The C++ code generator now handles schemas where the top-level type is
nullable ("type": ["object", "null"], ["string", "null"], or
["array", "null"]).
Changes to weaseljson_schemagen.py:
- Rename the inner object struct when the root is a nullable object, so
the `using Root = std::optional<...>` alias no longer conflicts with
`struct Root`.
- Treat nullable root objects and arrays as container roots, emplacing
the inner value before pushing the root frame and pointing the frame at
the contained value.
- For nullable root scalars/enums, engage() now returns a pointer to the
value inside the optional rather than to the optional wrapper itself.
- cbNull() now safely accepts a top-level null when the root is nullable
and rejects it otherwise.
Regression tests added:
- nullable_object.schema.json + test_nullable_root.cpp
- nullable_string.schema.json
- nullable_array.schema.json
Closes#13
weaselbot