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script: Return global objects for DOM objects in the relevant realm (#37120)

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DomObject::global is a tricky API because it's used pervasively but has
subtle requirements that are not documented and not yet enforced by the
type system (#36116). The method returns the relevant global object for
a given DOM object, but that operation is only meaningful if there is an
active realm. We usually, but not always, have an active realm.

This change avoids a footgun by following the principle of least
surprise. Rather than making every single caller of `something.global()`
both prove that there is an active realm and think about which realm
they want active, we implement the obvious behaviour: always activate
the realm of the callee before obtaining the relevant global.
 
Testing: Existing WPT coverage is sufficient; this method is called all
over the codebase.
Fixes: #37070 #27037

Signed-off-by: Josh Matthews <josh@joshmatthews.net>
This commit is contained in:
Josh Matthews 2025-05-24 23:21:05 -04:00 • committed by GitHub
parent 0d44ca8ddc
commit 3a04f4195e
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2 changed files with 13 additions and 14 deletions
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14
components/script/dom/bindings/reflector.rs
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@ -11,7 +11,7 @@ use crate::DomTypes;
use crate::dom::bindings::conversions::DerivedFrom;
use crate::dom::bindings::root::DomRoot;
use crate::dom::globalscope::GlobalScope;
use crate::realms::InRealm;
use crate::realms::{InRealm, enter_realm};
use crate::script_runtime::CanGc;
/// Create the reflector for a new DOM object and yield ownership to the
@ -42,7 +42,16 @@ where
}
pub(crate) trait DomGlobal {
/// Returns the [relevant global] in whatever realm is currently active.
///
/// [relevant global]: https://html.spec.whatwg.org/multipage/#concept-relevant-global
fn global_(&self, realm: InRealm) -> DomRoot<GlobalScope>;
/// Returns the [relevant global] in the same realm as the callee object.
/// If you know the callee's realm is already the current realm, it is
/// more efficient to call [DomGlobal::global_] instead.
///
/// [relevant global]: https://html.spec.whatwg.org/multipage/#concept-relevant-global
fn global(&self) -> DomRoot<GlobalScope>;
}
@ -51,7 +60,8 @@ impl<T: DomGlobalGeneric<crate::DomTypeHolder>> DomGlobal for T {
<Self as DomGlobalGeneric<crate::DomTypeHolder>>::global_(self, realm)
}
fn global(&self) -> DomRoot<GlobalScope> {
<Self as DomGlobalGeneric<crate::DomTypeHolder>>::global(self)
let realm = enter_realm(self);
<Self as DomGlobalGeneric<crate::DomTypeHolder>>::global_(self, InRealm::entered(&realm))
}
}