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
#![cfg_attr(feature="clippy", feature(plugin))]
#![cfg_attr(feature="clippy", plugin(clippy))]
extern crate proc_macro;
extern crate syn;
#[macro_use]
extern crate quote;
use proc_macro::TokenStream;
fn filter_primitive_type_attr(attr: &syn::Attribute) -> Option<&str> {
use syn::MetaItem::NameValue;
match attr.value {
NameValue(ref ident, syn::Lit::Str(ref value, _)) => {
if ident == "TryFromPrimitiveType" {
Some(value)
} else {
None
}
},
_ => None,
}
}
fn impl_single_type<'a, I: Iterator<Item=&'a syn::Variant>>
(name: &syn::Ident, ty: &syn::Ident, variants: I) -> quote::Tokens {
let blocks = variants.map(|var| {
let ident = &var.ident;
if var.data != syn::VariantData::Unit {
panic!("Enum variant may not store data!")
}
quote!{
if v == #name::#ident as #ty {
Ok(#name::#ident)
}
}
});
let mut tokens = quote::Tokens::new();
tokens.append_separated(blocks, "else");
quote! {
impl TryFrom<#ty> for #name {
type Error = enum_tryfrom::InvalidEnumValue;
fn try_from(v: #ty) -> Result<Self, Self::Error> {
#tokens else {
Err(Self::Error::new())
}
}
}
}
}
fn impl_from_primitive(ast: &syn::DeriveInput) -> quote::Tokens {
let name = &ast.ident;
let types = ast.attrs.iter().filter_map(filter_primitive_type_attr)
.map(syn::Ident::new);
let variants =
if let syn::Body::Enum(ref variants) = ast.body {
variants
} else {
panic!("`TryFromPrimitive` is only supported on Enums")
};
let impls = types.map(|ty| impl_single_type(name, &ty, variants.iter()));
let mut tokens = quote::Tokens::new();
tokens.append_all(impls);
tokens
}
#[proc_macro_derive(TryFromPrimitive, attributes(TryFromPrimitiveType))]
pub fn from_primitive(input: TokenStream) -> TokenStream {
let s = input.to_string();
let ast = syn::parse_derive_input(&s).unwrap();
let gen = impl_from_primitive(&ast);
gen.parse().unwrap()
}