cssCodeSplit with multiple entry points emits bogus sourcemap files

[silverwind]

Describe the bug

When cssCodeSplit is enabled and multiple entry points with the same name but different file extension are present, vite generates invalid sourcemap files which refer nonexistant files and serve no purpose.

Reproduction

https://github.com/silverwind/vite-empty-sourcemap

export default defineConfig({
  build: {
    cssCodeSplit: true,
    sourcemap: true,
    lib: {
      entry: [
        "./index.js",
        "./index.css",
      ],
      formats: ["es"],
    },
  },
});

Steps to reproduce

git clone https://github.com/silverwind/vite-empty-sourcemap
cd vite-empty-sourcemap
npm install
npx vite build
ls -la dist

Expected

index.css
index.js
index.js.map

Actual

index.css
index.js
index.js.map
index2.js.map  <-- Bogus sourcemap file

The sourcemap refers to a nonexistant file index2.js:

cat dist/index2.js.map
{"version":3,"file":"index2.js","sources":[],"sourcesContent":[],"names":[],"mappings":";"}

System Info

System:
    OS: macOS 13.5
    CPU: (8) x64 Intel(R) Core(TM) i7-1060NG7 CPU @ 1.20GHz
    Memory: 141.58 MB / 16.00 GB
    Shell: 5.9 - /usr/local/bin/zsh
  Binaries:
    Node: 20.5.0 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 9.8.1 - ~/.npm-global/bin/npm
    pnpm: 8.6.11 - /usr/local/bin/pnpm
  Browsers:
    Chrome: 114.0.5735.133
    Safari: 16.6
  npmPackages:
    vite: 4.4.9 => 4.4.9

Used Package Manager

npm

Logs

Click to expand!

vite v4.4.9 building for production...
✓ 2 modules transformed.
dist/index.css  0.01 kB │ gzip: 0.03 kB
dist/index.js   0.09 kB │ gzip: 0.11 kB │ map: 0.16 kB
✓ built in 88ms

Validations

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• The provided reproduction is a minimal reproducible example of the bug.

[kinfuy]

It seems that it was caused by adding CSS files to the entry. I'm not sure if this is the expected behavior

[silverwind]

Yes, the CSS in entry this is intentional. I'm adding it there because I require the library consumer to explicity @import it in their CSS. I don't want to import CSS inside JS because that makes node unable to import the file (vitest-dev/vitest#3862 is related). FYI, this is how it looks in my package.json:

  "exports": {
    "./dist/*.css": {
      "import": "./dist/*.css"
    }
  }