script::webdriver_handler: Fully implement get_known_element (#37532)

1. `get_known_element`: Refactor to follow same step of spec (which
reduces unnecessary search) and implement previously missing step 4.2:
If node is stale return error with error code stale element reference.
An element is stale if its node document is not the active document or
if it is not connected.

2. Refactor `find_node_by_unique_id_in_document` to make it not check
error and really return a `Option<DomRoot<Node>>` as the name suggests.
This will greatly reduce duplication when implement [get a known shadow
root](https://w3c.github.io/webdriver/#dfn-get-a-known-shadow-root) soon

Testing: All WebDriver Conformance test after removing two problematic
commits in #37520

Signed-off-by: Euclid Ye <yezhizhenjiakang@gmail.com>

components/script/dom/window.rs

@@ -1439,14 +1439,11 @@ impl WindowMethods<crate::DomTypeHolder> for Window {
     }
 
     fn WebdriverElement(&self, id: DOMString) -> Option<DomRoot<Element>> {
-        find_node_by_unique_id_in_document(&self.Document(), id.into())
+        find_node_by_unique_id_in_document(&self.Document(), id.into()).and_then(Root::downcast)
-            .ok()
-            .and_then(Root::downcast)
     }
 
     fn WebdriverFrame(&self, id: DOMString) -> Option<DomRoot<Element>> {
         find_node_by_unique_id_in_document(&self.Document(), id.into())
-            .ok()
             .and_then(Root::downcast::<HTMLIFrameElement>)
             .map(Root::upcast::<Element>)
     }
@@ -1457,9 +1454,7 @@ impl WindowMethods<crate::DomTypeHolder> for Window {
     }
 
     fn WebdriverShadowRoot(&self, id: DOMString) -> Option<DomRoot<ShadowRoot>> {
-        find_node_by_unique_id_in_document(&self.Document(), id.into())
+        find_node_by_unique_id_in_document(&self.Document(), id.into()).and_then(Root::downcast)
-            .ok()
-            .and_then(Root::downcast)
     }
 
     // https://drafts.csswg.org/cssom/#dom-window-getcomputedstyle

components/script/webdriver_handlers.rs

@@ -80,35 +80,48 @@ fn get_known_element(
     let doc = documents
         .find_document(pipeline)
         .expect("webdriver_handlers::Document should exists");
+    // Step 1. If not node reference is known with session, session's current browsing context,
+    // and reference return error with error code no such element.
+    if !ScriptThread::has_node_id(pipeline, &node_id) {
+        // If the node is known, but not found in the document, it is stale.
+        return Err(ErrorStatus::NoSuchElement);
+    }
+    // Step 2.Let node be the result of get a node with session,
+    // session's current browsing context, and reference.
+    let node = find_node_by_unique_id_in_document(&doc, node_id);
+
     // Step 3. If node is not null and node does not implement Element
     // return error with error code no such element.
-    find_node_by_unique_id_in_document(&doc, node_id).and_then(|node| {
+    if let Some(ref node) = node {
-        node.downcast::<Element>()
+        if !node.is::<Element>() {
-            .map(DomRoot::from_ref)
+            return Err(ErrorStatus::NoSuchElement);
-            .ok_or(ErrorStatus::NoSuchElement)
+        }
-    })
+    }
+    // Step 4.1. If node is null return error with error code stale element reference.
+    if node.is_none() {
+        return Err(ErrorStatus::StaleElementReference);
+    }
+    // Step 4.2. If node is stale return error with error code stale element reference.
+    // An element is stale if its node document is not the active document
+    // or if it is not connected.
+    let element = DomRoot::from_ref(node.unwrap().downcast::<Element>().unwrap());
+    if !element.owner_document().is_active() || !element.is_connected() {
+        return Err(ErrorStatus::StaleElementReference);
+    }
+    // Step 5. Return success with data node.
+    Ok(element)
 }
 
 // This is also used by `dom/window.rs`
 pub(crate) fn find_node_by_unique_id_in_document(
     document: &Document,
     node_id: String,
-) -> Result<DomRoot<Node>, ErrorStatus> {
+) -> Option<DomRoot<Node>> {
     let pipeline = document.window().pipeline_id();
-    match document
+    document
         .upcast::<Node>()
         .traverse_preorder(ShadowIncluding::Yes)
         .find(|node| node.unique_id(pipeline) == node_id)
-    {
-        Some(node) => Ok(node),
-        None => {
-            if ScriptThread::has_node_id(pipeline, &node_id) {
-                Err(ErrorStatus::StaleElementReference)
-            } else {
-                Err(ErrorStatus::NoSuchElement)
-            }
-        },
-    }
 }
 
 /// <https://w3c.github.io/webdriver/#dfn-link-text-selector>