Fixed type narrowing in switch statements with parenthesized expressions

[Mateusz Burzyński (Andarist)]

fixes #56030

[Joost Koehoorn (JoostK)]

Ah, you beat me to it :) I would have thought it was something like this. Thanks for providing the fix (and the incredible work you do for TypeScript, really)

[Mateusz Burzyński (Andarist)]

Thanks :)

[Jake Bailey (jakebailey)]

I merged this, but I should have run the tests. In light of #56020, is there a problem here in JS code which casts the argument to a switch, e.g.:

switch (/** @type { "a" | "b" } */ (foo)) {
	case "a":
		return;
	default: {
		const x: "b" = foo;
	}
}

[Jake Bailey (jakebailey)]

Ah, yes, you should be using:

skipParentheses(node, /*excludeJSDocTypeAssertions*/ true)

[Jake Bailey (jakebailey)]

Hm, I can't seem to make a test case where this fails. I thought this would show a difference but it does not:

// @strict: true
// @noEmit: true
// @checkJs: true
// @allowJs: true

// @filename: index.js

let value = "";

switch (/** @type {"foo" | "bar"} */ (value)) {
  case "bar":
    value;
    break;

  case "foo":
    value;
    break;

  case "invalid":
    value;
    break;
}

(namely, I would have expected value to not narrow...)

[miinabot]

Mateusz Burzyński (@Andarist) I saw this in my email and thought it was Emotion, congratulations on being a TypeScript contributor!!1!