plugin-rsc: inject-async-local-storage transform drops source maps

Related plugins

• plugin-react

• plugin-react-swc

• plugin-rsc

Describe the bug

The rsc:inject-async-local-storage transform changes modules containing both typeof AsyncLocalStorage and new AsyncLocalStorage(), but it does not return a source map for that transformation.

With Vite 8.2.1, the RSC and SSR builds emit SOURCEMAP_BROKEN naming this transform. The final emitted map cannot resolve a marker in the transformed source to any original position: the expected location is src/entry.js:6, while originalPositionFor returns source=null, line=null, column=null.

Expected: the transform preserves and composes source mappings, the marker resolves to src/entry.js:6, and Vite emits no source-map warning for this transform.

Actual: the transformed module loses its original mapping. This can cause incorrect or missing stack-frame symbolication in production error monitoring.

The likely location is globalAsyncLocalStoragePlugin, which prepends initialization text and returns only transformed code. I can submit a patch and test if maintainers confirm the preferred test location.

Reproduction

https://github.com/FieldArchiveTX/vite-plugin-rsc-sourcemap-repro

Steps to reproduce

1. Clone the reproduction repository.
2. Run npm ci.
3. Run npm run repro.
4. Observe two SOURCEMAP_BROKEN warnings for rsc:inject-async-local-storage and the verifier output showing a null original position.

The reproduction command exits successfully when the defect is reproduced.

System Info

System:
  OS: Windows 11 10.0.26200
  CPU: x64 Intel Core i7-14700KF
Binaries:
  Node: 24.14.0
  npm: 10.9.2
Browsers:
  Chrome: 150.0.7871.187
npmPackages:
  @vitejs/plugin-rsc: 0.5.34
  vite: 8.2.1
  react: 19.2.8
  react-dom: 19.2.8
  react-server-dom-webpack: 19.2.8

Used Package Manager

npm

Logs

[plugin rsc:inject-async-local-storage] [SOURCEMAP_BROKEN]
Sourcemap is likely to be incorrect: a plugin (rsc:inject-async-local-storage) was used to transform files, but didn't generate a sourcemap for the transformation.

expected: src/entry.js:6
traced: source=null, line=null, column=null

REPRODUCED: the emitted source map does not resolve the marker to its source line.

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

Start at the globalAsyncLocalStoragePlugin in the plugin-rsc package and run the linked reproduction with npm ci and npm run repro. Trace the rsc:inject-async-local-storage transform and identify the appropriate test location. Done means the transformed module preserves source mappings, the marker resolves to src/entry.js:6, and the SOURCEMAP_BROKEN warning is gone.