When declaring a function that takes variadic arguments followed by a required parameter, such as
this is accepted, but there's no way to call the function. Any attempt to do so fails with an error, e.g.
fails with the error
error: missing argument for parameter #2 in call
I consider this a bug, because this call is unambiguous. There is a single required parameter after the variadic arguments, which means that the last parameter in the call must correspond with this unnamed parameter.
More generally, Swift should be able to figure out how to invoke functions that have one or more unnamed parameters after the variadic parameter list as long as the unnamed parameters do not have default values.