darling_core/codegen/
outer_from_impl.rs

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1use proc_macro2::TokenStream;
2use quote::{quote, ToTokens, TokenStreamExt};
3use syn::{GenericParam, Generics, Path, TraitBound, TraitBoundModifier, TypeParamBound};
4
5use crate::codegen::TraitImpl;
6use crate::usage::IdentSet;
7
8/// Wrapper for "outer From" traits, such as `FromDeriveInput`, `FromVariant`, and `FromField`.
9pub trait OuterFromImpl<'a> {
10    /// Gets the path of the trait being implemented.
11    fn trait_path(&self) -> Path;
12
13    fn base(&'a self) -> &'a TraitImpl<'a>;
14
15    fn trait_bound(&self) -> Path {
16        self.trait_path()
17    }
18
19    fn wrap<T: ToTokens>(&'a self, body: T, tokens: &mut TokenStream) {
20        let base = self.base();
21        let trayt = self.trait_path();
22        let ty_ident = base.ident;
23        // The type parameters used in non-skipped, non-magic fields.
24        // These must impl `FromMeta` unless they have custom bounds.
25        let used = base.used_type_params();
26        let generics = compute_impl_bounds(self.trait_bound(), base.generics.clone(), &used);
27        let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
28
29        tokens.append_all(quote!(
30            #[automatically_derived]
31            #[allow(clippy::manual_unwrap_or_default)]
32            impl #impl_generics #trayt for #ty_ident #ty_generics
33                #where_clause
34            {
35                #body
36            }
37        ));
38    }
39}
40
41fn compute_impl_bounds(bound: Path, mut generics: Generics, applies_to: &IdentSet) -> Generics {
42    if generics.params.is_empty() {
43        return generics;
44    }
45
46    let added_bound = TypeParamBound::Trait(TraitBound {
47        paren_token: None,
48        modifier: TraitBoundModifier::None,
49        lifetimes: None,
50        path: bound,
51    });
52
53    for param in generics.params.iter_mut() {
54        if let GenericParam::Type(ref mut typ) = *param {
55            if applies_to.contains(&typ.ident) {
56                typ.bounds.push(added_bound.clone());
57            }
58        }
59    }
60
61    generics
62}
darling_core/codegen/outer_from_impl.rs

darling_core/codegen/
outer_from_impl.rs
