@switch type narrowing doesn't work

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.

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;
    }
} }

It should be fixed, right?

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

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

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

I think we'll still have to keep the workaround around until we drop support for TS 5.2.

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fix(compiler): work around TypeScript bug when narrowing switch state…

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@switch type narrowing doesn't work #52077

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

Is this a regression?

Description

Please provide a link to a minimal reproduction of the bug

Please provide the exception or error you saw

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

Anything else?

Metadata

Assignees

Labels

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Projects

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@switch type narrowing doesn't work #52077

Description

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

Is this a regression?

Description

Please provide a link to a minimal reproduction of the bug

Please provide the exception or error you saw

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

Anything else?

Activity

JoostK commented on Oct 6, 2023

ArielGueta commented on Oct 7, 2023

crisbeto commented on Oct 7, 2023

crisbeto commented on Oct 8, 2023

JeanMeche commented on Oct 9, 2023

crisbeto commented on Oct 9, 2023

angular-automatic-lock-bot commented on Nov 9, 2023

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions

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