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
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
|
#![deny(clippy::use_self)]
#[proc_macro_derive(Get, attributes(get))]
pub fn get(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let parsed_input = syn::parse_macro_input!(input as syn::DeriveInput);
get::expand(&parsed_input, false).unwrap().into()
}
mod get {
use proc_macro2::{Span, TokenStream};
use quote::{format_ident, quote, ToTokens};
use syn::{
parse::Parser, punctuated::Punctuated, Attribute, Data, DeriveInput, Expr, Field, Fields,
Index, Lit, Member, Meta, MetaNameValue, Token, Type,
};
#[derive(Default)]
struct GetAttribute {
method: Option<String>,
}
#[derive(Debug, Clone)]
enum GetNameValue {
Method(String),
}
pub fn expand(
input: &DeriveInput,
is_copy: bool,
) -> Result<TokenStream, Box<dyn std::error::Error>> {
let Data::Struct(target) = &input.data else {
return Err("expected struct as derive input".into())
};
let getters = match &target.fields {
Fields::Unnamed(fields) => expand_for_tuple_struct(fields.unnamed.iter(), is_copy)?,
Fields::Named(fields) => expand_for_struct(fields.named.iter(), is_copy)?,
_ => return Err("can not generate getters on a unit struct".into()),
};
let (impl_generics, ty_generics, where_clause) = &input.generics.split_for_impl();
let struct_name = &input.ident;
Ok(quote! {
#[automatically_derived]
impl #impl_generics #struct_name #ty_generics #where_clause {
#getters
}
})
}
fn expand_for_struct<'a>(
fields: impl Iterator<Item = &'a Field>,
is_copy: bool,
) -> Result<TokenStream, Box<dyn std::error::Error>> {
let mut tokens = TokenStream::new();
for field in fields {
let default_method_name = field.ident.as_ref().cloned().unwrap().to_string();
let method_name = field
.attrs
.iter()
.find(|attr| attr.path().is_ident("get"))
.cloned()
.map_or(Ok(default_method_name.clone()), |attr| {
GetAttribute::try_from(attr)
.map(|get_attr| get_attr.method.unwrap_or(default_method_name.clone()))
})?;
let getter = expand_getter(
field,
Member::Named(field.ident.as_ref().unwrap().clone()),
method_name.as_str(),
is_copy,
);
getter.to_tokens(&mut tokens);
}
Ok(tokens)
}
fn expand_for_tuple_struct<'a>(
fields: impl Iterator<Item = &'a Field>,
is_copy: bool,
) -> Result<TokenStream, Box<dyn std::error::Error>> {
let mut tokens = TokenStream::new();
for (i, field) in fields.enumerate() {
let attr: GetAttribute = field
.attrs
.iter()
.find(|a| a.path().is_ident("get"))
.cloned()
.ok_or("tuple fields are required to have an attribute")?
.try_into()?;
let method_name = attr
.method
.ok_or("tuple field attributes must specify the method name")?;
let getter = expand_getter(
field,
Member::Unnamed(Index {
index: i as u32,
span: Span::call_site(),
}),
method_name.as_str(),
is_copy,
);
getter.to_tokens(&mut tokens);
}
Ok(tokens)
}
fn expand_getter(
field: &Field,
field_name: Member,
method_name: &str,
is_copy: bool,
) -> TokenStream {
let method_name = format_ident!("{method_name}");
let field_type = &field.ty;
let field_lifetime = match &field.ty {
Type::Reference(type_ref) => Some(&type_ref.lifetime),
_ => None,
};
let reference = (!is_copy).then(|| quote! { & });
quote! {
pub fn
#method_name
( #reference #field_lifetime self )
-> #reference #field_type {
#reference self.#field_name
}
}
}
// This method might seem overly complicated but it will make it easy to add new fields to the
// GetAttribute struct in the future!
impl TryFrom<Attribute> for GetAttribute {
type Error = Box<dyn std::error::Error>;
fn try_from(attr: Attribute) -> Result<Self, Self::Error> {
if attr.path().is_ident("get") {
if let Meta::List(meta_list) = &attr.meta {
if let Ok(meta_name_values) =
Punctuated::<MetaNameValue, Token![,]>::parse_terminated
.parse(meta_list.tokens.clone().into())
{
let get_name_values = meta_name_values
.iter()
.map(|n| n.try_into())
.collect::<Result<Vec<GetNameValue>, _>>()?;
if let 1..=3 = get_name_values.len() {
return Ok(get_name_values.into_iter().fold(
Self::default(),
|_, g| match g {
GetNameValue::Method(name) => Self { method: Some(name) },
},
));
}
}
}
}
Err("failed to parse attribute".into())
}
}
// The same applies here.
impl<'a> TryFrom<&'a MetaNameValue> for GetNameValue {
type Error = Box<dyn std::error::Error>;
fn try_from(meta: &'a MetaNameValue) -> Result<Self, Self::Error> {
if let Some(name) = meta.path.get_ident().map(|i| i.to_string()) {
if let Expr::Lit(expr_lit) = &meta.value {
if let Lit::Str(s) = &expr_lit.lit {
let value = s.value();
if let "method" = name.as_str() {
return Ok(Self::Method(value));
};
}
}
}
Err("invalid name value list in attribute".into())
}
}
}
|
