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extern crate proc_macro;
extern crate syn;
#[macro_use]
extern crate quote;
use proc_macro::TokenStream;
use syn::fold::Folder;
use syn::fold::noop_fold_generics;
use syn::fold::noop_fold_path;
use syn::AngleBracketedParameterData;
use syn::Generics;
use syn::Ident;
use syn::Lifetime;
use syn::Path;
use syn::PathParameters;
use syn::PathSegment;
use syn::PolyTraitRef;
use syn::TraitBoundModifier;
use syn::Ty;
use syn::TyParam;
use syn::TyParamBound;
use syn::WhereClause;
#[proc_macro_derive(RoundTrip)]
pub fn round_trip(input: TokenStream) -> TokenStream {
let s = input.to_string();
let ast = syn::parse_macro_input(&s).unwrap();
let gen = impl_round_trip(&ast);
gen.parse().unwrap()
}
struct Renaming<'a> {
original: &'a Generics,
lifetime_prefix: &'a str,
ty_param_prefix: &'a str,
}
impl<'a> Folder for Renaming<'a> {
fn fold_generics(&mut self, generics: Generics) -> Generics {
let mut result = noop_fold_generics(self, generics);
for ty_param in &mut result.ty_params {
ty_param.ident = self.fold_ty_param_ident(ty_param.ident.clone());
}
result
}
fn fold_lifetime(&mut self, lifetime: Lifetime) -> Lifetime {
Lifetime { ident: self.fold_lifetime_ident(lifetime.ident) }
}
fn fold_path(&mut self, path: Path) -> Path {
let mut result = noop_fold_path(self, path);
if let Some((segment, rest)) = result.segments.split_first_mut() {
if rest.is_empty() && segment.parameters.is_empty() {
segment.ident = self.fold_ty_param_ident(segment.ident.clone());
}
}
result
}
}
impl<'a> Renaming<'a> {
fn fold_lifetime_ident(&mut self, ident: Ident) -> Ident {
self.original.lifetimes.iter()
.position(|original| original.lifetime.ident == ident)
.map(|index| syn::Ident::from(format!("{}{}", self.lifetime_prefix, index)))
.unwrap_or(ident)
}
fn fold_ty_param_ident(&mut self, ident: Ident) -> Ident {
self.original.ty_params.iter()
.position(|original| original.ident == ident)
.map(|index| syn::Ident::from(format!("{}{}", self.ty_param_prefix, index)))
.unwrap_or(ident)
}
}
fn generic_path(ident: &Ident, generics: &Generics) -> Path {
Path {
global: false,
segments: vec![ PathSegment {
ident: ident.clone(),
parameters: PathParameters::AngleBracketed(AngleBracketedParameterData {
lifetimes: generics.lifetimes.iter()
.map(|lifetime_def| lifetime_def.lifetime.clone())
.collect(),
types: generics.ty_params.iter()
.map(|ty_param| Ty::Path(None, Path::from(ty_param.ident.clone())))
.collect(),
bindings: vec![],
}),
} ]
}
}
fn ty_param_bound(text: &str) -> TyParamBound {
TyParamBound::Trait(
PolyTraitRef {
bound_lifetimes: vec![],
trait_ref: syn::parse::path(text).expect("Unexpected parse error"),
},
TraitBoundModifier::None,
)
}
fn impl_round_trip(ast: &syn::MacroInput) -> quote::Tokens {
let name = &ast.ident;
let mut target_renaming = Renaming { original: &ast.generics, lifetime_prefix: "'b", ty_param_prefix: "T" };
let mut target_generics = target_renaming.fold_generics(ast.generics.clone());
for ty_param in target_generics.ty_params.iter_mut() {
ty_param.bounds.push(ty_param_bound("::serde::Deserialize"));
}
let target_where_clause = target_generics.where_clause.clone();
let target_path = generic_path(&ast.ident, &target_generics);
let target_ty_param_bound = quote! { ::serde_roundtrip::SameDeserialization<SameAs=#target_path> };
let target_ty_param = TyParam {
attrs: vec![],
ident: Ident::from("T"),
bounds: vec![ty_param_bound(target_ty_param_bound.as_str())],
default: None,
};
let mut source_renaming = Renaming { original: &ast.generics, lifetime_prefix: "'a", ty_param_prefix: "S" };
let mut source_generics = source_renaming.fold_generics(ast.generics.clone());
for (ty_param, target_ty_param) in source_generics.ty_params.iter_mut().zip(target_generics.ty_params.iter()) {
let target_ty_param_ident = &target_ty_param.ident;
let text = quote! { ::serde_roundtrip::RoundTrip<#target_ty_param_ident> };
ty_param.bounds.push(ty_param_bound(text.as_str()));
}
let source_path = generic_path(&ast.ident, &source_generics);
let all_generics = Generics {
lifetimes: source_generics.lifetimes.iter().cloned()
.chain(target_generics.lifetimes.iter().cloned())
.collect::<Vec<_>>(),
ty_params: source_generics.ty_params.iter().cloned()
.chain(target_generics.ty_params.iter().cloned())
.chain(::std::iter::once(target_ty_param))
.collect::<Vec<_>>(),
where_clause: WhereClause {
predicates: source_generics.where_clause.predicates.iter().cloned()
.chain(target_generics.where_clause.predicates.iter().cloned())
.collect::<Vec<_>>(),
},
};
let all_where_clause = all_generics.where_clause.clone();
let round_trip = match ast.body {
syn::Body::Struct(syn::VariantData::Struct(ref body)) => {
let fields = body.iter()
.filter_map(|field| field.ident.as_ref())
.map(|ident| quote! { #ident: self.#ident.round_trip() })
.collect::<Vec<_>>();
quote! { #name { #(#fields),* } }
},
syn::Body::Struct(syn::VariantData::Tuple(ref body)) => {
let fields = (0..body.len())
.map(syn::Ident::from)
.map(|index| quote! { self.#index.round_trip() })
.collect::<Vec<_>>();
quote! { #name ( #(#fields),* ) }
},
syn::Body::Struct(syn::VariantData::Unit) => {
quote! { #name }
},
syn::Body::Enum(ref body) => {
let cases = body.iter()
.map(|case| {
let unqualified_ident = &case.ident;
let ident = quote! { #name::#unqualified_ident };
match case.data {
syn::VariantData::Struct(ref body) => {
let idents = body.iter()
.filter_map(|field| field.ident.as_ref())
.collect::<Vec<_>>();;
let cloned = idents.iter()
.map(|ident| quote! { #ident: #ident.round_trip() })
.collect::<Vec<_>>();
quote! { #ident { #(ref #idents),* } => #ident { #(#cloned),* } }
},
syn::VariantData::Tuple(ref body) => {
let idents = (0..body.len())
.map(|index| syn::Ident::from(format!("x{}", index)))
.collect::<Vec<_>>();
let cloned = idents.iter()
.map(|ident| quote! { #ident.round_trip() })
.collect::<Vec<_>>();
quote! { #ident ( #(ref #idents),* ) => #ident ( #(#cloned),* ) }
},
syn::VariantData::Unit => {
quote! { #ident => #ident }
},
}
})
.collect::<Vec<_>>();
quote! { match *self { #(#cases),* } }
},
};
quote! {
impl #all_generics ::serde_roundtrip::RoundTrip<T> for #source_path
#all_where_clause
{
fn round_trip(&self) -> T { T::from(#round_trip) }
}
impl #target_generics ::serde_roundtrip::SameDeserialization for #target_path
#target_where_clause
{
type SameAs = Self;
fn from(data: Self) -> Self { data }
}
}
}