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No tracing of nop traceable fields (#29926)
* Add `no_trace` option to JSTraceable derive * NoTrace wrapper * Port some types to no_trace schematics * Fixing my unsafe mistakes (not tracing traceables) * Add docs & safety guards for no_trace Safety guards (trait shenanigans) guarantees safety usage of `no_trace` * Port canvas_traits to no_trace * Port servo_media to no_trace * Port net_traits to no_trace * Port style to no_trace * Port webgpu to no_trace * Port script_traits to no_trace * Port canvas_traits, devtools_traits, embedder_traits, profile_traits to no_trace * unrooted_must_root lint in seperate file * Add trace_in_no_trace_lint as script_plugin * Composable types in must_not_have_traceable * Introduced HashMapTracedValues wrapper * `HashMap<NoTrace<K>,V>`->`HashMapTracedValues<K,V>` * Port rest of servo's types to no_trace * Port html5ever, euclid, mime and http to no_trace * Port remaining externals to no_trace * Port webxr and Arc<Mutex<_>> * Fix spelling in notrace doc
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167 changed files with 1903 additions and 1020 deletions
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@ -7,10 +7,160 @@ extern crate syn;
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#[macro_use]
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extern crate synstructure;
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decl_derive!([JSTraceable] => js_traceable_derive);
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decl_derive!([JSTraceable, attributes(no_trace)] =>
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/// Implements `JSTraceable` on structs and enums
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///
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/// Example:
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/// ```rust
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/// #[derive(JSTraceable)]
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/// struct S {
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/// js_managed: JSManagedType,
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/// #[no_trace]
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/// non_js: NonJSManagedType,
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/// }
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/// ```
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///
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/// creates:
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///
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/// ```rust
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/// unsafe impl JSTraceable for S {
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/// #[inline]
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/// unsafe fn trace(&self, tracer: *mut js::jsapi::JSTracer) {
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/// match *self {
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/// S {
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/// js_managed: ref __binding_0,
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/// non_js: ref __binding_1,
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/// } => {
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/// {
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/// __binding_0.trace(tracer);
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/// }
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/// {
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/// // __binding_1 is not traceable so we do not need to trace it
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/// }
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/// },
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/// }
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/// }
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/// }
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/// ```
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///
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/// In cases where there is a need to make type (empty) traceable (`HashMap<NoTraceable, Traceable>`),
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/// NoTrace wrapper can be used, because it implements empty traceble:
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/// ```rust
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/// unsafe impl<T> JSTraceable for NoTrace<T> {
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/// unsafe fn trace(&self, _: *mut ::js::jsapi::JSTracer) { /* nop */}
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/// }
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/// ```
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///
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/// ## SAFETY
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/// Puting `#[no_trace]` on fields is safe if there are no types that are JS managed in that field.
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/// `#[no_trace]` should NOT be put on field that does implement (non-empty) `JSTraceable` (is JS managed).
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/// There are safeguards in place to prevent such mistakes. Example error:
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///
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/// ```console
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/// error[E0282]: type annotations needed
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/// |
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/// | #[derive(JSTraceable, MallocSizeOf)]
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/// | ^^^^^^^^^^^ cannot infer type of the type parameter `Self` declared on the trait `NoTraceOnJSTraceable`
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/// |
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/// = note: this error originates in the derive macro `JSTraceable`
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/// ```
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///
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/// If you can assure that type has empty JSTraceable impl, you can bypass guards, providing your reasoning:
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/// ```rust
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/// #[derive(JSTraceable)]
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/// struct S {
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/// #[no_trace = "Safe because both u32 and u64 are empty traceable"]
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/// field: HashMap<u32, u64>,
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/// }
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/// ```
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js_traceable_derive);
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// based off https://docs.rs/static_assertions/latest/src/static_assertions/assert_impl.rs.html#263
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fn assert_not_impl_traceable(ty: &syn::Type) -> proc_macro2::TokenStream {
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quote!(
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const _: fn() = || {
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// Generic trait with a blanket impl over `()` for all types.
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// becomes ambiguous if impl
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trait NoTraceOnJSTraceable<A> {
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// Required for actually being able to reference the trait.
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fn some_item() {}
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}
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impl<T: ?Sized> NoTraceOnJSTraceable<()> for T {}
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// Used for the specialized impl when JSTraceable is implemented.
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#[allow(dead_code)]
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struct Invalid0;
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// forbids JSTraceable
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impl<T> NoTraceOnJSTraceable<Invalid0> for T where T: ?Sized + crate::dom::bindings::trace::JSTraceable {}
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#[allow(dead_code)]
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struct Invalid2;
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// forbids HashMap<JSTraceble, _>
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impl<K, V, S> NoTraceOnJSTraceable<Invalid2> for std::collections::HashMap<K, V, S>
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where
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K: crate::dom::bindings::trace::JSTraceable + std::cmp::Eq + std::hash::Hash,
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S: std::hash::BuildHasher,
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{
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}
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#[allow(dead_code)]
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struct Invalid3;
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// forbids HashMap<_, JSTraceble>
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impl<K, V, S> NoTraceOnJSTraceable<Invalid3> for std::collections::HashMap<K, V, S>
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where
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K: std::cmp::Eq + std::hash::Hash,
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V: crate::dom::bindings::trace::JSTraceable,
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S: std::hash::BuildHasher,
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{
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}
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#[allow(dead_code)]
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struct Invalid4;
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// forbids BTreeMap<_, JSTraceble>
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impl<K, V> NoTraceOnJSTraceable<Invalid4> for std::collections::BTreeMap<K, V> where
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K: crate::dom::bindings::trace::JSTraceable + std::cmp::Eq + std::hash::Hash
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{
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}
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#[allow(dead_code)]
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struct Invalid5;
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// forbids BTreeMap<_, JSTraceble>
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impl<K, V> NoTraceOnJSTraceable<Invalid5> for std::collections::BTreeMap<K, V>
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where
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K: std::cmp::Eq + std::hash::Hash,
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V: crate::dom::bindings::trace::JSTraceable,
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{
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}
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// If there is only one specialized trait impl, type inference with
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// `_` can be resolved and this can compile. Fails to compile if
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// ty implements `NoTraceOnJSTraceable<InvalidX>`.
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let _ = <#ty as NoTraceOnJSTraceable<_>>::some_item;
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};
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)
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}
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fn js_traceable_derive(s: synstructure::Structure) -> proc_macro2::TokenStream {
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let match_body = s.each(|binding| Some(quote!(#binding.trace(tracer);)));
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let mut asserts = quote!();
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let match_body = s.each(|binding| {
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for attr in binding.ast().attrs.iter() {
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match attr.parse_meta().unwrap() {
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syn::Meta::Path(ref path) | syn::Meta::List(syn::MetaList { ref path, .. }) => {
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if path.is_ident("no_trace") {
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asserts.extend(assert_not_impl_traceable(&binding.ast().ty));
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return None;
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}
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},
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syn::Meta::NameValue(syn::MetaNameValue { ref path, .. }) => {
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if path.is_ident("no_trace") {
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return None;
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}
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},
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}
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}
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Some(quote!(#binding.trace(tracer);))
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});
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let ast = s.ast();
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let name = &ast.ident;
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@ -24,6 +174,8 @@ fn js_traceable_derive(s: synstructure::Structure) -> proc_macro2::TokenStream {
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}
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let tokens = quote! {
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#asserts
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#[allow(unsafe_code)]
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unsafe impl #impl_generics crate::dom::bindings::trace::JSTraceable for #name #ty_generics #where_clause {
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#[inline]
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