Describe the bug

Using coverage.autoUpdate in a configuration to update the thresholds will strip intended whitespace/newlines from the bottom of configuration files.

This goes against common linting rules like eslint/prettier-prettier that enforce newlines at the end of files, meaning that on-update the build will generally fail CI builds, if linting is enabled there.

The workaround is to ignore the role in the second-to-last line:

import { configDefaults, defineConfig } from 'vitest/config';

export default defineConfig({
  test: {
    globals: true,

    coverage: {
      enabled: true,
      provider: 'istanbul',
      thresholds: {
        autoUpdate: (newThreshold: number): number =>
          newThreshold >= Math.floor(newThreshold) + 0.2 ? Math.floor(newThreshold) : Math.floor(newThreshold) - 1,
        statements: 56,
        branches: 47,
        functions: 58,
        lines: 56,
      },
      reporter: ['json', 'json-summary', 'text', 'cobertura', 'html'],
      include: ['lib/**/*.ts'],
    },

    exclude: [...configDefaults.exclude, '**/dist/**/*'],
  },
  // eslint-disable-next-line prettier/prettier
});

but it'd be nice if only the thresholds part of the file was replaced, preferably just the numbers. In general it's hard to conform to all linters, since something like 56.<many digits>1 may want to wrap to a new line:

lines:
  56.0000000000000000000000000000000000001

so maybe the real solution is to offer a post-update script that could be run to format. Appending to our "test" script to format is ugly and also doesn't work in Monorepos that lint/format from the top-level, not individually in each package.

Reproduction

Configure eslint with the prettier plugin.

Run tests, the coverage doesn't even have to change.

See that the newline is stripped off of vitest.config.ts.

System Info

System:
    OS: Linux 5.10 Amazon Linux 2
    CPU: (32) arm64 unknown
    Memory: 101.18 GB / 123.55 GB
    Container: Yes
    Shell: 5.8.1 - /bin/zsh
  Binaries:
    Node: 20.18.0 - ~/.local/share/mise/installs/node/20/bin/node
    npm: 10.8.2 - ~/.local/share/mise/installs/node/20/bin/npm
  npmPackages:
    vitest: ^3 => 3.2.4

Used Package Manager

npm

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