1 files changed, 50 insertions, 0 deletions
diff --git a/components/script/realms.rs b/components/script/realms.rs
new file mode 100644
index 00000000000..280e615e412
--- /dev/null
+++ b/components/script/realms.rs
@@ -0,0 +1,50 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use crate::dom::bindings::reflector::DomObject;
+use crate::dom::globalscope::GlobalScope;
+use crate::script_runtime::JSContext;
+use js::jsapi::{GetCurrentRealmOrNull, JSAutoRealm};
+
+pub struct AlreadyInRealm(());
+
+impl AlreadyInRealm {
+    #![allow(unsafe_code)]
+    pub fn assert(global: &GlobalScope) -> AlreadyInRealm {
+        unsafe {
+            assert!(!GetCurrentRealmOrNull(*global.get_cx()).is_null());
+        }
+        AlreadyInRealm(())
+    }
+
+    pub fn assert_for_cx(cx: JSContext) -> AlreadyInRealm {
+        unsafe {
+            assert!(!GetCurrentRealmOrNull(*cx).is_null());
+        }
+        AlreadyInRealm(())
+    }
+}
+
+#[derive(Clone, Copy)]
+pub enum InRealm<'a> {
+    Already(&'a AlreadyInRealm),
+    Entered(&'a JSAutoRealm),
+}
+
+impl<'a> InRealm<'a> {
+    pub fn in_realm(token: &AlreadyInRealm) -> InRealm {
+        InRealm::Already(token)
+    }
+
+    pub fn entered(token: &JSAutoRealm) -> InRealm {
+        InRealm::Entered(token)
+    }
+}
+
+pub fn enter_realm(object: &impl DomObject) -> JSAutoRealm {
+    JSAutoRealm::new(
+        *object.global().get_cx(),
+        object.reflector().get_jsobject().get(),
+    )
+}