Vite `base` option not working with RSC module loading in browser

[pawelblaszczyk5]

Related plugins

• plugin-react

• plugin-react-swc

• plugin-react-oxc

• plugin-rsc

Describe the bug

Hello 👋

It seems like the base option with Vite results in invalid chunk loading in browser environment:

For /src/client.tsx request goes to http://localhost:5173/examplesrc/client.tsx - while debugging I found this:

vite-plugin-react/packages/plugin-rsc/src/browser.ts

Line 13 in df6a38e

return __vite_rsc_raw_import__(import.meta.env.BASE_URL + id.slice(1))

It seems like there's a slice(1) call for some reason. If I locally patched it to remove the slice - it works correctly, but I'm not sure why it was there in the first place 😄

I hope my investigation is helpful, thanks a lot in advance!

Reproduction

https://github.com/pawelblaszczyk5/rsc-base-reproduction

Steps to reproduce

1. Start with RSC default starter
2. Add base option to vite.config.ts
3. Run dev server, observe the error of loading client chunk in browser

System Info

System:
    OS: macOS 15.5
    CPU: (8) arm64 Apple M1 Pro
    Memory: 130.72 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 24.4.0 - ~/.local/state/fnm_multishells/2224_1752770938234/bin/node
    npm: 11.4.2 - ~/.local/state/fnm_multishells/2224_1752770938234/bin/npm
    pnpm: 10.13.1 - ~/.local/state/fnm_multishells/2224_1752770938234/bin/pnpm
    bun: 1.1.33 - ~/.bun/bin/bun
  Browsers:
    Chrome: 138.0.7204.101
    Edge: 120.0.2210.121
    Safari: 18.5
  npmPackages:
    @vitejs/plugin-react: latest => 4.6.0 
    @vitejs/plugin-rsc: latest => 0.4.12 
    vite: ^7.0.4 => 7.0.5

Used Package Manager

pnpm

Logs

N/A here

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.

[hi-ogawa]

We have a test case and I thought base is expected to have trailing / (or at least Vite normalizes during resolve config) 🤔

vite-plugin-react/packages/plugin-rsc/examples/basic/vite.config.ts

Lines 20 to 21 in df6a38e

	export default defineConfig({
	base: process.env.TEST_BASE ? '/custom-base/' : undefined,

I think it would be simpler if we assume one format. Vite is probably currently too loose and it uses a little utilities like joinUrlSegments and stripBase in many places and personally I don't want to bring that one here yet.

[hi-ogawa]

OK, Vite indeed normalizes config.base but not for import.meta.env.BASE_URL. https://github.com/vitejs/vite/blob/27a192fc95036dbdb6e615a4201b858eb64aa075/packages/vite/src/node/config.ts#L1470

  const BASE_URL = resolvedBase
  ...
  const base = withTrailingSlash(resolvedBase)

I think we can try normalizing BASE_URL too on Vite and see what will happen.

[pawelblaszczyk5]

Oh I see - I completely didn't thought of adding '/' to the base path 😄

[hi-ogawa]

I tried changing Vite but probably it would be breaking change and have unknown consequence. For now, I'll address it here #589.