Function rust_type 

pub fn rust_type(
    ty: &ResolvedType,
    registry: &TypeRegistry,
    needs_box: &HashSet<(TypeId, usize)>,
    context: Option<(TypeId, usize)>,
) -> String

Convert a ResolvedType to its Rust type string. needs_box contains (type_id, field_index) pairs that need Box wrapping. current_context is Some((type_id, field_index)) when we’re in a boxed context.