False positive for "Unreachable code detected" for code following `switch`/`case` with `allowUnreachableCode: false`

🔎 Search Terms

"false positive allowUnreachableCode"
"allowUnreachableCode case statement"
"Unreachable code detected case statement"

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about switch/case

⏯ Playground Link

https://www.typescriptlang.org/play/?#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-aDRGQWHEs2Vc+KOoX-qWc3nPQWyEA

💻 Code

type Foo = "bar" | "baz"

const fn = (value: Foo): number => {
    switch(value) {
        case "bar":
            return 1;
        case "baz":
            return 2;
    }

    return assertNever("nope!");
}

🙁 Actual behavior

return assertNever("nope!");

is highlighted as "Unreachable code detected". The docs, however, state:

This does not affect errors on the basis of code which appears to be unreachable due to type analysis.

🙂 Expected behavior

No error. This should be the same as the other case form, the if form, and various similar constructs where even though it's allegedly exhaustive, that's just based off of type information (I would like to have a runtime assertion in this case).

Additional information about the issue

Possibly related to: https://github.com/microsoft/TypeScript/issues/18882

Inizia con la riproduzione collegata in TypeScript Playground e confronta l’esempio di switch/case con le altre forme di case descritte nel report. Esamina il possibile issue correlato #18882, quindi verifica che l’asserzione a runtime dopo lo switch esaustivo non venga più segnalata come irraggiungibile, mentre il comportamento esistente per il codice irraggiungibile rimane invariato.