Babel plugins that read AST `loc` produce wrong positions when running after OXC

[Artur-]

Related plugins

• plugin-react

• plugin-react-swc

• plugin-rsc

Describe the bug

When a Babel plugin runs after @vitejs/plugin-react's OXC transform (using @rolldown/plugin-babel with enforce: 'post' or a custom plugin), the Babel AST loc values refer to the OXC-transformed code, not the original source. Any Babel plugin that reads loc.start.line / loc.start.column to embed source positions in the output will produce incorrect values.

This was not an issue with @vitejs/plugin-react v5 where Babel handled both JSX transform and custom plugins in a single pass — loc always pointed to the original source.

Example

We have a Babel plugin that inserts ComponentName.__debugSourceDefine = { fileName, lineNumber, columnNumber } after each React function component, using the function body's loc:

FunctionDeclaration(path, state) {
  const name = path.node.id.name;
  const loc = path.node.body.loc;  // ← wrong after OXC transform
  // inserts: Foo.__debugSourceDefine = { fileName: "...", lineNumber: loc.start.line, ... }
  path.insertAfter(createDebugInfo(name, state.file.opts.filename, loc));
}

With v5 (react({ babel: { plugins: [myPlugin] } })), loc.start.line referred to the original .tsx file. With v6, OXC transforms JSX first, changing line numbers. Babel sees the transformed code and its loc values are offset.

The dilemma — no configuration produces correct results

With enforce: 'pre' (default) — Babel runs before OXC:

• ✅ __debugSourceDefine line numbers are correct (Babel sees original source)
• ❌ OXC's jsxDEV() source info is wrong — every JSX element in the app gets shifted line numbers because Babel inserted __debugSourceDefine blocks (4+ lines each) before OXC processed the file

With enforce: 'post' — Babel runs after OXC:

• ❌ __debugSourceDefine line numbers are wrong (Babel AST loc refers to OXC-transformed code, not the original source)
• ✅ OXC's jsxDEV() source info is correct (OXC saw the original source)

Reproduction

https://github.com/Artur-/vite-babel-order-repro

Steps to reproduce

npm install
npx vite

Open in browser — the page automatically verifies source positions.

System Info

System:
    OS: macOS 26.3.1
    CPU: (10) arm64 Apple M1 Max
  Binaries:
    Node: 24.14.0
    npm: 11.9.0

Used Package Manager

npm

Logs

No response

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