React Compiler broken since 15.3.1

[mondaychen]

Link to the code that reproduces this issue

https://github.com/mondaychen/next-react-compiler-reproducer

To Reproduce

1. checkout https://github.com/mondaychen/next-react-compiler-reproducer and npm i
2. npm run dev
3. visit http://localhost:3000/ with React DevTools open
4. See no component with "Memo" tag in React DevTools. Also the component is not optimized when you click the button

Current vs. Expected behavior

Current behavior see above

Expected behavior (Next.js v15.3.0 works)

You can try it with the other branch https://github.com/mondaychen/next-react-compiler-reproducer/tree/15.3.0

When you click the button, the random number does not change

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.3.0: Thu Jan  2 20:24:23 PST 2025; root:xnu-11215.81.4~3/RELEASE_ARM64_T6020
  Available memory (MB): 16384
  Available CPU cores: 12
Binaries:
  Node: 22.11.0
  npm: 10.9.0
  Yarn: N/A
  pnpm: 9.13.2
Relevant Packages:
  next: 15.3.1 // There is a newer version (15.3.2) available, upgrade recommended! 
  eslint-config-next: 15.3.2
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.8.3
Next.js Config:
  output: N/A
 ⚠ There is a newer version (15.3.2) available, upgrade recommended! 
   Please try the latest canary version (`npm install next@canary`) to confirm the issue still exists before creating a new issue.
   Read more - https://nextjs.org/docs/messages/opening-an-issue

Which area(s) are affected? (Select all that apply)

React

Which stage(s) are affected? (Select all that apply)

next dev (local)

Additional context

I've tried with 15.3.2, it has the same issue with 15.3.1

[mondaychen]

The problem still exists on v15.4.0-canary.40

[Daniel3711997]

I can confirm that, returning true from this function solves the issue:

next.js/packages/next/src/build/swc/index.ts

Line 1333 in 070d31f

export async function isReactCompilerRequired(

After this fix #78867, a new issue occurred

Something strange is happening now, sometimes the react compiler works correctly and sometimes it just flags the component as is using 'memo' in react dev tools but looking at the compiled code there is no optimization.

This also happens when running the next build command, no code optimization is found on the compiled code but the component is flagged as 'Auto memo' in react dev tools.

The problematic pull: 070d31f#diff-907b7be0cfc75bd37773e5ebc38d1deffa40861b8ac1cde92e4992e284a1ee59R1108

[mondaychen]

@Daniel3711997 in my case it does not flag the component as using "memo" in react devtools either

[Daniel3711997]

Currently i use a patch to disable the 'Run the React Compiler only on select files' until the Next.JS team figure it out. (Maybe it is helpful for someone)

Seems to be a race condition somewhere because sometimes it works and sometimes not, but somehow (for me at least) the component is flagged as 'Memo' but the optimization is missing.

next+15.3.2.patch

diff --git a/node_modules/next/dist/build/babel/loader/get-config.js b/node_modules/next/dist/build/babel/loader/get-config.js
index b716a7b..9874cfc 100644
--- a/node_modules/next/dist/build/babel/loader/get-config.js
+++ b/node_modules/next/dist/build/babel/loader/get-config.js
@@ -234,9 +234,9 @@ let babelConfigWarned = false;
         if (loaderOptions.reactCompilerExclude && loaderOptions.reactCompilerExclude(filename)) {
             return false;
         }
-        if (!await (0, _swc.isReactCompilerRequired)(filename)) {
-            return false;
-        }
+        // if (!await (0, _swc.isReactCompilerRequired)(filename)) {
+        //     return false;
+        // }
         return true;
     })();
     const reactCompilerPluginsIfEnabled = hasReactCompiler ? loaderOptions.reactCompilerPlugins ?? [] : [];

[fadomire]

Maybe it’s a potential source of issues to try and decide on behalf of the compiler which files are relevant or not?

[altyntsevlexus]

@kdy1 Hello, I saw you answering in previous Issue. Is there any news about this one? Thanks.

[github-actions]

This closed issue has been automatically locked because it had no new activity for 2 weeks. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.