From c7cfa35bbdc2adbb96269def1e66da50a6fef56a Mon Sep 17 00:00:00 2001
From: Manuel Schiller <manuel.schiller@caligano.de>
Date: Thu, 30 Oct 2025 19:01:52 +0100
Subject: [PATCH] fix: only run middleware compiler in client env

---
 .../src/start-compiler-plugin/compilers.ts    | 39 +++++++++++++------
 1 file changed, 27 insertions(+), 12 deletions(-)

diff --git a/packages/start-plugin-core/src/start-compiler-plugin/compilers.ts b/packages/start-plugin-core/src/start-compiler-plugin/compilers.ts
index f5d244e5c1a..d300fe48c97 100644
--- a/packages/start-plugin-core/src/start-compiler-plugin/compilers.ts
+++ b/packages/start-plugin-core/src/start-compiler-plugin/compilers.ts
@@ -23,7 +23,7 @@ export function compileStartOutputFactory(
   framework: CompileStartFrameworkOptions,
 ) {
   return function compileStartOutput(opts: CompileOptions): GeneratorResult {
-    const identifiers: Identifiers = {
+    const identifiers: Partial<Identifiers> = {
       createServerOnlyFn: {
         name: 'createServerOnlyFn',
         handleCallExpression: handleCreateServerOnlyFnCallExpression,
@@ -39,11 +39,16 @@ export function compileStartOutputFactory(
         handleCallExpression: handleCreateIsomorphicFnCallExpression,
         paths: [],
       },
-      createMiddleware: {
+    }
+
+    // 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)
@@ -65,7 +70,9 @@ export function compileStartOutputFactory(
               path.node.specifiers.forEach((specifier) => {
                 transformFuncs.forEach((identifierKey) => {
                   const identifier = identifiers[identifierKey]
-
+                  if (!identifier) {
+                    return
+                  }
                   if (
                     specifier.type === 'ImportSpecifier' &&
                     specifier.imported.type === 'Identifier'
@@ -84,11 +91,15 @@ export function compileStartOutputFactory(
             },
             CallExpression: (path) => {
               transformFuncs.forEach((identifierKey) => {
+                const identifier = identifiers[identifierKey]
+                if (!identifier) {
+                  return
+                }
                 // Check to see if the call expression is a call to the
                 // identifiers[identifierKey].name
                 if (
                   t.isIdentifier(path.node.callee) &&
-                  path.node.callee.name === identifiers[identifierKey].name
+                  path.node.callee.name === identifier.name
                 ) {
                   // The identifier could be a call to the original function
                   // in the source code. If this is case, we need to ignore it.
@@ -96,13 +107,13 @@ export function compileStartOutputFactory(
                   // if it is, then we can ignore it.
 
                   if (
-                    path.scope.getBinding(identifiers[identifierKey].name)?.path
-                      .node.type === 'FunctionDeclaration'
+                    path.scope.getBinding(identifier.name)?.path.node.type ===
+                    'FunctionDeclaration'
                   ) {
                     return
                   }
 
-                  return identifiers[identifierKey].paths.push(path)
+                  return identifier.paths.push(path)
                 }
 
                 // handle namespace imports like "import * as TanStackStart from '@tanstack/react-start';"
@@ -117,8 +128,8 @@ export function compileStartOutputFactory(
                       path.node.callee.property.name,
                     ].join('.')
 
-                    if (callname === identifiers[identifierKey].name) {
-                      identifiers[identifierKey].paths.push(path)
+                    if (callname === identifier.name) {
+                      identifier.paths.push(path)
                     }
                   }
                 }
@@ -129,8 +140,12 @@ export function compileStartOutputFactory(
           })
 
           transformFuncs.forEach((identifierKey) => {
-            identifiers[identifierKey].paths.forEach((path) => {
-              identifiers[identifierKey].handleCallExpression(
+            const identifier = identifiers[identifierKey]
+            if (!identifier) {
+              return
+            }
+            identifier.paths.forEach((path) => {
+              identifier.handleCallExpression(
                 path as babel.NodePath<t.CallExpression>,
                 opts,
               )