Need a way to access flux options from builtins

[rockstar]

While trying to implement influxdata/influxdb/tasks/lastSuccess, I discovered that there's not a way to get an option defined in flux from inside a builtin. @wolffcm and I talked about it, and decided that it might be best to be able to get to the flux options from the context.Context from a function.

[jsternberg]

I'd need to know the specifics, but the best way to use an option inside of a builtin is likely to use some indirection. A few things to consider when using another value inside of a builtin. A builtin doesn't really understand the concept of closures which means that it doesn't really understand the concept of scope. But it does understand the concept of passing values. I've used this technique before:

option opt = 0
builtin _func
func = (v) => _func(v: v, opt: opt)

The builtin includes a parameter for the option and the user facing function will include it automatically. This causes the interpreter to take care of everything.