Move generated bindings to script_bindings (#36323)

This is the final step of #1799, where the majority of the generated
code for the JS bindings is now compiled as part of the script_bindings
build step. The remaining pieces in script must live there because they
refer to concrete DOM types; all code in script_bindings is generic over
the
[DomTypes](https://doc.servo.org/script/dom/bindings/codegen/DomTypes/trait.DomTypes.html)
trait.

My testing with incremental builds shows me a 12 second reduction in
build times on my 2024 M4 Macbook Pro when modifying code in the script
crate after these changes. Before this PR those changes took 20 seconds
to rebuild Servo, and now they take 8 seconds.

Testing: Existing WPT tests ensure no regressions.
Fixes: #1799

---------

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

1 files changed, 64 insertions, 0 deletions

diff --git a/components/script_bindings/realms.rs b/components/script_bindings/realms.rs
new file mode 100644
index 00000000000..3fe60d5ae5c
--- /dev/null
+++ b/components/script_bindings/realms.rs
@@ -0,0 +1,64 @@
+/* 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 js::jsapi::{GetCurrentRealmOrNull, JSAutoRealm};
+
+use crate::DomTypes;
+use crate::interfaces::GlobalScopeHelpers;
+use crate::reflector::DomObject;
+use crate::script_runtime::JSContext;
+
+pub struct AlreadyInRealm(());
+
+impl AlreadyInRealm {
+    #![allow(unsafe_code)]
+    pub fn assert<D: DomTypes>() -> AlreadyInRealm {
+        unsafe {
+            assert!(!GetCurrentRealmOrNull(*D::GlobalScope::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> From<&'a AlreadyInRealm> for InRealm<'a> {
+    fn from(token: &'a AlreadyInRealm) -> InRealm<'a> {
+        InRealm::already(token)
+    }
+}
+
+impl<'a> From<&'a JSAutoRealm> for InRealm<'a> {
+    fn from(token: &'a JSAutoRealm) -> InRealm<'a> {
+        InRealm::entered(token)
+    }
+}
+
+impl InRealm<'_> {
+    pub fn already(token: &AlreadyInRealm) -> InRealm {
+        InRealm::Already(token)
+    }
+
+    pub fn entered(token: &JSAutoRealm) -> InRealm {
+        InRealm::Entered(token)
+    }
+}
+
+pub fn enter_realm<D: DomTypes>(object: &impl DomObject) -> JSAutoRealm {
+    JSAutoRealm::new(
+        *D::GlobalScope::get_cx(),
+        object.reflector().get_jsobject().get(),
+    )
+}