educe/trait_handlers/default/
default_struct.rs

1use quote::quote;
2use syn::{Data, DeriveInput, Fields, Meta, Type};
3
4use super::{
5    models::{FieldAttributeBuilder, TypeAttributeBuilder},
6    TraitHandler,
7};
8use crate::Trait;
9
10pub(crate) struct DefaultStructHandler;
11
12impl TraitHandler for DefaultStructHandler {
13    fn trait_meta_handler(
14        ast: &DeriveInput,
15        token_stream: &mut proc_macro2::TokenStream,
16        traits: &[Trait],
17        meta: &Meta,
18    ) -> syn::Result<()> {
19        let type_attribute = TypeAttributeBuilder {
20            enable_flag:       true,
21            enable_new:        true,
22            enable_expression: true,
23            enable_bound:      true,
24        }
25        .build_from_default_meta(meta)?;
26
27        let mut default_types: Vec<&Type> = Vec::new();
28
29        let mut default_token_stream = proc_macro2::TokenStream::new();
30
31        if let Data::Struct(data) = &ast.data {
32            if let Some(expression) = type_attribute.expression {
33                for field in data.fields.iter() {
34                    let _ = FieldAttributeBuilder {
35                        enable_flag:       false,
36                        enable_expression: false,
37                    }
38                    .build_from_attributes(&field.attrs, traits, &field.ty)?;
39                }
40
41                default_token_stream.extend(quote!(#expression));
42            } else {
43                match &data.fields {
44                    Fields::Unit => {
45                        default_token_stream.extend(quote!(Self));
46                    },
47                    Fields::Named(_) => {
48                        let mut fields_token_stream = proc_macro2::TokenStream::new();
49
50                        for field in data.fields.iter() {
51                            let field_attribute = FieldAttributeBuilder {
52                                enable_flag:       false,
53                                enable_expression: true,
54                            }
55                            .build_from_attributes(&field.attrs, traits, &field.ty)?;
56
57                            let field_name = field.ident.as_ref().unwrap();
58
59                            if let Some(expression) = field_attribute.expression {
60                                fields_token_stream.extend(quote! {
61                                    #field_name: #expression,
62                                });
63                            } else {
64                                let ty = &field.ty;
65
66                                default_types.push(ty);
67
68                                fields_token_stream.extend(quote! {
69                                    #field_name: <#ty as ::core::default::Default>::default(),
70                                });
71                            }
72                        }
73
74                        default_token_stream.extend(quote! {
75                            Self {
76                                #fields_token_stream
77                            }
78                        });
79                    },
80                    Fields::Unnamed(_) => {
81                        let mut fields_token_stream = proc_macro2::TokenStream::new();
82
83                        for field in data.fields.iter() {
84                            let field_attribute = FieldAttributeBuilder {
85                                enable_flag:       false,
86                                enable_expression: true,
87                            }
88                            .build_from_attributes(&field.attrs, traits, &field.ty)?;
89
90                            if let Some(expression) = field_attribute.expression {
91                                fields_token_stream.extend(quote!(#expression,));
92                            } else {
93                                let ty = &field.ty;
94
95                                default_types.push(ty);
96
97                                fields_token_stream
98                                    .extend(quote!(<#ty as ::core::default::Default>::default(),));
99                            }
100                        }
101
102                        default_token_stream.extend(quote!(Self ( #fields_token_stream )));
103                    },
104                }
105            }
106        }
107
108        let ident = &ast.ident;
109
110        let bound = type_attribute.bound.into_where_predicates_by_generic_parameters_check_types(
111            &ast.generics.params,
112            &syn::parse2(quote!(::core::default::Default)).unwrap(),
113            &default_types,
114            &[],
115        );
116
117        let mut generics = ast.generics.clone();
118        let where_clause = generics.make_where_clause();
119
120        for where_predicate in bound {
121            where_clause.predicates.push(where_predicate);
122        }
123
124        let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
125
126        token_stream.extend(quote! {
127            impl #impl_generics ::core::default::Default for #ident #ty_generics #where_clause {
128                #[inline]
129                fn default() -> Self {
130                    #default_token_stream
131                }
132            }
133        });
134
135        if type_attribute.new {
136            token_stream.extend(quote! {
137                impl #impl_generics #ident #ty_generics #where_clause {
138                    /// Returns the "default value" for a type.
139                    #[inline]
140                    pub fn new() -> Self {
141                        <Self as ::core::default::Default>::default()
142                    }
143                }
144            });
145        }
146
147        Ok(())
148    }
149}
educe/trait_handlers/default/default_struct.rs

educe/trait_handlers/default/
default_struct.rs
