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Replace ShouldNotImplDomObject with NoDomObjectInDomObject (#33627)

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This is https://github.com/jdm/servo/pull/1 rebased on servo/servo

Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>
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Samson 2024-10-03 14:58:34 +02:00 • committed by GitHub
parent cd803c8341
commit 634dbd2d78
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1 changed files with 33 additions and 20 deletions
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53
components/domobject_derive/lib.rs
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@ -5,8 +5,9 @@
#![recursion_limit = "128"]
use quote::{quote, TokenStreamExt};
use syn::parse_quote;
/// First field of DomObject must be either reflector or another dom_struct,
/// all other fields must not implement DomObject
#[proc_macro_derive(DomObject)]
pub fn expand_token_stream(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let input = syn::parse(input).unwrap();
@ -65,33 +66,45 @@ fn expand_dom_object(input: syn::DeriveInput) -> proc_macro2::TokenStream {
crate::DomObject::reflector(self) == crate::DomObject::reflector(other)
}
}
// Generic trait with a blanket impl over `()` for all types.
// becomes ambiguous if impl
trait NoDomObjectInDomObject<A> {
// Required for actually being able to reference the trait.
fn some_item() {}
}
impl<T: ?Sized> NoDomObjectInDomObject<()> for T {}
// Used for the specialized impl when DomObject is implemented.
#[allow(dead_code)]
struct Invalid;
// forbids DomObject
impl<T> NoDomObjectInDomObject<Invalid> for T where T: ?Sized + crate::DomObject {}
};
let mut params = proc_macro2::TokenStream::new();
params.append_separated(input.generics.type_params().map(|param| &param.ident), ", ");
params.append_separated(
input.generics.type_params().map(|param| &param.ident),
quote! {,},
);
// For each field in the struct, we implement ShouldNotImplDomObject for a
// pair of all the type parameters of the DomObject and and the field type.
// This allows us to support parameterized DOM objects
// such as IteratorIterable<T>.
items.append_all(field_types.iter().map(|ty| {
items.append_all(field_types.iter().enumerate().map(|(i, ty)| {
let s = syn::Ident::new(&format!("S{i}"), proc_macro2::Span::call_site());
quote! {
impl #impl_generics ShouldNotImplDomObject for ((#params), #ty) #where_clause {}
struct #s<#params>(#params);
impl #impl_generics #s<#params> #where_clause {
fn f() {
// If there is only one specialized trait impl, type inference with
// `_` can be resolved and this can compile. Fails to compile if
// ty implements `NoDomObjectInDomObject<Invalid>`.
let _ = <#ty as NoDomObjectInDomObject<_>>::some_item;
}
}
}
}));
let mut generics = input.generics.clone();
generics.params.push(parse_quote!(
__T: crate::DomObject
));
let (impl_generics, _, where_clause) = generics.split_for_impl();
items.append_all(quote! {
trait ShouldNotImplDomObject {}
impl #impl_generics ShouldNotImplDomObject for ((#params), __T) #where_clause {}
});
let dummy_const = syn::Ident::new(
&format!("_IMPL_DOMOBJECT_FOR_{}", name),
proc_macro2::Span::call_site(),