fix(eslint-plugin): [switch-exhaustiveness-check] fix new allowDefaultCaseForExhaustiveSwitch option

[Zamiell]

PR Checklist

• Addresses an existing open issue: fixes Bug: [switch-exhaustiveness-check] fails with option "allowDefaultCaseForExhaustiveSwitch": false #8165
• That issue was marked as accepting prs
• Steps in Contributing were taken

Overview

At first I thought this was a trivial fix to just check for isUnion, but then someone pointed out that it would fail for string | number, which is a union, but should actually have a default case.

Thus, I revert to creating a doesTypeContainNonLiteralType function.

[typescript-eslint]

Thanks for the PR, @Zamiell!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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[ArnaudBarre]

I was just hit by the issue when enabling this new option that looks good!
Thanks for already fixing it, but I'm a bit afraid the isUnion check can lead to issues, for example does default will be allow with: number | string switch or with "A" | "B" | string? Ideally what you want is to be able to detect if the switch type is finite or not

[Zamiell]

@ArnaudBarre You are right, I will add the following "allow" test to address this:

    // switch with default clause on primitive +
    // "allowDefaultCaseForExhaustiveSwitch" option
    {
      code: `
declare const value: number | string;
switch (value) {
  case 0:
    return 0;
  case 1:
    return 1;
  default:
    return -1;
}
      `,
      options: [
        {
          allowDefaultCaseForExhaustiveSwitch: false,
          requireDefaultForNonUnion: false,
        },
      ],
    },

[Zamiell]

In order to address this, I added a new prop to the metadata called containsNonLiteralType.

[JoshuaKGoldberg]

Thanks!