Protect commands from using the wrong options

[kumar303]

We have command handlers like:

export function build({sourceDir}) {
  // work with sourceDir...
}

which rely on the main program from parsing --source-dir and passing it like build({sourceDir: ...}).

I would like to find a way to guarantee that command handlers are declaring only the available option arguments. One solution is to execute unnecessary code such as the main program code for every unit test of a function. I'd like to avoid that if possible since it could introduce slowness (maybe it's not so slow?).

I thought I could do this with Flow and did so in #39 but as of #105 it is becoming difficult to maintain so I removed it.

[kumar303]

Using strong typing (#1144) might solve this.