It looks like you've sent a pull request to update our 'lib' files. These files aren't meant to be edited by hand, as they consist of last-known good states of the compiler and are generated from 'src'. Unless this is necessary, consider closing the pull request and sending a separate PR to update 'src'.

All CLA requirements met.

It looks like you've sent a pull request to update our 'lib' files. These files aren't meant to be edited by hand, as they consist of last-known good states of the compiler and are generated from 'src'. Unless this is necessary, consider closing the pull request and sending a separate PR to update 'src'.

Your change don't work correctly (playground):

function assign<Source extends {}, Result extends Source>(
    target: Source,
    ...sources: Source[]
): Pick<Result, keyof Source> {
    return Object.assign(target, ...sources);
}

let y1 = assign(
    () => "",
    {
        version: 1
    }
);

let y2 = Object.assign(
    () => "",
    {
        version: 1
    }
);

y1 (using your change) has an error on version property:

Argument of type '{ version: number; }' is not assignable to parameter of type '() => string'.
  Object literal may only specify known properties, and 'version' does not exist in type '() => string'.

but y2 (using existing Object.assign definition) has no problems.

It'd be best to start with an issue describing non-working scenarios and outlining tests. We can't really evaluate a PR without first understanding why it's being made. I think the comment from @j-oliveras is instructive - this would likely be a large compat problem.