darling_core/codegen/
attrs_field.rs

1use quote::{quote, quote_spanned, ToTokens, TokenStreamExt};
2use syn::spanned::Spanned;
3
4use crate::options::{ForwardAttrsFilter, ForwardedField};
5
6#[derive(Default)]
7pub struct ForwardAttrs<'a> {
8    pub filter: Option<&'a ForwardAttrsFilter>,
9    pub field: Option<&'a ForwardedField>,
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<'a>(&'a self) -> Option<impl 'a + ToTokens> {
41        self.field.map(|f| f.as_initializer())
42    }
43}
44
45pub struct Declaration<'a>(pub &'a ForwardedField);
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 ForwardedField);
58
59impl ToTokens for ValuePopulator<'_> {
60    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
61        let ForwardedField { 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 MatchArms<'a>(&'a ForwardAttrs<'a>);
71
72impl ToTokens for MatchArms<'_> {
73    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
74        if !self.0.will_forward_any() {
75            tokens.append_all(quote!(_ => continue));
76            return;
77        }
78
79        let push_command = quote!(__fwd_attrs.push(__attr.clone()));
80
81        tokens.append_all(
82            match self
83                .0
84                .filter
85                .expect("Can only forward attributes if filter is defined")
86            {
87                ForwardAttrsFilter::All => quote!(_ => #push_command),
88                ForwardAttrsFilter::Only(idents) => {
89                    let names = idents.to_strings();
90                    quote! {
91                        #(#names)|* => #push_command,
92                        _ => continue,
93                    }
94                }
95            },
96        );
97    }
98}
darling_core/codegen/attrs_field.rs

darling_core/codegen/
attrs_field.rs
