Bug: [switch-exhaustiveness-check] fails with option "allowDefaultCaseForExhaustiveSwitch": false

[danielrentz]

Before You File a Bug Report Please Confirm You Have Done The Following...

• I have tried restarting my IDE and the issue persists.
• I have updated to the latest version of the packages.
• I have searched for related issues and found none that matched my issue.
• I have read the FAQ and my problem is not listed.

Playground Link

https://typescript-eslint.io/play/#ts=5.3.3&fileType=.tsx&code=GYVwdgxgLglg9mABFApgZygCjALkWEAWwCMUAnASkQG8BYAKEUTQHcYoIALRbKuxpoggBDNCkQBGPGRRQQZJACYA3A0FDR4xdNnykAFlUCmAExTBhIADZQdchYgBsRpgF8G7%2BkA&eslintrc=N4KABGBEBOCuA2BTAzpAXGUEKQAIBcBPABxQGNoBLY-AWhXkoDt8B6ZAd0vzIAt6AHrwCGsZPkoA3RExTJafRGQDW6MAG1IiaNAD20SABpMUYfHi6OAEUQAzUfHwBhYckQAxfQFEho8VMQAZS4eXjV7eDcwAF8AXXAYkGigA&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eAcgK6qoDCAFutAGsylBm3TgwAXxCSgA&tokens=false

Repro Code

function test(n: number) {
  switch (n) {
    case 1: return 2;
    case 2: return 4;
    default: return 6;
  }
}

ESLint Config

module.exports = {
  parser: "@typescript-eslint/parser",
  "rules": {
    "@typescript-eslint/switch-exhaustiveness-check": ["error", { "allowDefaultCaseForExhaustiveSwitch": false }]
  }
};

tsconfig

{
  "compilerOptions": {
    // ...
  }
}

Expected Result

No error.

Actual Result

The switch statement is exhaustive, so the default case is unnecessary. 5:5 - 5:23

Additional Info

No response

[ehoogeveen-medweb]

In fact, with "requireDefaultForNonUnion": true also set it is not possible to write a compliant switch:

• with default gives "The switch statement is exhaustive, so the default case is unnecessary. 5:5 - 5:23"
• no default gives "Switch is not exhaustive. Cases not matched: default 2:11 - 2:12"

I wonder if the problem is that the switch statement is exhaustive only because of the default - so its presence makes it redundant, and its absence makes it necessary.

[Josh-Cena]

An infinite type definitely needs a default. I'm surprised this isn't covered by a test—cc @Zamiell

[Zamiell]

That looks like a bug, I'll investigate.

[Zamiell]

should be fixed in this PR, sorry about that

[danielrentz]

Thank you for the quick fix!