Prerequisites

• I'm using the latest version
• I've read the relevant documentation
• I've searched for existing issues
• I've checked the list of known issues
• I've read the issue reproduction guide

Reproduction url

https://codesandbox.io/p/devbox/h4h4v7

Reproduction access

• I've made sure the reproduction is publicly accessible

Description of the issue

Vitest correctly recognizes relative paths to setupFiles from a root Vitest config file. However, if you use Vitest's Test Projects feature, relative paths from the project-level config files are not resolved correctly:

Root Vitest config (vitest.config.mts)

export default defineConfig({
  test: {
    projects: ["app/vitest.config.mts"],
  },
});

Project config (app/vitest.config.mts)

export default defineConfig({
  test: {
    setupFiles: ["./__test__/vitest.setup.ts"],
  },
});

Knip output

Unused files (1)
app/__test__/vitest.setup.ts  
Unresolved imports (1)
./__test__/vitest.setup.ts  app/vitest.config.mts