serde_derive/
pretend.rs

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
180
181
182
183
184
185
use crate::internals::ast::{Container, Data, Field, Style, Variant};
use proc_macro2::TokenStream;
use quote::{format_ident, quote};

// Suppress dead_code warnings that would otherwise appear when using a remote
// derive. Other than this pretend code, a struct annotated with remote derive
// never has its fields referenced and an enum annotated with remote derive
// never has its variants constructed.
//
//     warning: field is never used: `i`
//      --> src/main.rs:4:20
//       |
//     4 | struct StructDef { i: i32 }
//       |                    ^^^^^^
//
//     warning: variant is never constructed: `V`
//      --> src/main.rs:8:16
//       |
//     8 | enum EnumDef { V }
//       |                ^
//
pub fn pretend_used(cont: &Container, is_packed: bool) -> TokenStream {
    let pretend_fields = pretend_fields_used(cont, is_packed);
    let pretend_variants = pretend_variants_used(cont);

    quote! {
        #pretend_fields
        #pretend_variants
    }
}

// For structs with named fields, expands to:
//
//     match None::<&T> {
//         Some(T { a: __v0, b: __v1 }) => {}
//         _ => {}
//     }
//
// For packed structs on sufficiently new rustc, expands to:
//
//     match None::<&T> {
//         Some(__v @ T { a: _, b: _ }) => {
//             let _ = addr_of!(__v.a);
//             let _ = addr_of!(__v.b);
//         }
//         _ => {}
//     }
//
// For packed structs on older rustc, we assume Sized and !Drop, and expand to:
//
//     match None::<T> {
//         Some(T { a: __v0, b: __v1 }) => {}
//         _ => {}
//     }
//
// For enums, expands to the following but only including struct variants:
//
//     match None::<&T> {
//         Some(T::A { a: __v0 }) => {}
//         Some(T::B { b: __v0 }) => {}
//         _ => {}
//     }
//
fn pretend_fields_used(cont: &Container, is_packed: bool) -> TokenStream {
    match &cont.data {
        Data::Enum(variants) => pretend_fields_used_enum(cont, variants),
        Data::Struct(Style::Struct | Style::Tuple | Style::Newtype, fields) => {
            if is_packed {
                pretend_fields_used_struct_packed(cont, fields)
            } else {
                pretend_fields_used_struct(cont, fields)
            }
        }
        Data::Struct(Style::Unit, _) => quote!(),
    }
}

fn pretend_fields_used_struct(cont: &Container, fields: &[Field]) -> TokenStream {
    let type_ident = &cont.ident;
    let (_, ty_generics, _) = cont.generics.split_for_impl();

    let members = fields.iter().map(|field| &field.member);
    let placeholders = (0usize..).map(|i| format_ident!("__v{}", i));

    quote! {
        match _serde::__private::None::<&#type_ident #ty_generics> {
            _serde::__private::Some(#type_ident { #(#members: #placeholders),* }) => {}
            _ => {}
        }
    }
}

fn pretend_fields_used_struct_packed(cont: &Container, fields: &[Field]) -> TokenStream {
    let type_ident = &cont.ident;
    let (_, ty_generics, _) = cont.generics.split_for_impl();

    let members = fields.iter().map(|field| &field.member).collect::<Vec<_>>();

    quote! {
        match _serde::__private::None::<&#type_ident #ty_generics> {
            _serde::__private::Some(__v @ #type_ident { #(#members: _),* }) => {
                #(
                    let _ = _serde::__private::ptr::addr_of!(__v.#members);
                )*
            }
            _ => {}
        }
    }
}

fn pretend_fields_used_enum(cont: &Container, variants: &[Variant]) -> TokenStream {
    let type_ident = &cont.ident;
    let (_, ty_generics, _) = cont.generics.split_for_impl();

    let patterns = variants
        .iter()
        .filter_map(|variant| match variant.style {
            Style::Struct | Style::Tuple | Style::Newtype => {
                let variant_ident = &variant.ident;
                let members = variant.fields.iter().map(|field| &field.member);
                let placeholders = (0usize..).map(|i| format_ident!("__v{}", i));
                Some(quote!(#type_ident::#variant_ident { #(#members: #placeholders),* }))
            }
            Style::Unit => None,
        })
        .collect::<Vec<_>>();

    quote! {
        match _serde::__private::None::<&#type_ident #ty_generics> {
            #(
                _serde::__private::Some(#patterns) => {}
            )*
            _ => {}
        }
    }
}

// Expands to one of these per enum variant:
//
//     match None {
//         Some((__v0, __v1,)) => {
//             let _ = E::V { a: __v0, b: __v1 };
//         }
//         _ => {}
//     }
//
fn pretend_variants_used(cont: &Container) -> TokenStream {
    let variants = match &cont.data {
        Data::Enum(variants) => variants,
        Data::Struct(_, _) => {
            return quote!();
        }
    };

    let type_ident = &cont.ident;
    let (_, ty_generics, _) = cont.generics.split_for_impl();
    let turbofish = ty_generics.as_turbofish();

    let cases = variants.iter().map(|variant| {
        let variant_ident = &variant.ident;
        let placeholders = &(0..variant.fields.len())
            .map(|i| format_ident!("__v{}", i))
            .collect::<Vec<_>>();

        let pat = match variant.style {
            Style::Struct => {
                let members = variant.fields.iter().map(|field| &field.member);
                quote!({ #(#members: #placeholders),* })
            }
            Style::Tuple | Style::Newtype => quote!(( #(#placeholders),* )),
            Style::Unit => quote!(),
        };

        quote! {
            match _serde::__private::None {
                _serde::__private::Some((#(#placeholders,)*)) => {
                    let _ = #type_ident::#variant_ident #turbofish #pat;
                }
                _ => {}
            }
        }
    });

    quote!(#(#cases)*)
}