[Compiler Bug]: healthcheck do not check next.js StrictMode

[coleea]

What kind of issue is this?

• React Compiler core (the JS output is incorrect, or your app works incorrectly after optimization)
• babel-plugin-react-compiler (build issue installing or using the Babel plugin)
• eslint-plugin-react-compiler (build issue installing or using the eslint plugin)
• react-compiler-healthcheck (build issue installing or using the healthcheck script)

Link to repro

https://github.com/coleea/bug-report-next15-server-action

Repro steps

just run command npx react-compiler-healthcheck@latest.
then, react-compiler-healthcheck does not check StrictMode even though Next.js is actually StrictMode.

Next.js is StrictMode by default under these two conditions are met

1. Next.js version 13.4+
2. App router

You can check this : https://rc.nextjs.org/docs/app/api-reference/next-config-js/reactStrictMode

So, It needs extra three steps to check whether StrictMode or Not.

1. check package.json if Next.js version is over 13.4 or not.
2. If so, Check if reactStrictMode: false is not set.
3. check if project is App-Router-based.

If three conditions are met, this project is based on StrictMode even though reactStrictMode: true is not set on next.config.mjs file.

How often does this bug happen?

Every time

What version of React are you using?

19.0.0-rc.0

[coleea]

If my argument is not wrong, I am willing to implement it, so please reply

[gsathya]

This is already fixed: #29167

This will roll out once we make a new release of the healthcheck script

[coleea]

@gsathya The PR you mentioned is just check whether reactStrictMode: true
option exists in next.config.mjs or not. that's not enough.
I wrote this issue after reading this PR.

[coleea]

There are 6 cases

1. App router + reactStrictMode: true => strict mode. PR cover this case.
2. App router + reactStrictMode: false => non-strict mode. PR cover this case.
3. App router + reactStrictMode option is not set => strict mode. PR does not cover this case.
4. Page router + reactStrictMode: true => strict mode. PR cover this case.
5. Page router + reactStrictMode: false => non-strict mode. PR cover this case.
6. Page router + reactStrictMode option is not set => non-strict mode. PR cover this case.

Please check the 3rd case to determine whether #29167 covers this or not.

[gsathya]

Ah good point, I'll re-open this.