SwiftUI: how to size to fit a Button to expand to fill a VStack or HStack parent View?

Setting .infinity as the maxWidth, the frame(minWidth: maxWidth: minHeight:) API can be used to make a subview expand to fill:

VStack(alignment: .center, spacing: 20) {

    NavigationLink(destination: CustomView()) {
        Text("Button")
    }.frame(minWidth: 100, maxWidth: .infinity, minHeight: 44)
        .background(Color.primary)

    Button(action: { self.isShowingAlert = true }) {
        Text("Another Button")
    }.frame(minWidth: 100, maxWidth: .infinity, minHeight: 44)
        .background(Color.primary)

}.frame(width: 340)
    .background(Color.secondary)