/** @noSelf */
declare namespace Test {
  export function testCallback<T extends (...args: any[]) => void>(
    callback: T,
  ): FunctionContainer<T>;
}

testCallback(() => {});

This fails with error TSTL: Unable to convert function with a 'this' parameter to function 'callback' with no 'this'. To fix, wrap in an arrow function, or declare with 'this: void'..

validateFunctionAssignment fails here. I could make it work by returning immediately if toType.isTypeParameter() is true, but I suspect that's not the correct solution to this particular problem.