Implement WebDriver FindElementFromElement command

components/script/script_thread.rs

@@ -1807,6 +1807,15 @@ impl ScriptThread {
                     reply,
                 )
             },
+            WebDriverScriptCommand::FindElementElementCSS(selector, element_id, reply) => {
+                webdriver_handlers::handle_find_element_element_css(
+                    &*documents,
+                    pipeline_id,
+                    element_id,
+                    selector,
+                    reply,
+                )
+            },
             WebDriverScriptCommand::FocusElement(element_id, reply) => {
                 webdriver_handlers::handle_focus_element(
                     &*documents,

components/script/webdriver_handlers.rs

@@ -203,6 +203,23 @@ pub fn handle_find_elements_css(
     reply.send(node_ids).unwrap();
 }
 
+pub fn handle_find_element_element_css(
+    documents: &Documents,
+    pipeline: PipelineId,
+    element_id: String,
+    selector: String,
+    reply: IpcSender<Result<Option<String>, ()>>,
+) {
+    let node_id = find_node_by_unique_id(documents, pipeline, element_id)
+        .ok_or(())
+        .and_then(|node| {
+            node.query_selector(DOMString::from(selector))
+                .map_err(|_| ())
+        })
+        .map(|node| node.map(|x| x.upcast::<Node>().unique_id()));
+    reply.send(node_id).unwrap();
+}
+
 pub fn handle_focus_element(
     documents: &Documents,
     pipeline: PipelineId,

components/script_traits/webdriver_msg.rs

@@ -25,6 +25,7 @@ pub enum WebDriverScriptCommand {
     ExecuteAsyncScript(String, IpcSender<WebDriverJSResult>),
     FindElementCSS(String, IpcSender<Result<Option<String>, ()>>),
     FindElementsCSS(String, IpcSender<Result<Vec<String>, ()>>),
+    FindElementElementCSS(String, String, IpcSender<Result<Option<String>, ()>>),
     FocusElement(String, IpcSender<Result<(), ()>>),
     GetActiveElement(IpcSender<Option<String>>),
     GetCookie(String, IpcSender<Vec<Serde<Cookie<'static>>>>),

components/webdriver_server/lib.rs

@@ -766,6 +766,42 @@ impl Handler {
         }
     }
 
+    // https://w3c.github.io/webdriver/#find-element-from-element
+    fn handle_find_element_element(
+        &self,
+        element: &WebElement,
+        parameters: &LocatorParameters,
+    ) -> WebDriverResult<WebDriverResponse> {
+        if parameters.using != LocatorStrategy::CSSSelector {
+            return Err(WebDriverError::new(
+                ErrorStatus::UnsupportedOperation,
+                "Unsupported locator strategy",
+            ));
+        }
+
+        let (sender, receiver) = ipc::channel().unwrap();
+        let cmd = WebDriverScriptCommand::FindElementElementCSS(
+            parameters.value.clone(),
+            element.id.clone(),
+            sender,
+        );
+
+        self.browsing_context_script_command(cmd)?;
+
+        match receiver.recv().unwrap() {
+            Ok(value) => {
+                let value_resp = serde_json::to_value(
+                    value.map(|x| serde_json::to_value(WebElement::new(x)).unwrap()),
+                )?;
+                Ok(WebDriverResponse::Generic(ValueResponse(value_resp)))
+            },
+            Err(_) => Err(WebDriverError::new(
+                ErrorStatus::InvalidSelector,
+                "Invalid selector",
+            )),
+        }
+    }
+
     // https://w3c.github.io/webdriver/webdriver-spec.html#get-element-rect
     fn handle_element_rect(&self, element: &WebElement) -> WebDriverResult<WebDriverResponse> {
         let (sender, receiver) = ipc::channel().unwrap();
@@ -1192,6 +1228,9 @@ impl WebDriverHandler<ServoExtensionRoute> for Handler {
             WebDriverCommand::SwitchToParentFrame => self.handle_switch_to_parent_frame(),
             WebDriverCommand::FindElement(ref parameters) => self.handle_find_element(parameters),
             WebDriverCommand::FindElements(ref parameters) => self.handle_find_elements(parameters),
+            WebDriverCommand::FindElementElement(ref element, ref parameters) => {
+                self.handle_find_element_element(element, parameters)
+            },
             WebDriverCommand::GetNamedCookie(ref name) => self.handle_get_cookie(name),
             WebDriverCommand::GetCookies => self.handle_get_cookies(),
             WebDriverCommand::GetActiveElement => self.handle_active_element(),