There are range-finder cameras that present you with two windows to look through.
The larger, brighter one you use for framing your subject.
The smaller, "squintier" one is used just for focussing - it has a coupled range-finder patch that you align for focussing. The view through that window may only be part of the scene.
I don't know if there are Leica versions of this approach, but there certainly are others. The rangefinder versions of the Kodak 35 are an example.