Describe the bug

In vitest 4.0.16 browser mode (@vitest/browser + Playwright runner), when a raw Symbol value is passed directly as a console.log / console.error argument, the baseFormat function in @vitest/utils throws a TypeError.

The root cause is that baseFormat uses str += \${x}`for non-object trailing arguments. JavaScript does not allow implicit string conversion of Symbols via template literals, so this throwsTypeError: Cannot convert a Symbol value to a string`.

// DOES crash in vitest 4.0.16
console.log('value:', Symbol('test'))
// → TypeError: Cannot convert a Symbol value to a string

// Does NOT crash (Symbol as object key is handled differently)
console.error('Test error:', { status: 400, [Symbol('rtk-query')]: { type: 'error' } })

This is a regression from 4.0.15.

Reproduction

https://github.com/Suto-Michimasa/vitest-symbol-repro

Steps to reproduce

git clone https://github.com/Suto-Michimasa/vitest-symbol-repro
cd vitest-symbol-repro
pnpm install
pnpm test:browser

Stack trace

TypeError: Cannot convert a Symbol value to a string
    at baseFormat (@vitest/utils@4.0.16/dist/display.js:700:15)
    at browserFormat (@vitest/utils@4.0.16/dist/display.js:711:9)
    at processLog (__vitest_browser__/tester.js:1202:10)
    at console.error (__vitest_browser__/tester.js:1198:23)

Root cause

In @vitest/utils baseFormat function:

// display.js:700 (simplified)
str += `${x}`  // Throws TypeError when x is a Symbol

The fix should use String(x) instead of template literal interpolation, as String(Symbol('test')) safely returns "Symbol(test)".

Regression confirmation

Downgrading to 4.0.15 resolves the issue:

pnpm up vitest@4.0.15 @vitest/browser@4.0.15 @vitest/browser-playwright@4.0.15
pnpm test:browser  # passes

Expected behavior

• Raw Symbol values should be safely handled during console output formatting (e.g., converted via String(symbol))
• Tests should pass without TypeError

Actual behavior

• Tests fail with TypeError: Cannot convert a Symbol value to a string
• The browser runner crashes when formatting raw Symbol values in console arguments

System Info

• vitest: 4.0.16
• @vitest/browser: 4.0.16
• @vitest/browser-playwright: 4.0.16
• playwright: 1.57.0
• Browser: Chromium (via Playwright)
• Node.js: 20+
• OS: macOS

Used Package Manager

pnpm

Validations

• Check that there isn't already an issue that reports the same bug
• The provided reproduction is a minimal reproducible example