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
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,
Fields, GenericParam, Generics, Ident, ImplGenerics, TypeGenerics, WhereClause,
};
#[proc_macro_derive(TypeHash)]
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| {
let field_name = f.ident.as_ref().unwrap().to_string();
let field_type = &f.ty;
quote! {
hasher.write(#field_name.as_bytes());
<#field_type as type_hash::TypeHash>::write_hash(hasher);
}
})))
}
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 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)
}