Remote functions generating empty sourcemaps

[DJMogens]

Describe the bug

The internal vite-plugin-sveltekit-remote Vite plugin's transform hook modifies .remote.* files but doesn't return a map property in either code path (SSR or client). This causes:

Vite build warnings: [plugin vite-plugin-sveltekit-remote] Sourcemap is likely to be incorrect — once per .remote.* file, for both SSR and client builds.
Broken sourcemaps: The resulting .js.map files have "sources": [], "sourcesContent": [], and semicolon-only "mappings". Error monitoring tools (e.g. Sentry) cannot map stack traces back to the original source.
SSR path (~line 727 in src/exports/vite/index.js): Appends init code via string concatenation and returns a bare code string — no map.

Client path (~line 803): Replaces the module entirely and returns { code: result } — no map.

Per the Vite plugin API, transform hooks should return { code, map }.

transform(src, id) {
  if (fileRegex.test(id)) {
    return {
      code: compileFileToJS(src),
      map: null, // provide source map if available
    }
  }
},

I intend to submit a PR for this.

Reproduction

Stackblitz reproduction:
https://stackblitz.com/~/github.com/DJMogens/sveltejs-kit-sourcemap-bug
To reproduce:

npm install
npm run build   # ← shows warnings + broken sourcemaps

Logs

@sveltejs/kit@2.53.4 ✔
vite v7.3.1 building ssr environment for production...
✓ 201 modules transformed.
[plugin vite-plugin-sveltekit-remote] Sourcemap is likely to be incorrect: a plugin (vite-plugin-sveltekit-remote) was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help
vite v7.3.1 building client environment for production...
✓ 168 modules transformed.
[plugin vite-plugin-sveltekit-remote] Sourcemap is likely to be incorrect: a plugin (vite-plugin-sveltekit-remote) was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help

System Info

(from stackblitz as the bug is also apparent here)
  System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 20.19.1 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.8.2 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    @sveltejs/adapter-auto: ^7.0.0 => 7.0.1 
    @sveltejs/kit: ^2.48.5 => 2.53.4 
    @sveltejs/vite-plugin-svelte: ^6.2.1 => 6.2.4 
    svelte: ^5.43.8 => 5.53.6 
    vite: ^7.2.2 => 7.3.1 


My local system where it was first noted:
   OS: Windows 11 10.0.26200
    CPU: (24) x64 13th Gen Intel(R) Core(TM) i7-13700K
    Memory: 34.02 GB / 63.76 GB
Binaries:
    Node: 22.17.1
    pnpm: 10.29.3
Browsers:
    Chrome: 145.0.7632.117
    Edge: Chromium (141.0.3537.71)
npmPackages:
    svelte: 5.49.1
    @sveltejs/kit: 2.53.4
    @sveltejs/adapter-node: 5.5.4
    @sveltejs/vite-plugin-svelte: 6.2.0
    vite: 7.1.3

Severity

annoyance

Additional Information

For us this was needed to upload the sourcemaps to sentry.

[teemingc]

I can't reproduce this with Vite 8 and vite-plugin-svelte 7. I guess Rolldown must be generating the sourcemaps for us. I think I'll close this in favour of that