This is because Vitest internally sets esbuild option while @vitejs/plugin-react-oxc automatically sets oxc option.

I'd imagine this causes a different behavior on rolldown-vite, but probably minor one. We should use equivalent oxc option instead when rolldown-vite is detected. But, I realized that this would technically cause reverse breaking behavior. If users or plugins currently relies on esbuild option but Vitest automatically sets oxc, then users/plugins esbuild is going to be completely ignored 🤔

Note that when both Vitest and users only uses esbuild config, then they should be merged properly and then rolldown-vite automatically converts esbuild option into oxc option equivalent.

(Btw, @vitejs/plugin-react-oxc will be incorporated into @vitejs/plugin-react directly soon https://github.com/vitejs/vite-plugin-react/releases/tag/plugin-react%405.0.0-beta.0, but the warning will be likely same unless Vitest addresses this.)