tsc produces invalid typings for parameter destructuring

[uber5001]

I have an interface that is supposed to have a function signature of:

(param: {prop: boolean}): any

but I forget the parameter name (I'm not sure if this signature is considered valid):

({prop: boolean}): any

When compiling this invalid interface with the --declaration flag, an invalid .d.ts file results:

/* foo.ts */
export interface SomeInterface {
    ({prop: boolean}): any
}

tsc foo.ts --module commonjs --declaration

/* foo.d.ts */
export interface SomeInterface {
    ({prop: }: {
        prop: any;
    }): any;
}

If parameter names are optional, this should produce a valid .d.ts file. If parameter names are required, tsc should throw an error, or at least warn me that there is an issue.

[RyanCavanaugh]

Parameter names are required in some form or another. {prop: boolean} is a destructuring parameter (a new ES6 feature) that takes the first argument and assigns its prop property into the boolean variable.

See #2023 for the bug about destructured parameters creating invalid .d.ts files

[uber5001]

Hey Ryan. I don't think this is a duplicate of #2023, as I'm not attempting to destructure anything here. Since parameter names are required (thank you for clarifying!), the issue is now that tsc does not throw any errors, and silently produces invalid output.

This was tested using the latest version of tsc, taken from master/bin/tsc. Some sort of error should be produced at compile-time instead of generating invalid output, right?

[RyanCavanaugh]

You're right. Thanks for following up -- I misread the linked bug.

[ahejlsberg]

Sadly, this is not a bug. The ES6 destructuring syntax is eerily similar to the syntax for object types. The following is perfectly valid ES6:

function foo({ prop: boolean }) {
    let x = boolean;  // Destructuring declares local named boolean of type any
}

foo({ prop: 42 });

Not entirely clear how we'd make something like that an error.

[mhegazy]

Just to clarify, the issue here is that the declaration file generated is not valid. there is an extra ":" emitted after "prop" in:

interface SomeInterface {
    ({prop: }: {
        prop: any;
    }): any;
}