Checking if Enum | falsely in if condition if value of Enum might be zero

Suggestion

🔍 Search Terms

checker, enum, undefined, dx

✅ Viability Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion

Check if a value has enum | falsely types, and one member of the enum is zero. And the value In top level of If/while/etc's conditions.

It's a common bug case. Even after condition, CFA could strip the zero value. But If we does not use the enum value, we will never find it out.

📃 Motivating Example

enum E {
    Foo,
    Bar
}

function foo (v: E | undefined) {
    if (!v) { // Should be suggestion or error?
        throw new Error("Hoops")
    }

    console.log("Acceptable") // But without E.foo
}

💻 Use Cases

Commencez par l’exemple motivant E | undefined et examinez le comportement du checker pour le narrowing par vérité dans les conditions if. Déterminez si le résultat doit être une suggestion ou une erreur, puis définissez des tests couvrant un membre d’enum de valeur zéro et le type narrowed ; le travail est terminé lorsque le comportement de diagnostic attendu est spécifié et couvert.