servo_dom_struct/
domobject.rs

1/* This Source Code Form is subject to the terms of the Mozilla Public
2 * License, v. 2.0. If a copy of the MPL was not distributed with this
3 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
4
5use quote::{TokenStreamExt, quote};
6
7/// First field of DomObject must be either reflector or another dom_struct,
8/// all other fields must not implement DomObject
9pub(crate) fn expand_dom_object(
10    input: syn::ItemStruct,
11    associated_memory: bool,
12) -> proc_macro2::TokenStream {
13    let fields = input.fields.iter().collect::<Vec<&syn::Field>>();
14    let (first_field, fields) = fields
15        .split_first()
16        .expect("#[dom_struct] should not be applied on empty structs");
17
18    let first_field_name = first_field.ident.as_ref().unwrap();
19    let reflector_type = if associated_memory {
20        quote! { crate::AssociatedMemory }
21    } else {
22        quote! { () }
23    };
24    let mut field_types_and_cfgs = vec![];
25    for field in fields {
26        if field_types_and_cfgs.contains(&(&field.ty, vec![])) {
27            continue;
28        }
29        let cfgs = field
30            .attrs
31            .iter()
32            .filter(|a| a.path().is_ident("cfg"))
33            .collect::<Vec<_>>();
34        field_types_and_cfgs.push((&field.ty, cfgs));
35    }
36
37    let name = &input.ident;
38    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
39    let items = quote! {
40        impl #impl_generics ::js::conversions::ToJSValConvertible for #name #ty_generics #where_clause {
41            #[expect(unsafe_code)]
42            unsafe fn to_jsval(&self,
43                                cx: *mut js::jsapi::JSContext,
44                                rval: js::rust::MutableHandleValue) {
45                let object = crate::DomObject::reflector(self).get_jsobject();
46                object.to_jsval(cx, rval)
47            }
48        }
49
50        impl #impl_generics crate::DomObject for #name #ty_generics #where_clause {
51            type ReflectorType = #reflector_type;
52
53            #[inline]
54            fn reflector(&self) -> &crate::Reflector<Self::ReflectorType> {
55                self.#first_field_name.reflector()
56            }
57        }
58
59        impl #impl_generics crate::MutDomObject for #name #ty_generics #where_clause {
60            unsafe fn init_reflector<Actual>(&self, obj: *mut js::jsapi::JSObject) {
61                self.#first_field_name.init_reflector::<Actual>(obj);
62            }
63            unsafe fn init_reflector_without_associated_memory(&self, obj: *mut js::jsapi::JSObject) {
64                self.#first_field_name.init_reflector_without_associated_memory(obj);
65            }
66        }
67
68        impl #impl_generics Eq for #name #ty_generics #where_clause {}
69
70        impl #impl_generics PartialEq for #name #ty_generics #where_clause {
71            fn eq(&self, other: &Self) -> bool {
72                crate::DomObject::reflector(self) == crate::DomObject::reflector(other)
73            }
74        }
75    };
76
77    let mut params = proc_macro2::TokenStream::new();
78    params.append_separated(
79        input.generics.type_params().map(|param| &param.ident),
80        quote! {,},
81    );
82
83    let mut dummy_items = quote! {
84        // Generic trait with a blanket impl over `()` for all types.
85        // becomes ambiguous if impl
86        trait NoDomObjectInDomObject<A> {
87            // Required for actually being able to reference the trait.
88            fn some_item() {}
89        }
90
91        impl<T: ?Sized> NoDomObjectInDomObject<()> for T {}
92
93        // Used for the specialized impl when DomObject is implemented.
94        #[expect(dead_code)]
95        struct Invalid;
96        // forbids DomObject
97        impl<T> NoDomObjectInDomObject<Invalid> for T where T: ?Sized + crate::DomObject {}
98    };
99
100    dummy_items.append_all(
101        field_types_and_cfgs
102            .iter()
103            .enumerate()
104            .map(|(i, (ty, cfgs))| {
105                let s = syn::Ident::new(&format!("S{i}"), proc_macro2::Span::call_site());
106                quote! {
107                    struct #s<#params>(#params);
108
109                    impl #impl_generics #s<#params> #where_clause {
110                        #(#cfgs)*
111                        fn f() {
112                            // If there is only one specialized trait impl, type inference with
113                            // `_` can be resolved and this can compile. Fails to compile if
114                            // ty implements `NoDomObjectInDomObject<Invalid>`.
115                            let _ = <#ty as NoDomObjectInDomObject<_>>::some_item;
116                        }
117                    }
118                }
119            }),
120    );
121
122    let dummy_const = syn::Ident::new(
123        &format!("_IMPL_DOMOBJECT_FOR_{}", name),
124        proc_macro2::Span::call_site(),
125    );
126    let tokens = quote! {
127        #[expect(non_upper_case_globals)]
128        const #dummy_const: () = { #dummy_items };
129        #items
130    };
131
132    tokens
133}
servo_dom_struct/domobject.rs

servo_dom_struct/
domobject.rs
