Generate more sensible constants

[vmchale]

This fixes #438

Before, we generated bad data for constants sometimes. This filters out that bad data (viz., integers which are out of range), which means that we no longer have to allow errors in the parser roundtrip tests.

[effectfully]

Filtering out generated stuff is generally a bad idea, because it often increases time required to generate correct test data. It's usually better to generate something correct by construction than to deal with estimating whether test time grows too much or not. Since in this case it's easy to generate correct by construction data, I think we should do that.

You can just generate Integers and ByteStrings, compute the minimal sizes they fit into and construct the corresponding Constants. We have functions that do the latter two actions in Language.PlutusCore.Constant.Make:

makeAutoSizedBuiltinInt :: Integer -> Constant ()
makeAutoSizedBuiltinBS :: BSL.ByteString -> Constant ()

So you only need to generate Integers and ByteStrings and then use the available functions.

[vmchale]

Fair enough.

[effectfully]

Oh, weird, we check that integers are in bounds during parsing, but do not perform the same check for bytestrings?

[vmchale]

Yes, that is correct. Perhaps put it in slack and we can discuss it at the next meeting if need be?

[michaelpj]

I'm pretty unconvinced that parsing is the right time for validity checks, but let's save that discussion for another time.