openethereum/crates/util/rlp-derive/src/de.rs

// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of OpenEthereum.

// OpenEthereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// OpenEthereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with OpenEthereum.  If not, see <http://www.gnu.org/licenses/>.

use proc_macro2::{Span, TokenStream};
use syn;

struct ParseQuotes {
    single: TokenStream,
    list: TokenStream,
    takes_index: bool,
}

fn decodable_parse_quotes() -> ParseQuotes {
    ParseQuotes {
        single: quote! { rlp.val_at },
        list: quote! { rlp.list_at },
        takes_index: true,
    }
}

fn decodable_wrapper_parse_quotes() -> ParseQuotes {
    ParseQuotes {
        single: quote! { rlp.as_val },
        list: quote! { rlp.as_list },
        takes_index: false,
    }
}

pub fn impl_decodable(ast: &syn::DeriveInput) -> TokenStream {
    let body = match ast.data {
        syn::Data::Struct(ref s) => s,
        _ => panic!("#[derive(RlpDecodable)] is only defined for structs."),
    };

    let stmts: Vec<_> = body
        .fields
        .iter()
        .enumerate()
        .map(decodable_field_map)
        .collect();
    let name = &ast.ident;

    let dummy_const = syn::Ident::new(
        &format!("_IMPL_RLP_DECODABLE_FOR_{}", name),
        Span::call_site(),
    );
    let impl_block = quote! {
        impl rlp::Decodable for #name {
            fn decode(rlp: &rlp::Rlp) -> Result<Self, rlp::DecoderError> {
                let result = #name {
                    #(#stmts)*
                };

                Ok(result)
            }
        }
    };

    quote! {
        #[allow(non_upper_case_globals, unused_attributes, unused_qualifications)]
        const #dummy_const: () = {
            extern crate rlp;
            #impl_block
        };
    }
}

pub fn impl_decodable_wrapper(ast: &syn::DeriveInput) -> TokenStream {
    let body = match ast.data {
        syn::Data::Struct(ref s) => s,
        _ => panic!("#[derive(RlpDecodableWrapper)] is only defined for structs."),
    };

    let stmt = {
        let fields: Vec<_> = body.fields.iter().collect();
        if fields.len() == 1 {
            let field = fields.first().expect("fields.len() == 1; qed");
            decodable_field(0, field, decodable_wrapper_parse_quotes())
        } else {
            panic!("#[derive(RlpEncodableWrapper)] is only defined for structs with one field.")
        }
    };

    let name = &ast.ident;

    let dummy_const = syn::Ident::new(
        &format!("_IMPL_RLP_DECODABLE_FOR_{}", name),
        Span::call_site(),
    );
    let impl_block = quote! {
        impl rlp::Decodable for #name {
            fn decode(rlp: &rlp::Rlp) -> Result<Self, rlp::DecoderError> {
                let result = #name {
                    #stmt
                };

                Ok(result)
            }
        }
    };

    quote! {
        #[allow(non_upper_case_globals, unused_attributes, unused_qualifications)]
        const #dummy_const: () = {
            extern crate rlp;
            #impl_block
        };
    }
}

fn decodable_field_map(tuple: (usize, &syn::Field)) -> TokenStream {
    decodable_field(tuple.0, tuple.1, decodable_parse_quotes())
}

fn decodable_field(index: usize, field: &syn::Field, quotes: ParseQuotes) -> TokenStream {
    let id = match field.ident {
        Some(ref ident) => quote! { #ident },
        None => {
            let index: syn::Index = index.into();
            quote! { #index }
        }
    };

    let index = quote! { #index };

    let single = quotes.single;
    let list = quotes.list;

    match field.ty {
        syn::Type::Path(ref path) => {
            let ident = &path
                .path
                .segments
                .first()
                .expect("there must be at least 1 segment")
                .value()
                .ident;
            if &ident.to_string() == "Vec" {
                if quotes.takes_index {
                    quote! { #id: #list(#index)?, }
                } else {
                    quote! { #id: #list()?, }
                }
            } else {
                if quotes.takes_index {
                    quote! { #id: #single(#index)?, }
                } else {
                    quote! { #id: #single()?, }
                }
            }
        }
        _ => panic!("rlp_derive not supported"),
    }
}