Declaration merging: remove function overloads?

Let’s say one of the libs come with a function like this:

// library:
declare module 'example' {
    interface Animal { }
    export function sayHello(a: Animal);
}

I want to narrow down the type to just Dog. This is my module augmentation:

// app.ts
declare module 'example' {
    interface Dog extends Animal { }
    export function sayHello(a: Dog);
}

This merges the declarations to two function overloads:

sayHello(a: Dog);
sayHello(a: Animal);

I’d like to remove the generic Animal one to get stricter type checking of my code.

I couldn’t find if this has been discussed before but I would find it useful quite often. Some examples would be:

• express headers (string by default, I’d use union of string literals)
• yargs args (I’d limit them to args specific to my app)

[jcalz]

Could someone articulate how negated/subtraction types would allow declaration merging to remove existing overloads? I don’t see the connection (and therefore I don’t see why this is a duplicate of #4183)

[jcalz]

Sounds like you need to copy the library’s declaration files, modify the declarations you care about, and include/import only the locally-modified declaration files in your code.