💅 `lint/suspicious/noFallthroughSwitchClause` warns about a missing `break` even if TypeScript considers it unreachable due `never`.

[Lucas Garron]

Environment information

Biome 1.5.2. This reproduces in the playground, so I think the rest of the output doesn't narrow anything down.

Rule name

lint/suspicious/noFallthroughSwitchClause

Playground link

https://biomejs.dev/playground/?code=LwAvACAAVABoAGUAcwBlACAAdAB5AHAAZQBzACAAZQBtAHUAbABhAHQAZQA6ACAAYABpAG0AcABvAHIAdAAgAHsAIABhAHIAZwB2ACwAIABlAHgAaQB0ACAAfQAgAGYAcgBvAG0AIAAiAG4AbwBkAGUAOgBwAHIAbwBjAGUAcwBzACIAOwBgAAoAZABlAGMAbABhAHIAZQAgAGcAbABvAGIAYQBsACAAewAKACAAIABjAG8AbgBzAHQAIABhAHIAZwB2ADoAIABzAHQAcgBpAG4AZwBbAF0AOwAKACAAIABjAG8AbgBzAHQAIABlAHgAaQB0ADoAIAAoAGMAbwBkAGUAPwA6ACAAbgB1AG0AYgBlAHIAKQAgAD0APgAgAG4AZQB2AGUAcgA7AAoAfQAKAAoAYwBvAG4AcwB0ACAAZwByAGUAZQB0AGkAbgBnAEMAbwBkAGUAIAA9ACAAYQByAGcAdgBbADAAXQA7AAoAcwB3AGkAdABjAGgAIAAoAGcAcgBlAGUAdABpAG4AZwBDAG8AZABlACkAIAB7AAoAIAAgAGMAYQBzAGUAIAAiAGEAIgA6ACAAewAKACAAIAAgACAAYwBvAG4AcwBvAGwAZQAuAGwAbwBnACgAIgBoAGkAIgApADsACgAgACAAIAAgAGUAeABpAHQAKAAwACkAOwAKACAAIAB9AAoAIAAgAGMAYQBzAGUAIAAiAGIAIgA6ACAAewAKACAAIAAgACAAYwBvAG4AcwBvAGwAZQAuAGwAbwBnACgAIgBoAG8AdwBkAHkAIgApADsACgAgACAAIAAgAGUAeABpAHQAKAAxACkAOwAKACAAIAB9AAoAIAAgAGQAZQBmAGEAdQBsAHQAOgAgAHsACgAgACAAIAAgAHQAaAByAG8AdwAgAG4AZQB3ACAARQByAHIAbwByACgAIgBJAG4AdgBhAGwAaQBkACAAZwByAGUAZQB0AGkAbgBnACAAYwBvAGQAZQAuACIAKQA7AAoAIAAgAH0ACgB9AAoA

Code from the playground link:

// These types emulate: `import { argv, exit } from "node:process";`
declare global {
  const argv: string[];
  const exit: (code?: number) => never;
}

const greetingCode = argv[0];
switch (greetingCode) {
  case "a": {
    console.log("hi");
    exit(0);
  }
  case "b": {
    console.log("howdy");
    exit(1);
    break;
  }
  default: {
    throw new Error("Invalid greeting code.");
  }
}

Expected result

Since the type of exit from node:process is (code?: number) => never, TypeScript considers any code that follows it to be unreachable.

However, Biome shows an error in case clauses if I remove an unreachable break statement:

I'd love it if Biome could match TypeScript's assessment in this case.

Code of Conduct

• I agree to follow Biome's Code of Conduct

[Ze-Zheng Wu]

This is a duplicate of biomejs/website#49