Odd behavior with GeometryReader and Path

Question

Could someone explain to me why a simple - 1 for container width fixes alignment problems with Color and Path in HStack.

Without -1 I get this, where the Path dissapears from the view:

But with the -1 it works as intended:

Full code:

struct SlantedBackground: View {
    let color: Color

    var body: some View {
        GeometryReader { geometry in
            HStack(spacing: 0) {
                color
                    // This is where the problem is.
                    // This works
                    .frame(width: geometry.size.width - 1, height: geometry.size.height)
                    // This does not
                    .frame(width: geometry.size.width, height: geometry.size.height)
                Path { path in
                    path.move(to: CGPoint(x: 0, y: 0))
                    path.addLine(to: CGPoint(x: 0, y: geometry.size.height))
                    path.addLine(to: CGPoint(x: 16, y: 0))
                    path.closeSubpath()
                }.fill(color)
            }
        }
    }
}