Having the data's schema be optional at the level of the 'Schema' did not allow to represent cases where there would be an opaque data at an arbitrary nesting. So I introduced a new variant 'Opaque' on 'Data' to fill that gap.
Here's a trick though: I got lazy (a bit) and did not write a full deserializer for Schema because this is busywork and not at all necessary at this stage. Instead, I've made the blueprint parameterized by a generic type <T>; which represents the type of the underlying blueprint's schema. When deserializing from JSON, we can default to 'Value' to get a free deserializer. Since all we're interested about is the program and the metadata (purpose and title) of a validator, it works nicely.
Serialization however expects a Blueprint<Schema>, and most of the functions operates over a Blueprint<Schema> anyway.
This also now introduce two levels of representable types (because it's needed at least for tuples):
Plutus Data (a.k.a Data) and UPLC primitives / constants (a.k.a Schema).
In practice, we don't want to specify blueprints that use direct UPLC primitives because there's little support for producing those in the ecosystem. So we should aim for producing only Data whenever we can. Yet we don't want to forbid it either in case people know what they're doing. Which means that we need to capture that difference well in the type modelling (in Rust and in the CIP-0057 specification).
I've also simplified the error type for now, just to provide some degree of feedback while working on this. I'll refine it later with proper errors.
The blueprint is generated at the root of the repository and is
intended to be versioned with the rest. It acts as a business card
that contains many practical information. There's a variety of tools
we can then build on top of open-source contracts. And, quite
importantly, the blueprint is language-agnostic; it isn't specific to
Aiken. So it is really meant as an interop format within the
ecosystem.
KtorZ