educe/trait_handlers/deref/
deref_enum.rs

1use quote::{format_ident, quote};
2use syn::{spanned::Spanned, Data, DeriveInput, Field, Fields, Ident, Meta, Type};
3
4use super::{
5    models::{FieldAttributeBuilder, TypeAttributeBuilder},
6    TraitHandler,
7};
8use crate::{common::r#type::dereference, panic, supported_traits::Trait};
9
10pub(crate) struct DerefEnumHandler;
11
12impl TraitHandler for DerefEnumHandler {
13    #[inline]
14    fn trait_meta_handler(
15        ast: &DeriveInput,
16        token_stream: &mut proc_macro2::TokenStream,
17        traits: &[Trait],
18        meta: &Meta,
19    ) -> syn::Result<()> {
20        let _ = TypeAttributeBuilder {
21            enable_flag: true
22        }
23        .build_from_deref_meta(meta)?;
24
25        let mut target_token_stream = proc_macro2::TokenStream::new();
26        let mut arms_token_stream = proc_macro2::TokenStream::new();
27
28        if let Data::Enum(data) = &ast.data {
29            type Variants<'a> = Vec<(&'a Ident, bool, usize, Ident, &'a Type)>;
30
31            let mut variants: Variants = Vec::new();
32
33            for variant in data.variants.iter() {
34                let _ = TypeAttributeBuilder {
35                    enable_flag: false
36                }
37                .build_from_attributes(&variant.attrs, traits)?;
38
39                if let Fields::Unit = &variant.fields {
40                    return Err(panic::trait_not_support_unit_variant(
41                        meta.path().get_ident().unwrap(),
42                        variant,
43                    ));
44                }
45
46                let fields = &variant.fields;
47
48                let (index, field) = if fields.len() == 1 {
49                    let field = fields.into_iter().next().unwrap();
50
51                    let _ = FieldAttributeBuilder {
52                        enable_flag: true
53                    }
54                    .build_from_attributes(&field.attrs, traits)?;
55
56                    (0usize, field)
57                } else {
58                    let mut deref_field: Option<(usize, &Field)> = None;
59
60                    for (index, field) in variant.fields.iter().enumerate() {
61                        let field_attribute = FieldAttributeBuilder {
62                            enable_flag: true
63                        }
64                        .build_from_attributes(&field.attrs, traits)?;
65
66                        if field_attribute.flag {
67                            if deref_field.is_some() {
68                                return Err(super::panic::multiple_deref_fields_of_variant(
69                                    field_attribute.span,
70                                    variant,
71                                ));
72                            }
73
74                            deref_field = Some((index, field));
75                        }
76                    }
77
78                    if let Some(deref_field) = deref_field {
79                        deref_field
80                    } else {
81                        return Err(super::panic::no_deref_field_of_variant(meta.span(), variant));
82                    }
83                };
84
85                let (field_name, is_tuple): (Ident, bool) = match field.ident.as_ref() {
86                    Some(ident) => (ident.clone(), false),
87                    None => (format_ident!("_{}", index), true),
88                };
89
90                variants.push((&variant.ident, is_tuple, index, field_name, &field.ty));
91            }
92
93            if variants.is_empty() {
94                return Err(super::panic::no_deref_field(meta.span()));
95            }
96
97            let ty = variants[0].4;
98            let dereference_ty = dereference(ty);
99
100            target_token_stream.extend(quote!(#dereference_ty));
101
102            for (variant_ident, is_tuple, index, field_name, _) in variants {
103                let mut pattern_token_stream = proc_macro2::TokenStream::new();
104
105                if is_tuple {
106                    for _ in 0..index {
107                        pattern_token_stream.extend(quote!(_,));
108                    }
109
110                    pattern_token_stream.extend(quote!( #field_name, .. ));
111
112                    arms_token_stream.extend(
113                        quote!( Self::#variant_ident ( #pattern_token_stream ) => #field_name, ),
114                    );
115                } else {
116                    pattern_token_stream.extend(quote!( #field_name, .. ));
117
118                    arms_token_stream.extend(
119                        quote!( Self::#variant_ident { #pattern_token_stream } => #field_name, ),
120                    );
121                }
122            }
123        }
124
125        let ident = &ast.ident;
126
127        let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
128
129        token_stream.extend(quote! {
130            impl #impl_generics ::core::ops::Deref for #ident #ty_generics #where_clause {
131                type Target = #target_token_stream;
132
133                #[inline]
134                fn deref(&self) -> &Self::Target {
135                    match self {
136                        #arms_token_stream
137                    }
138                }
139            }
140        });
141
142        Ok(())
143    }
144}
educe/trait_handlers/deref/deref_enum.rs

educe/trait_handlers/deref/
deref_enum.rs
