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use either::Either;
use proc_macro2::TokenStream;
use quote::{quote, quote_spanned, ToTokens};
use syn::{
parse_macro_input, spanned::Spanned, Data, DataEnum, DataStruct, DataUnion, DeriveInput, Field,
Fields, GenericParam, Generics, Ident, ImplGenerics, Lit, Meta, MetaNameValue, Type,
TypeGenerics, WhereClause,
};
#[proc_macro_derive(TypeHash, attributes(type_hash))]
pub fn derive_type_hash(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let input = parse_macro_input!(input as DeriveInput);
type_hash_impl(input).into()
}
fn type_hash_impl(input: DeriveInput) -> TokenStream {
match &input.data {
Data::Struct(data) => type_hash_struct(&input.ident, &input.generics, data),
Data::Enum(data) => type_hash_enum(&input.ident, &input.generics, data),
Data::Union(data) => type_hash_union(&input.ident, data),
}
}
fn type_hash_struct(ident: &Ident, generics: &Generics, data: &DataStruct) -> TokenStream {
let name = ident.to_string();
let fields = write_field_hashes(&data.fields).into_iter().flatten();
let (impl_generics, ty_generics, where_clause) = split_generics(generics);
quote! {
impl#impl_generics type_hash::TypeHash for #ident#ty_generics #where_clause {
fn write_hash(hasher: &mut impl std::hash::Hasher) {
hasher.write(#name.as_bytes());
#(#fields)*
}
}
}
}
fn type_hash_enum(ident: &Ident, generics: &Generics, data: &DataEnum) -> TokenStream {
let name = ident.to_string();
let (impl_generics, ty_generics, where_clause) = split_generics(generics);
let variants = data.variants.iter().flat_map(|v| {
v.discriminant
.iter()
.map(|(_, discriminant)| {
quote! {
std::hash::Hash::hash(&(#discriminant as isize), hasher);
}
})
.chain(write_field_hashes(&v.fields).into_iter().flatten())
});
quote! {
impl#impl_generics type_hash::TypeHash for #ident#ty_generics #where_clause{
fn write_hash(hasher: &mut impl std::hash::Hasher) {
hasher.write(#name.as_bytes());
#(#variants)*
}
}
}
}
fn write_field_hashes(fields: &Fields) -> Option<impl Iterator<Item = TokenStream> + '_> {
match &fields {
Fields::Unit => None,
Fields::Named(fields) => {
Some(Either::Left(fields.named.iter().map(|f| {
match field_attrs(f) {
Ok(Some(tokens)) => tokens,
Ok(None) => TokenStream::new(),
Err(tokens) => tokens,
}
})))
}
Fields::Unnamed(fields) => Some(Either::Right(fields.unnamed.iter().map(|f| {
let field_type = f.ty.clone();
quote! {
<#field_type as type_hash::TypeHash>::write_hash(hasher);
}
}))),
}
}
fn field_attrs(field: &Field) -> Result<Option<TokenStream>, TokenStream> {
let field_name = field.ident.as_ref().unwrap().to_token_stream().to_string();
for att in &field.attrs {
if let Some(name) = att.path.get_ident() {
if name == "type_hash" {
match att.parse_args() {
Ok(Meta::NameValue(MetaNameValue { path, lit, .. })) => {
if let (Some(name), Lit::Str(val)) = (path.get_ident(), lit) {
if name == "as" {
if let Ok(ty) = val.parse::<Type>() {
return Ok(Some(quote! {
hasher.write(#field_name.as_bytes());
<#ty as type_hash::TypeHash>::write_hash(hasher);
}));
} else {
return Err(quote_spanned! {
val.span()=>
compile_error!("Invalid type");
});
}
}
}
return Err(quote_spanned! {
att.span()=>
compile_error!("Unsupported metadata");
});
}
Ok(Meta::Path(path)) => {
if let Some(name) = path.get_ident() {
if name == "skip" {
return Ok(None);
} else if name == "foreign_type" {
let type_str = field.ty.to_token_stream().to_string();
return Ok(Some(quote! {
hasher.write(#field_name.as_bytes());
hasher.write(#type_str.as_bytes());
}));
}
}
return Err(quote_spanned! {
name.span()=>
compile_error!("Unsupported metadata");
});
}
Ok(m) => {
return Err(quote_spanned! {
m.span()=>
compile_error!("Unsupported metadata");
});
}
Err(e) => {
let e = e.to_string();
return Err(quote_spanned! {
att.span()=>
compile_error!("{}", #e);
});
}
}
}
}
}
let field_type = &field.ty;
Ok(Some(quote! {
hasher.write(#field_name.as_bytes());
<#field_type as type_hash::TypeHash>::write_hash(hasher);
}))
}
fn type_hash_union(_ident: &Ident, data: &DataUnion) -> TokenStream {
quote_spanned! {
data.union_token.span()=>
compile_error!("Unions are not currently supported");
}
}
struct DeriveWhereClause<'a>(&'a Generics, Option<&'a WhereClause>);
impl<'a> ToTokens for DeriveWhereClause<'a> {
fn to_tokens(&self, tokens: &mut TokenStream) {
let generics = &self.0;
let mut predicates = self.1.iter().flat_map(|w| &w.predicates).peekable();
let mut params = generics
.params
.iter()
.filter_map(|param| {
if let GenericParam::Type(type_param) = param {
Some(&type_param.ident)
} else {
None
}
})
.peekable();
if params.peek().is_some() || predicates.next().is_some() {
let clause = quote! {
where #(#params: type_hash::TypeHash,)* #(#predicates,)*
};
clause.to_tokens(tokens);
}
}
}
fn split_generics(generics: &Generics) -> (ImplGenerics, TypeGenerics, DeriveWhereClause<'_>) {
let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
let where_clause = DeriveWhereClause(&generics, where_clause);
(impl_generics, ty_generics, where_clause)
}