educe/trait_handlers/deref/
deref_struct.rs

1use quote::quote;
2use syn::{spanned::Spanned, Data, DeriveInput, Field, Meta};
3
4use super::{
5    models::{FieldAttributeBuilder, TypeAttributeBuilder},
6    TraitHandler,
7};
8use crate::{
9    common::{ident_index::IdentOrIndex, r#type::dereference_changed},
10    Trait,
11};
12
13pub(crate) struct DerefStructHandler;
14
15impl TraitHandler for DerefStructHandler {
16    #[inline]
17    fn trait_meta_handler(
18        ast: &DeriveInput,
19        token_stream: &mut proc_macro2::TokenStream,
20        traits: &[Trait],
21        meta: &Meta,
22    ) -> syn::Result<()> {
23        let _ = TypeAttributeBuilder {
24            enable_flag: true
25        }
26        .build_from_deref_meta(meta)?;
27
28        let mut target_token_stream = proc_macro2::TokenStream::new();
29        let mut deref_token_stream = proc_macro2::TokenStream::new();
30
31        if let Data::Struct(data) = &ast.data {
32            let (index, field) = {
33                let fields = &data.fields;
34
35                if fields.len() == 1 {
36                    let field = fields.into_iter().next().unwrap();
37
38                    let _ = FieldAttributeBuilder {
39                        enable_flag: true
40                    }
41                    .build_from_attributes(&field.attrs, traits)?;
42
43                    (0usize, field)
44                } else {
45                    let mut deref_field: Option<(usize, &Field)> = None;
46
47                    for (index, field) in fields.iter().enumerate() {
48                        let field_attribute = FieldAttributeBuilder {
49                            enable_flag: true
50                        }
51                        .build_from_attributes(&field.attrs, traits)?;
52
53                        if field_attribute.flag {
54                            if deref_field.is_some() {
55                                return Err(super::panic::multiple_deref_fields(
56                                    field_attribute.span,
57                                ));
58                            }
59
60                            deref_field = Some((index, field));
61                        }
62                    }
63
64                    if let Some(deref_field) = deref_field {
65                        deref_field
66                    } else {
67                        return Err(super::panic::no_deref_field(meta.span()));
68                    }
69                }
70            };
71
72            let ty = &field.ty;
73            let (dereference_ty, is_ref) = dereference_changed(ty);
74
75            target_token_stream.extend(quote!(#dereference_ty));
76
77            let field_name = IdentOrIndex::from_ident_with_index(field.ident.as_ref(), index);
78
79            deref_token_stream.extend(if is_ref {
80                quote! (self.#field_name)
81            } else {
82                quote! (&self.#field_name)
83            });
84        }
85
86        let ident = &ast.ident;
87
88        let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
89
90        token_stream.extend(quote! {
91            impl #impl_generics ::core::ops::Deref for #ident #ty_generics #where_clause {
92                type Target = #target_token_stream;
93
94                #[inline]
95                fn deref(&self) -> &Self::Target {
96                    #deref_token_stream
97                }
98            }
99        });
100
101        Ok(())
102    }
103}
educe/trait_handlers/deref/deref_struct.rs

educe/trait_handlers/deref/
deref_struct.rs
