@switch type narrowing doesn't work

[ArielGueta]

Which @angular/* package(s) are the source of the bug?

compiler

Is this a regression?

No

Description

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

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

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

@Component({
  selector: 'app-root',
  standalone: true,
  template: `
@switch (v.type) {
  @case ('bar') {
    {{ v.bar }}
  }

  @case ('foo') {
    {{ v.foo }}
  }

  @default {
    Default
  }
}
  `
})
export class AppComponent {
   v: Foo | Bar = { type: 'foo', foo: 'foo' };
}

Please provide a link to a minimal reproduction of the bug

No response

Please provide the exception or error you saw

No response

Please provide the environment you discovered this bug in (run ng version)

No response

Anything else?

It should work similar to typescript code.

[JoostK]

The reason this doesn't work is because the TCB contains a parenthesized expression as switch-condition, which is not accounted for in TS's CFA.

function _tcb1(this: AppComponent) { if (true) {
    switch (((((this).v /*10,11*/) /*10,11*/).type /*12,16*/) /*10,16*/) {
        case "bar" /*29,34*/:
            "" + (((((this).v /*45,46*/) /*45,46*/).bar /*47,50*/) /*45,50*/);
            break;
        case "foo" /*68,73*/:
            "" + (((((this).v /*84,85*/) /*84,85*/).foo /*86,89*/) /*84,89*/);
            break;
        default: break;
    }
} }

[ArielGueta]

It should be fixed, right?

[crisbeto]

It might be worth changing switch to use if statements in the TCB as well.

[crisbeto]

Confirmed Joost's explanation here: https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgEJwM4oN4ChnJgCeADhAFzIDkMA9rVcgD7UBGcUVuAvrrqJFiIUAMXrIIAD0ggAJhjSYc+QqQrU6DANwrNlDGCigA5jt79w0eEkVQJ0iHIXosyPAWJlKVdpx0FfShAAVwBbVmgzPhhgkAQwYFoQZGMIMAA1AAoASkoxWmZbNxUCKDTgqGSQgBtqgEIo3AQkg2QAN2QAXhS0rOydXAB6QeQAdVooAGsMXAwAd2AwBAALZEy2gDpPCGziggQlNg4qchLkZpAMWmqIDeraY3WN336z1jK4SYH9w5p6E7OFyuNzuDyemleBACHy+PD4w2QABFaBAFCBaGBkHMJpNZgslqtMk9ttldu5zr9fACoecWtdbvdHpsXv4oe8IJ9vhTXH8GKcaUD6aCmRsIazoRzYdwgA

[JeanMeche]

FWIW the root issue is fixed on TS' side microsoft/TypeScript#56035