Add warn message if no instrument file found

Author: nicohrubec

packages/tanstackstart-react/src/vite/copyInstrumentationFile.ts

@@ -49,6 +49,7 @@ export function makeCopyInstrumentationFilePlugin(): Plugin {
           );
         });
       }
+
     },
 
     async closeBundle() {
@@ -61,7 +62,13 @@ export function makeCopyInstrumentationFilePlugin(): Plugin {
       try {
         await fs.promises.access(instrumentationSource, fs.constants.F_OK);
       } catch {
-        // No instrumentation file found — nothing to copy
+        consoleSandbox(() => {
+          // eslint-disable-next-line no-console
+          console.warn(
+            '[Sentry TanStack Start] No instrument.server.mjs file found in project root. ' +
+              'The Sentry instrumentation file will not be copied to the build output.',
+          );
+        });
         return;
       }
 

packages/tanstackstart-react/test/vite/copyInstrumentationFile.test.ts

@@ -196,7 +196,7 @@ describe('makeCopyInstrumentationFilePlugin()', () => {
       warnSpy.mockRestore();
     });
 
-    it('does nothing when instrumentation file does not exist', async () => {
+    it('warns and does not copy when instrumentation file does not exist', async () => {
       const resolvedConfig = {
         root: '/project',
         plugins: [{ name: 'nitro' }],
@@ -217,10 +217,18 @@ describe('makeCopyInstrumentationFilePlugin()', () => {
 
       vi.mocked(fs.promises.access).mockRejectedValueOnce(new Error('ENOENT'));
 
+      const warnSpy = vi.spyOn(console, 'warn').mockImplementation(() => {});
+
       await (plugin.closeBundle as AnyFunction)();
 
       expect(fs.promises.access).toHaveBeenCalled();
       expect(fs.promises.copyFile).not.toHaveBeenCalled();
+      expect(warnSpy).toHaveBeenCalledWith(
+        '[Sentry TanStack Start] No instrument.server.mjs file found in project root. ' +
+          'The Sentry instrumentation file will not be copied to the build output.',
+      );
+
+      warnSpy.mockRestore();
     });
 
     it('logs a warning when copy fails', async () => {