rollup-plugin: emitFile rejects relative paths in name field with rolldown 1.0.0-rc.12

[ericmatthys]

Description

The renderChunk hook in @vanilla-extract/rollup-plugin passes moduleInfo.id directly as the name field in this.emitFile():

https://github.com/vanilla-extract-css/vanilla-extract/blob/master/packages/rollup-plugin/src/plugin.ts#L155

const assetId = this.emitFile({
  type: 'asset',
  name: moduleInfo.id,  // can be a relative path like "../styles/src/focusRing.css.ts.vanilla.css"
  source: moduleInfo.meta.css
});

When a .css.ts file imports from another package (e.g. @vanilla-extract/rollup-plugin processing a component that imports tokens from a shared styles package), moduleInfo.id resolves to a relative path like ../styles/src/focusRing.css.ts.vanilla.css.

This worked with rollup/older rolldown versions, but rolldown 1.0.0-rc.12 (shipped with tsdown 0.21.x) now validates that name is neither an absolute nor relative path:

Error: The "fileName" or "name" properties of emitted chunks and assets must be strings
that are neither absolute nor relative paths, received "../styles/src/focusRing.css.ts.vanilla.css".

Suggested Fix

Use path.basename(moduleInfo.id) instead of moduleInfo.id for the name field:

const assetId = this.emitFile({
  type: 'asset',
  name: path.basename(moduleInfo.id),
  source: moduleInfo.meta.css
});

The name field is only used for generating the output filename (via assetFileNames), so stripping the directory prefix should be safe.

Reproduction

1. Create a package with a .css.ts file that imports from another package's .css.ts file
2. Build with tsdown >= 0.21.0 (which bundles rolldown 1.0.0-rc.12)
3. Build fails with the error above

Versions

• @vanilla-extract/rollup-plugin: 1.5.1 (also reproducible on 1.5.3)
• tsdown: 0.21.7
• rolldown: 1.0.0-rc.12