Implement ElementInternals::shadowRoot (#35923)

* Implement ElementInternals::shadowRoot

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

* Update WPT expectations

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

---------

Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>

components/script/dom/element.rs

@@ -542,6 +542,16 @@ impl Element {
             clonable,
             can_gc,
         );
+
+        // Step 7. If element’s custom element state is "precustomized" or "custom",
+        // then set shadow’s available to element internals to true.
+        if matches!(
+            self.get_custom_element_state(),
+            CustomElementState::Precustomized | CustomElementState::Custom
+        ) {
+            shadow_root.set_available_to_element_internals(true);
+        }
+
         self.ensure_rare_data().shadow_root = Some(Dom::from_ref(&*shadow_root));
         shadow_root
             .upcast::<Node>()

components/script/dom/elementinternals.rs

@@ -23,6 +23,7 @@ use crate::dom::htmlelement::HTMLElement;
 use crate::dom::htmlformelement::{FormDatum, FormDatumValue, HTMLFormElement};
 use crate::dom::node::{Node, NodeTraits};
 use crate::dom::nodelist::NodeList;
+use crate::dom::shadowroot::ShadowRoot;
 use crate::dom::validation::{Validatable, is_barred_by_datalist_ancestor};
 use crate::dom::validitystate::{ValidationFlags, ValidityState};
 use crate::script_runtime::CanGc;
@@ -188,6 +189,22 @@ impl ElementInternals {
 }
 
 impl ElementInternalsMethods<crate::DomTypeHolder> for ElementInternals {
+    /// <https://html.spec.whatwg.org/multipage/#dom-elementinternals-shadowroot>
+    fn GetShadowRoot(&self) -> Option<DomRoot<ShadowRoot>> {
+        // Step 1. Let target be this's target element.
+        // Step 2. If target is not a shadow host, then return null.
+        // Step 3. Let shadow be target's shadow root.
+        let shadow = self.target_element.upcast::<Element>().shadow_root()?;
+
+        // Step 4. If shadow's available to element internals is false, then return null.
+        if !shadow.is_available_to_element_internals() {
+            return None;
+        }
+
+        // Step 5. Return shadow.
+        Some(shadow)
+    }
+
     /// <https://html.spec.whatwg.org/multipage#dom-elementinternals-setformvalue>
     fn SetFormValue(
         &self,

components/script/dom/shadowroot.rs

@@ -2,6 +2,7 @@
  * 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 std::cell::Cell;
 use std::collections::HashMap;
 use std::collections::hash_map::Entry;
 
@@ -72,6 +73,9 @@ pub(crate) struct ShadowRoot {
     /// <https://dom.spec.whatwg.org/#dom-shadowroot-clonable>
     clonable: bool,
 
+    /// <https://dom.spec.whatwg.org/#shadowroot-available-to-element-internals>
+    available_to_element_internals: Cell<bool>,
+
     slots: DomRefCell<HashMap<DOMString, Vec<Dom<HTMLSlotElement>>>>,
 }
 
@@ -103,6 +107,7 @@ impl ShadowRoot {
             mode,
             slot_assignment_mode,
             clonable,
+            available_to_element_internals: Cell::new(false),
             slots: Default::default(),
         }
     }
@@ -252,6 +257,15 @@ impl ShadowRoot {
     pub(crate) fn has_slot_descendants(&self) -> bool {
         !self.slots.borrow().is_empty()
     }
+
+    pub(crate) fn set_available_to_element_internals(&self, value: bool) {
+        self.available_to_element_internals.set(value);
+    }
+
+    /// <https://dom.spec.whatwg.org/#shadowroot-available-to-element-internals>
+    pub(crate) fn is_available_to_element_internals(&self) -> bool {
+        self.available_to_element_internals.get()
+    }
 }
 
 impl ShadowRootMethods<crate::DomTypeHolder> for ShadowRoot {

components/script_bindings/webidls/ElementInternals.webidl

@@ -5,6 +5,9 @@
 // https://html.spec.whatwg.org/multipage/#elementinternals
 [Exposed=Window]
 interface ElementInternals {
+  // Shadow root access
+  readonly attribute ShadowRoot? shadowRoot;
+
   // Form-associated custom elements
 
   [Throws] undefined setFormValue((File or USVString or FormData)? value,

tests/wpt/meta/custom-elements/element-internals-shadowroot.html.ini

@@ -1,10 +1,4 @@
 [element-internals-shadowroot.html]
   expected: ERROR
-  [ElementInternals.shadowRoot allows access to open shadow root]
-    expected: FAIL
-
-  [ElementInternals.shadowRoot allows access to closed shadow root]
-    expected: FAIL
-
   [ElementInternals.shadowRoot doesn't reveal pre-attached closed shadowRoot]
     expected: FAIL

tests/wpt/meta/custom-elements/form-associated/ElementInternals-target-element-is-held-strongly.html.ini

@@ -1,3 +0,0 @@
-[ElementInternals-target-element-is-held-strongly.html]
-  [Target element of ElementsInternals is held strongly and doesn't get GCed if there are no other references]
-    expected: FAIL

tests/wpt/meta/html/dom/idlharness.https.html.ini

@@ -4940,9 +4940,6 @@
   [OffscreenCanvasRenderingContext2D interface: operation roundRect(unrestricted double, unrestricted double, unrestricted double, unrestricted double, optional (unrestricted double or DOMPointInit or sequence<(unrestricted double or DOMPointInit)>))]
     expected: FAIL
 
-  [ElementInternals interface: attribute shadowRoot]
-    expected: FAIL
-
   [ElementInternals interface: attribute states]
     expected: FAIL