-only-fn'
     | '/status'
     | '/submit-post-formdata'
@@ -369,6 +380,7 @@ export interface FileRouteTypes {
     | '/raw-response'
     | '/return-null'
     | '/serialize-form-data'
+    | '/server-fn-in-client-only-fn'
     | '/server-only-fn'
     | '/status'
     | '/submit-post-formdata'
@@ -402,6 +414,7 @@ export interface RootRouteChildren {
   RawResponseRoute: typeof RawResponseRoute
   ReturnNullRoute: typeof ReturnNullRoute
   SerializeFormDataRoute: typeof SerializeFormDataRoute
+  ServerFnInClientOnlyFnRoute: typeof ServerFnInClientOnlyFnRoute
   ServerOnlyFnRoute: typeof ServerOnlyFnRoute
   StatusRoute: typeof StatusRoute
   SubmitPostFormdataRoute: typeof SubmitPostFormdataRoute
@@ -446,6 +459,13 @@ declare module '@tanstack/react-router' {
       preLoaderRoute: typeof ServerOnlyFnRouteImport
       parentRoute: typeof rootRouteImport
     }
+    '/server-fn-in-client-only-fn': {
+      id: '/server-fn-in-client-only-fn'
+      path: '/server-fn-in-client-only-fn'
+      fullPath: '/server-fn-in-client-only-fn'
+      preLoaderRoute: typeof ServerFnInClientOnlyFnRouteImport
+      parentRoute: typeof rootRouteImport
+    }
     '/serialize-form-data': {
       id: '/serialize-form-data'
       path: '/serialize-form-data'
@@ -650,6 +670,7 @@ const rootRouteChildren: RootRouteChildren = {
   RawResponseRoute: RawResponseRoute,
   ReturnNullRoute: ReturnNullRoute,
   SerializeFormDataRoute: SerializeFormDataRoute,
+  ServerFnInClientOnlyFnRoute: ServerFnInClientOnlyFnRoute,
   ServerOnlyFnRoute: ServerOnlyFnRoute,
   StatusRoute: StatusRoute,
   SubmitPostFormdataRoute: SubmitPostFormdataRoute,

e2e/react-start/server-functions/src/routes/server-fn-in-client-only-fn.tsx

@@ -0,0 +1,63 @@
+import { createFileRoute } from '@tanstack/react-router'
+import { createClientOnlyFn, createServerFn } from '@tanstack/react-start'
+import { useState } from 'react'
+
+// Server function that should be callable from client-only function
+const serverFn = createServerFn().handler(() => {
+  return 'server function executed successfully'
+})
+
+// Client-only function that calls the server function
+// This scenario currently fails due to compilation order issues:
+// 1. createClientOnlyFn is processed first, removing the serverFn reference on server
+// 2. Dead code elimination removes the serverFn entirely
+// 3. The server function is never registered, causing runtime errors
+const clientOnlyFnThatCallsServerFn = createClientOnlyFn(async () => {
+  const result = await serverFn()
+  return 'client-only fn received: ' + result
+})
+
+export const Route = createFileRoute('/server-fn-in-client-only-fn')({
+  component: RouteComponent,
+})
+
+function RouteComponent() {
+  const [result, setResult] = useState<string | null>(null)
+  const [error, setError] = useState<string | null>(null)
+
+  async function handleClick() {
+    try {
+      const res = await clientOnlyFnThatCallsServerFn()
+      setResult(res)
+      setError(null)
+    } catch (e) {
+      setResult(null)
+      setError(e instanceof Error ? e.message : String(e))
+    }
+  }
+
+  return (
+    <div>
+      <h1>Server Function in Client-Only Function Test</h1>
+      <p>
+        This test verifies that a server function can be called from inside a
+        createClientOnlyFn.
+      </p>
+      <button
+        onClick={handleClick}
+        data-testid="test-server-fn-in-client-only-fn-btn"
+      >
+        Call client-only function that calls server function
+      </button>
+      <pre data-testid="expected-result">
+        client-only fn received: server function executed successfully
+      </pre>
+      {result && (
+        <pre data-testid="server-fn-in-client-only-fn-result">{result}</pre>
+      )}
+      {error && (
+        <pre data-testid="server-fn-in-client-only-fn-error">{error}</pre>
+      )}
+    </div>
+  )
+}

e2e/react-start/server-functions/tests/server-functions.spec.ts

@@ -543,40 +543,3 @@ test('redirect in server function called in query during SSR', async ({
   await expect(page.getByTestId('redirect-target-ssr')).toBeVisible()
   expect(page.url()).toContain('/redirect-test-ssr/target')
 })
-
-test('server function called only from server (not client) works correctly', async ({
-  page,
-}) => {
-  await page.goto('/server-only-fn')
-
-  await page.waitForLoadState('networkidle')
-
-  const expected =
-    (await page.getByTestId('expected-server-only-fn-result').textContent()) ||
-    ''
-  expect(expected).not.toBe('')
-
-  await page.getByTestId('test-server-only-fn-btn').click()
-  await page.waitForLoadState('networkidle')
-
-  await expect(page.getByTestId('server-only-fn-result')).toContainText(
-    expected,
-  )
-})
-
-test.use({
-  whitelistErrors: [
-    /Failed to load resource: the server responded with a status of 500/,
-  ],
-})
-test('server function called only from server (not client) cannot be called from the client', async ({
-  page,
-}) => {
-  await page.goto('/server-only-fn')
-  await page.waitForLoadState('networkidle')
-
-  await page.getByTestId('call-server-fn-from-client-btn').click()
-  await expect(
-    page.getByTestId('call-server-fn-from-client-result'),
-  ).toContainText('error')
-})

packages/start-plugin-core/src/create-server-fn-plugin/handleCreateMiddleware.ts

@@ -8,14 +8,11 @@ export function handleCreateMiddleware(
     env: 'client' | 'server'
   },
 ) {
+  if (opts.env === 'server') {
+    throw new Error('handleCreateMiddleware should not be called on the server')
+  }
   const rootCallExpression = getRootCallExpression(path)
 
-  // if (debug)
-  //   console.info(
-  //     'Handling createMiddleware call expression:',
-  //     rootCallExpression.toString(),
-  //   )
-
   const callExpressionPaths = {
     middleware: null as babel.NodePath<t.CallExpression> | null,
     inputValidator: null as babel.NodePath<t.CallExpression> | null,
@@ -51,28 +48,20 @@ export function handleCreateMiddleware(
       )
     }
 
-    // If we're on the client, remove the validator call expression
-    if (opts.env === 'client') {
-      if (
-        t.isMemberExpression(callExpressionPaths.inputValidator.node.callee)
-      ) {
-        callExpressionPaths.inputValidator.replaceWith(
-          callExpressionPaths.inputValidator.node.callee.object,
-        )
-      }
+    // remove the validator call expression
+    if (t.isMemberExpression(callExpressionPaths.inputValidator.node.callee)) {
+      callExpressionPaths.inputValidator.replaceWith(
+        callExpressionPaths.inputValidator.node.callee.object,
+      )
     }
   }
 
   const serverFnPath = callExpressionPaths.server?.get(
     'arguments.0',
   ) as babel.NodePath<any>
 
-  if (
-    callExpressionPaths.server &&
-    serverFnPath.node &&
-    opts.env === 'client'
-  ) {
-    // If we're on the client, remove the server call expression
+  if (callExpressionPaths.server && serverFnPath.node) {
+    // remove the server call expression
     if (t.isMemberExpression(callExpressionPaths.server.node.callee)) {
       callExpressionPaths.server.replaceWith(
         callExpressionPaths.server.node.callee.object,

packages/start-plugin-core/src/plugin.ts

@@ -385,14 +385,17 @@ export function TanStackStartVitePluginCore(
       },
     },
     tanStackStartRouter(startPluginOpts, getConfig, corePluginOpts),
-    // N.B. TanStackStartCompilerPlugin must be before the TanStackServerFnPlugin
-    startCompilerPlugin({ framework: corePluginOpts.framework, environments }),
+    // N.B. Server function plugins must run BEFORE startCompilerPlugin because:
+    // 1. createServerFnPlugin transforms createServerFn().handler() to inject 'use server' directive
+    // 2. TanStackServerFnPlugin extracts 'use server' functions and registers them in the manifest
+    // 3. startCompilerPlugin handles createClientOnlyFn/createServerOnlyFn and runs DCE
+    // If startCompilerPlugin runs first, DCE may remove server function code before it can be registered
+    // (e.g., when a server function is only referenced inside a createClientOnlyFn callback)
     createServerFnPlugin({
       framework: corePluginOpts.framework,
       directive,
       environments,
     }),
-
     TanStackServerFnPlugin({
       // This is the ID that will be available to look up and import
       // our server function manifest and resolve its module
@@ -428,6 +431,7 @@ export function TanStackStartVitePluginCore(
         envName: serverFnProviderEnv,
       },
     }),
+    startCompilerPlugin({ framework: corePluginOpts.framework, environments }),
     loadEnvPlugin(),
     startManifestPlugin({
       getClientBundle: () => getBundle(VITE_ENVIRONMENT_NAMES.client),

packages/start-plugin-core/src/start-compiler-plugin/compilers.ts

@@ -6,7 +6,6 @@ import {
   findReferencedIdentifiers,
 } from 'babel-dead-code-elimination'
 import { generateFromAst, parseAst } from '@tanstack/router-utils'
-import { handleCreateMiddleware } from '../create-server-fn-plugin/handleCreateMiddleware'
 import { transformFuncs } from './constants'
 import { handleCreateIsomorphicFnCallExpression } from './isomorphicFn'
 import {
@@ -41,16 +40,6 @@ export function compileStartOutputFactory(
       },
     }
 
-    // createMiddleware only performs modifications in the client environment
-    // so we can avoid executing this on the server
-    if (opts.env === 'client') {
-      identifiers.createMiddleware = {
-        name: 'createMiddleware',
-        handleCallExpression: handleCreateMiddleware,
-        paths: [],
-      }
-    }
-
     const ast = parseAst(opts)
 
     const doDce = opts.dce ?? true

packages/start-plugin-core/src/start-compiler-plugin/constants.ts

@@ -2,5 +2,4 @@ export const transformFuncs = [
   'createServerOnlyFn',
   'createClientOnlyFn',
   'createIsomorphicFn',
-  'createMiddleware',
 ] as const

packages/start-plugin-core/tests/createMiddleware-create-server-fn-plugin/createMiddleware.test.ts

@@ -50,15 +50,13 @@ describe('createMiddleware compiles correctly', async () => {
     )
     const code = file.toString()
 
-    test.each(['client', 'server'] as const)(
-      `should compile for ${filename} %s`,
-      async (env) => {
-        const result = await compile({ env, code, id: filename })
+    // Note: Middleware compilation only happens on the client
+    test(`should compile for ${filename} client`, async () => {
+      const result = await compile({ env: 'client', code, id: filename })
 
-        await expect(result!.code).toMatchFileSnapshot(
-          `./snapshots/${env}/${filename}`,
-        )
-      },
-    )
+      await expect(result!.code).toMatchFileSnapshot(
+        `./snapshots/client/${filename}`,
+      )
+    })
   })
 })

packages/start-plugin-core/tests/createMiddleware-start-compiler-plugin/snapshots/client/create-function-middleware.ts → packages/start-plugin-core/tests/createMiddleware-create-server-fn-plugin/snapshots/client/create-function-middleware.ts

@@ -1,5 +1,4 @@
 import { createMiddleware } from '@tanstack/react-start';
-import { foo } from '@some/lib';
 export const fnMw = createMiddleware({
   type: 'function'
 }).client(() => {

packages/start-plugin-core/tests/createMiddleware-create-server-fn-plugin/snapshots/client/createMiddlewareDestructured.tsx

@@ -0,0 +1,13 @@
+import { createMiddleware } from '@tanstack/react-start';
+export const withUseServer = createMiddleware({
+  id: 'test'
+});
+export const withoutUseServer = createMiddleware({
+  id: 'test'
+});
+export const withVariable = createMiddleware({
+  id: 'test'
+});
+export const withZodValidator = createMiddleware({
+  id: 'test'
+});

packages/start-plugin-core/tests/createMiddleware-create-server-fn-plugin/snapshots/client/createMiddlewareDestructuredRename.tsx

@@ -0,0 +1,13 @@
+import { createMiddleware as middlewareFn } from '@tanstack/react-start';
+export const withUseServer = middlewareFn({
+  id: 'test'
+});
+export const withoutUseServer = middlewareFn({
+  id: 'test'
+});
+export const withVariable = middlewareFn({
+  id: 'test'
+});
+export const withZodValidator = middlewareFn({
+  id: 'test'
+});

packages/start-plugin-core/tests/createMiddleware-create-server-fn-plugin/snapshots/client/createMiddlewareStarImport.tsx

@@ -0,0 +1,13 @@
+import * as TanStackStart from '@tanstack/react-start';
+export const withUseServer = TanStackStart.createMiddleware({
+  id: 'test'
+});
+export const withoutUseServer = TanStackStart.createMiddleware({
+  id: 'test'
+});
+export const withVariable = TanStackStart.createMiddleware({
+  id: 'test'
+});
+export const withZodValidator = TanStackStart.createMiddleware({
+  id: 'test'
+});

packages/start-plugin-core/tests/createMiddleware-start-compiler-plugin/snapshots/client/createMiddlewareValidator.tsx → packages/start-plugin-core/tests/createMiddleware-create-server-fn-plugin/snapshots/client/createMiddlewareValidator.tsx

@@ -1,5 +1,4 @@
 import { createMiddleware } from '@tanstack/react-start';
-import { z } from 'zod';
 export const withUseServer = createMiddleware({
   id: 'test'
 });