Switch not narrowed when there is an extra pair of braces.

[JeanMeche]

🔎 Search Terms

• switch
• narrowing

🕗 Version & Regression Information

This is not a regression, it never worked.

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.2.2#code/JYOwLgpgTgZghgYwgAgEJwM4oN4ChnJgCeADhAFzIDkMA9rVcgD7UBGcUVuAvrrqJFiIUAMXrIIAD0ggAJhjSYc+QqQrU6DANwrNlDGCigA5jt79w0eEkVQJ0iHIXosyPAWJlKVdpx0FfShAAVwBbVmgzPhhgkAQwYFoQZGMIMAA1AAoASkoxWmZbNxUCKDTgqGSQgBtqgEIo3AQkg2QAN2QAXhS0rOydfhhMzLaAOk8IbK7O7p8OKin3dvG1Hj5cAHoN5AB1WigAawxcDAB3YDAEAAtkEZWyReQt5AAeGc6VBCU2efIS5d8-gIyFYZTgBwGBC+rho9Cof2By00QICYIha022wAIrQIAoQLQwMhTvsDidzpcbsMxhNso9nm8Zp9vnNOAjgWNAf9QRBwZDkNCULCGOyCGNkdy0WYgA

💻 Code

interface Base {
  type: 'foo' | 'bar'
}

interface Foo extends Base {
  type: 'foo';
  foo: string;
}

interface Bar extends Base {
  type: 'bar';
  bar: number;
}

function getV(): Foo | Bar {
    return null!;
}

const v = getV();

if((v.type) === 'bar') {
  v.type
}


// Works
switch (v.type) { // <===
  case 'bar':
    v.bar;
    break;

  case 'foo':
    v.foo;
    break;
}

// Does not work
switch ((v.type)) { // <===
  case 'bar':
    v.bar; // KO
    break;

  case 'foo':
    v.foo; // KO
    break;
}

🙁 Actual behavior

With extra braces in the switch, narrowing is broken.

switch ((v.type)) { // <=== extra braces
  case 'bar':
    console.log(v.bar);
    break;

  case 'foo':
    console.log(v.foo);
    break;
}

🙂 Expected behavior

switch ((v.type)) should behave as switch (v.type).

There is no such issue on a if condition.