1 | use proc_macro2::TokenStream; |
2 | use quote::{quote, ToTokens, TokenStreamExt}; |
3 | use syn::{GenericParam, Generics, Path, TraitBound, TraitBoundModifier, TypeParamBound}; |
4 | |
5 | use crate::codegen::TraitImpl; |
6 | use crate::usage::IdentSet; |
7 | |
8 | /// Wrapper for "outer From" traits, such as `FromDeriveInput`, `FromVariant`, and `FromField`. |
9 | pub 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 | impl #impl_generics #trayt for #ty_ident #ty_generics |
31 | #where_clause |
32 | { |
33 | #body |
34 | } |
35 | )); |
36 | } |
37 | } |
38 | |
39 | fn compute_impl_bounds(bound: Path, mut generics: Generics, applies_to: &IdentSet) -> Generics { |
40 | if generics.params.is_empty() { |
41 | return generics; |
42 | } |
43 | |
44 | let added_bound: TypeParamBound = TypeParamBound::Trait(TraitBound { |
45 | paren_token: None, |
46 | modifier: TraitBoundModifier::None, |
47 | lifetimes: None, |
48 | path: bound, |
49 | }); |
50 | |
51 | for param: &mut GenericParam in generics.params.iter_mut() { |
52 | if let GenericParam::Type(ref mut typ: &mut TypeParam) = *param { |
53 | if applies_to.contains(&typ.ident) { |
54 | typ.bounds.push(added_bound.clone()); |
55 | } |
56 | } |
57 | } |
58 | |
59 | generics |
60 | } |
61 | |