Support inline expressions in validators

[nettad]

validator[_] { s =>
  val foo = s.bar //assume bar is some list

   foo has size > 10
}

Obviously this is a simple irrelevant example but it doesn't compile.

[holograph]

The transformation macro currently assumes that every expression in the validation block is a validation rule (i.e. typechecks to Validator[_]), and needs to be rewritten to be able to reorder such a block to a (list of statements; list of validators) tuple. Seems like a worthwhile endeavor, adding to 0.3 milestone roadmap.

[holograph]

I've written a proof-of-concept implementation on a separate branch, you can see the relevant tests here (the bottom Interleaving object).

It's currently severely limited in that it assumes ordering and doesn't do escape analysis; in simple terms, each validator "tacks on" the preceding code lines. This means something like val something = ...; something is notNull; something is notEmpty will not work because the second rule won't "get" the free code ranges.

I need to do some further research into the macro context/compiler architecture to see if it's feasible to do some sort of escape analysis to figure out which snippets of code are necessary for each validator; it's possible that the Async extensions for Scala have already solved this.

[nettad]

Nice!

[holograph]

The necessary mechanism for rewriting the code ended up being quite complex (equal to, or possibly rivalling, the complexity of the async/await code transformation). I wonder if there's enough interest in this feature to warrant the time?