This is pretty narrow, and I don't love that the control flow is both implicit and hard-coded. I like @tera's suggestion to just add a very narrow "guard rebind":
{ [weak self, weak target] in
guard self?, target? else { return } // sugar for "guard let self = self, let target = target"
target.action(on: self) // self and target are non-optional here, and we would allow implicit use of non-optional self
}