feat(config): support next.config reactCompiler option

[314systems]

Summary

Adds support for the stable Next.js reactCompiler config option:

import type { NextConfig } from "next";

const nextConfig: NextConfig = {
  reactCompiler: true,
};

export default nextConfig;

The object form is also supported: reactCompiler: { compilationMode: "annotation", panicThreshold: "critical_errors" }.

Closes #2674

Implementation

Mirrors Next.js behavior from packages/next/src/build/get-babel-loader-config.ts:

• runs the compiler on client transforms only
• requires babel-plugin-react-compiler and reports a clear install error when missing
• pins target: "18" when React 18 is installed
• enables anonymous-function names in development
• runs the compiler before user-supplied Babel plugins

Both supported plugin-react generations are handled:

• @vitejs/plugin-react v5 uses its function-form babel option
• @vitejs/plugin-react v6 uses @rolldown/plugin-babel with a lazy, client-only preset; this path additionally requires @rolldown/plugin-babel

The v6 path also pre-optimizes react/compiler-runtime or react-compiler-runtime, depending on the detected React target. With vinext({ react: false }), vinext warns that the compiler must be configured in the user's own React plugin setup.

Verification

• config normalization and compiler helper unit tests
• plugin-react auto-registration integration test
• isolated real client transform using @rolldown/plugin-babel@0.2.3 and babel-plugin-react-compiler@1.0.0; output contains react.memo_cache_sentinel
• verified the matching compiler runtime is included in client optimizeDeps.include

Documentation

The README configuration table documents the accepted values, dependencies, client-only behavior, and react: false caveat.

[314systems]

I re-verified this against the installed @vitejs/plugin-react v6 implementation and found that the initial commit used the removed v5 babel option, so v6 silently ignored the compiler configuration.

Fixed in 88cfbf4:

• plugin-react v6 now uses @rolldown/plugin-babel with a lazy, client-only React Compiler preset
• plugin-react v5 retains the function-form babel callback path
• the matching compiler runtime is added to client optimizeDeps.include
• the README and missing-dependency error now mention the additional @rolldown/plugin-babel requirement for v6

I also ran an isolated real transform with @rolldown/plugin-babel@0.2.3 and babel-plugin-react-compiler@1.0.0 through vinext({ nextConfig: { reactCompiler: true } }). The transformed client module contains react.memo_cache_sentinel, and react/compiler-runtime is present in the client optimizer includes.