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

domobject_derive/
lib.rs
