feat(eslint-plugin): [switch-exhaustiveness-check] add requireDefaultForNonUnion option

[ST-DDT]

PR Checklist

• Addresses an existing open issue: fixes [switch-exhaustiveness-check] Require default case if discriminant type is not a union #2959
• That issue was marked as accepting prs
• Steps in Contributing were taken

Overview

This PR adds the requireDefaultForNonUnion option to the switch-exhaustiveness-check rule.
If enabled, all switches on non-union types require a default case to ensure they are "exhaustive".
The rule is disabled by default, although I would recommend changing this in a future major release, because why would you not want all of your switch cases to be exhaustive.

The rule already has the check for union types so it was easy to use the else branch to add the check for the default case.

const value: number = Math.floor(Math.random() * 3);

switch (value) {
  case 0:
    return 0;
  case 1:
    return 1;
}

->

const value: number = Math.floor(Math.random() * 3);

switch (value) {
  case 0:
    return 0;
  case 1:
    return 1;
  default: { throw new Error('default case') }
}

This cannot be achieved with the default-case rule, because that also requires the default case for union types which would hide the potential errors caused by extending the union with another case.

[typescript-eslint]

Thanks for the PR, @ST-DDT!

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!

---

🙏 Please, if you or your company is finding typescript-eslint valuable, help us sustain the project by sponsoring it transparently on https://opencollective.com/typescript-eslint.

[netlify]

✅ Deploy Preview for typescript-eslint ready!

Name	Link
🔨 Latest commit	9a8ae4c
🔍 Latest deploy log	https://app.netlify.com/sites/typescript-eslint/deploys/655a1fdfe30cfc0008def515
😎 Deploy Preview	https://deploy-preview-7880--typescript-eslint.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
Lighthouse	1 paths audited Performance: 90 (🔴 down 8 from production) Accessibility: 100 (no change from production) Best Practices: 92 (no change from production) SEO: 98 (no change from production) PWA: 80 (no change from production) View the detailed breakdown and full score reports

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[nx-cloud]

☁️ Nx Cloud Report

CI is running/has finished running commands for commit 7b77360. As they complete they will appear below. Click to see the status, the terminal output, and the build insights.

📂 See all runs for this CI Pipeline Execution

---

✅ Successfully ran 19 targets

• nx test eslint-plugin --coverage=false
• nx test visitor-keys --coverage=false
• nx run types:build
• nx test repo-tools --coverage=false
• nx run repo-tools:postinstall-script
• nx test utils --coverage=false
• nx test scope-manager --coverage=false
• nx test type-utils --coverage=false
• nx test eslint-plugin-tslint --coverage=false
• nx run-many --target=lint --parallel
• nx test typescript-estree --coverage=false
• nx test rule-schema-to-typescript-types --coverage=false
• nx test parser --coverage=false
• nx test eslint-plugin-internal --coverage=false
• nx test ast-spec --coverage=false
• nx run-many --target=typecheck --parallel
• nx run eslint-plugin:generate:configs
• nx run integration-tests:test
• nx run-many --target=build --parallel --exclude=website --exclude=website-eslint

---

Sent with 💌 from NxCloud.

[JoshuaKGoldberg]

LGTM, thanks! Just a little bit of nitpicking left - if you don't like the suggestions or don't have a chance to address them, no worries. We can merge roughly as-is.

[JoshuaKGoldberg]

✨ swell, thanks!

[JoshuaKGoldberg]

Ah, merge conflicts. I'll take care of them and merge.

[JoshuaKGoldberg]

Integration test failures are unrelated. 5dbf622

[ArnaudBarre]

Thank you very much for this! Love this <3

But more me this more close to the bug fix, this option should not exist and always be enabled. I don't think anyone choosing to enable this rule will be agaisnt having this check that really catch bugs or shows a missing union in your types

[ST-DDT]

@ArnaudBarre Should we create a new issue for that?

[JoshuaKGoldberg]

That would be the general right practice, yes 🙂. But I can tell you right now that this rule is far opinionated to not have this as an option. As a user of it I would maybe only ever use it for unions. It'd be quite restrictive to have it apply to all switch statements. Sometimes you really just want to switch over a few values! It's IMO not our place as a linter to tell people not to use a totally valid pattern of code like that.

I'm not saying this to shut your ideas down. If you feel strongly that I'm wrong here and we should discuss in an issue, then absolutely let's continue the conversation there. We can always discuss there, and even if it's not immediately accepted we can always put the evaluating community engagement label on it. Just posting now as a warning before you go through the effort of filing an issue. 😄

[ST-DDT]

@ArnaudBarre Should we create a new issue for that?

Done: #7966

• Enhancement: [switch-exhaustiveness-check] Turn on requireDefaultForNonUnion by default #7966