"Both esbuild and oxc options were set" on Vite 8.0.0-beta.16 + Vitest 4.1.0-beta.6

[wojtekmaj]

Describe the bug

When running unit tests, I'm seeing a warning:

Both esbuild and oxc options were set. oxc options will be used and esbuild options will be ignored. The following esbuild options were set: `{ legalComments: 'inline' }`

The thing is, neither in my vitest.config.ts nor vite.config.ts I have esbuild.legalComments option set. I only have build.rolldownOptions.output.legalComments set.

I believe this comes from the following default:

vitest/packages/browser/src/node/plugin.ts

Lines 358 to 361 in 0c2c013

	if (viteConfig.esbuild !== false) {
	viteConfig.esbuild ||= {}
	viteConfig.esbuild.legalComments = 'inline'
	}

but following intuition and setting esbuild: false in my Vitest config, I just get a different warning:

`esbuild` option is set to false, but `oxc` option was not set to false. `esbuild: false` does not have effect any more. If you want to disable the default transformation, which is now handled by Oxc, please set `oxc: false` instead.

Reproduction

I believe I have provided sufficient information for this bug to be resolved. If I'm mistaken, please let me know!

System Info

System:
    OS: macOS 26.3
    CPU: (10) arm64 Apple M1 Max
    Memory: 834.45 MB / 64.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 24.11.1 - /usr/local/bin/node
    Yarn: 4.10.3 - /Users/wojciech.maj/.yarn/switch/bin/yarn
    npm: 11.6.2 - /usr/local/bin/npm
  Browsers:
    Chrome: 144.0.7559.134
    Firefox: 141.0.3
    Safari: 26.3

Used Package Manager

npm

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

[hi-ogawa]

@wojtekmaj you likely have plugin which is setting oxc option, so reproduction would help.

[wojtekmaj]

That's the latest beta of @vitejs/plugin-react, 6.0.0-beta.0. I expect a lot of people will hit that problem soon.