darling_core/codegen/
attrs_field.rs

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1use quote::{quote, quote_spanned, ToTokens, TokenStreamExt};
2use syn::spanned::Spanned;
3
4use crate::options::{AttrsField, ForwardAttrsFilter};
5
6#[derive(Default)]
7pub struct ForwardAttrs<'a> {
8    pub filter: Option<&'a ForwardAttrsFilter>,
9    pub field: Option<&'a AttrsField>,
10}
11
12impl ForwardAttrs<'_> {
13    /// Check if this will forward any attributes; this requires both that
14    /// there be a filter which can match some attributes and a field to receive them.
15    pub fn will_forward_any(&self) -> bool {
16        if let Some(filter) = self.filter {
17            !filter.is_empty() && self.field.is_some()
18        } else {
19            false
20        }
21    }
22
23    /// Get the field declarations to support attribute forwarding
24    pub fn as_declaration(&self) -> Option<Declaration<'_>> {
25        self.field.map(Declaration)
26    }
27
28    /// Get the match arms for attribute matching
29    pub fn as_match_arms(&self) -> MatchArms<'_> {
30        MatchArms(self)
31    }
32
33    /// Get the statement that will try to transform forwarded attributes into
34    /// the result expected by the receiver field.
35    pub fn as_value_populator(&self) -> Option<ValuePopulator<'_>> {
36        self.field.map(ValuePopulator)
37    }
38
39    /// Get the field initializer for use when building the deriving struct.
40    pub fn as_initializer(&self) -> Option<Initializer<'_>> {
41        self.field.map(Initializer)
42    }
43}
44
45pub struct Declaration<'a>(pub &'a AttrsField);
46
47impl ToTokens for Declaration<'_> {
48    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
49        let ident = &self.0.ident;
50        tokens.append_all(quote! {
51            let mut __fwd_attrs: ::darling::export::Vec<::darling::export::syn::Attribute> = vec![];
52            let mut #ident: ::darling::export::Option<_> = None;
53        });
54    }
55}
56
57pub struct ValuePopulator<'a>(pub &'a AttrsField);
58
59impl ToTokens for ValuePopulator<'_> {
60    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
61        let AttrsField { ident, with } = self.0;
62        let initializer_expr = match with {
63            Some(with) => quote_spanned!(with.span()=> __errors.handle(#with(__fwd_attrs))),
64            None => quote!(::darling::export::Some(__fwd_attrs)),
65        };
66        tokens.append_all(quote!(#ident = #initializer_expr;));
67    }
68}
69
70pub struct Initializer<'a>(pub &'a AttrsField);
71
72impl ToTokens for Initializer<'_> {
73    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
74        let ident = &self.0.ident;
75        tokens.append_all(quote!(#ident: #ident.expect("Errors were already checked"),));
76    }
77}
78
79pub struct MatchArms<'a>(&'a ForwardAttrs<'a>);
80
81impl ToTokens for MatchArms<'_> {
82    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
83        if !self.0.will_forward_any() {
84            tokens.append_all(quote!(_ => continue));
85            return;
86        }
87
88        let push_command = quote!(__fwd_attrs.push(__attr.clone()));
89
90        tokens.append_all(
91            match self
92                .0
93                .filter
94                .expect("Can only forward attributes if filter is defined")
95            {
96                ForwardAttrsFilter::All => quote!(_ => #push_command),
97                ForwardAttrsFilter::Only(idents) => {
98                    let names = idents.to_strings();
99                    quote! {
100                        #(#names)|* => #push_command,
101                        _ => continue,
102                    }
103                }
104            },
105        );
106    }
107}
darling_core/codegen/attrs_field.rs

darling_core/codegen/
attrs_field.rs
