1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145

//! # pocket_prover-derive
//!
//! Derive procedural macros for `pocket_prover`.
//!
//! Example:
//!
//! ```ignore
//! #[macro_use]
//! extern crate pocket_prover_derive;
//! extern crate pocket_prover;
//!
//! use pocket_prover::Construct;
//!
//! #[derive(Construct)]
//! pub struct Foo {
//!     pub a: u64,
//!     pub b: u64,
//! }
//! ```
//!
//! Since `pocket_prover` uses only `u64`,
//! it is the only valid concrete field type.
//!
//! The macro supports generic arguments, assuming that
//! the inner type implements `Construct`:
//!
//! ```ignore
//! #[derive(Construct)]
//! pub struct Bar<T = ()> {
//!     pub foo: T,
//!     pub a: u64,
//!     pub b: u64,
//! }
//! ```

extern crate proc_macro;
extern crate syn;
#[macro_use]
extern crate quote;

use proc_macro::{TokenStream};
use syn::{
    Body, Ident, VariantData, PolyTraitRef, Ty, TyParamBound,
    TraitBoundModifier, WherePredicate, WhereBoundPredicate
};
use quote::Tokens;

#[proc_macro_derive(Construct)]
pub fn construct(input: TokenStream) -> TokenStream {
    // Construct a string representation of the type definition
    let s = input.to_string();

    // Parse the string representation
    let ast = syn::parse_derive_input(&s).unwrap();

    // Build the impl
    let gen = impl_construct(&ast);

    // Return the generated impl
    gen.parse().unwrap()
}

fn impl_construct(ast: &syn::DeriveInput) -> quote::Tokens {
    if let Body::Struct(ref body) = ast.body {
        let name = &ast.ident;
        let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();

        // Get field identifier and type for all struct fields.
        let fields: Vec<(_, Ty)> = if let &VariantData::Struct(ref fields) = body {
            fields.iter()
                .map(|field| (
                    field.ident.as_ref().unwrap(),
                    field.ty.clone(),
                )).collect()
        } else {
            panic!("Expected struct fields");
        };

        // Add constraints and compute offsets.
        let mut where_clause = where_clause.clone();
        let mut offsets = Tokens::new();
        let mut i = 0;
        let mut ns = vec![];
        for &(_, ref ty) in &fields {
            let ty_ident = if let &Ty::Path(_, ref parameters) = ty {
                parameters.segments[0].ident.clone()
            } else {
                panic!("Could not find type identifier.")
            };
            if ty_ident != &Ident::new("u64") {
                // Add `T: Construct` constraint.
                where_clause.predicates.push(WherePredicate::BoundPredicate(WhereBoundPredicate {
                    bound_lifetimes: vec![],
                    bounded_ty: ty.clone(),
                    bounds: vec![TyParamBound::Trait(PolyTraitRef {
                        bound_lifetimes: vec![],
                        trait_ref: Ident::new("Construct").into()
                    }, TraitBoundModifier::None)]
                }));
                offsets.append(
                    format!("let n{} = <{} as Construct>::n();", i, ty_ident)
                );
                i += 1;
            } else {
                ns.push(i);
            }
        }

        // Map arguments to struct fields.
        let mut field_tokens = Tokens::new();
        let mut i = 0;
        for &(ref field, ref ty) in &fields {
            field_tokens.append(field);
            field_tokens.append(":");
            let ty_ident = if let &Ty::Path(_, ref parameters) = ty {
                parameters.segments[0].ident.clone()
            } else {
                panic!("Could not find type identifier.")
            };
            if ty_ident == &Ident::new("u64") {
                field_tokens.append("vs[");
                if ns[i] != 0 {
                    field_tokens.append(format!("n{}+", ns[i]-1));
                }
                field_tokens.append(&format!("{}", i));
                field_tokens.append("]");
                i += 1;
            } else {
                field_tokens.append("Construct::construct(vs)");
            }
            field_tokens.append(",");
        }

        quote! {
            impl #impl_generics Construct for #name #ty_generics #where_clause {
                fn construct(vs: &[u64]) -> Self {
                    #offsets
                    #name {
                        #field_tokens
                    }
                }
            }
        }
    } else {panic!("Must be a struct.")}
}