Despite it's given an InlineConfig object, a secondary build script (with Vite build API JS ) still uses vite.config.js

[bogacg]

Describe the bug

On top of a primary build using vite.config.js (for multiple pages app) I execute a secondary build script (a build.mjs file) to get several JS files from another source directory into same output dist folder.

With Vite v3.1.2 (and prior) I do not have an issue and output js files are written to dist next to files coming from a previous step as expected.

However after I updated to v3.1.3 today, erroneous output files are written on top of previous ones.

As if Js files of secondary source folder are matched to each input of rollupOptions in defineConfig argument of vite.config.js.

I've prepared an example project with two NPM scripts.
You can see the problem running

• npm run build: only runs on src folder and then
• npm run two-builds that executes a custom build script on a secondary source folder after previous default.

Reproduction

https://github.com/bogacg/vite-3-1-3-js-build-api-bug

System Info

System:
    OS: Windows 10 10.0.19043
    CPU: (12) x64 AMD Ryzen 5 3600 6-Core Processor
    Memory: 8.47 GB / 15.92 GB
  Binaries:
    Node: 18.8.0 - C:\Program Files\nodejs\node.EXE
    npm: 8.18.0 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Edge: Spartan (44.19041.1266.0), Chromium (105.0.1343.42)
    Internet Explorer: 11.0.19041.1566

Used Package Manager

npm

Logs

No response

Validations

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

[sapphi-red]

This behavior was using a bug (#9086).

To stop reading config file automatically for build(), you'll need to set configFile: false.
https://vitejs.dev/guide/api-javascript.html#inlineconfig

  await build({
    build: {
      outDir: "./dist",
      lib: {
        ...lib,
        formats: ["es"],
      },
      emptyOutDir: false
    },
    configFile: false
  });