Auto merge of #23171 - hundredeir:find_elem_elems, r=jdm

add webdriver command "Find elements from Element"

---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because ___

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components/webdriver_server/lib.rs

@@ -803,6 +803,44 @@ impl Handler {
         }
     }
 
+    // https://w3c.github.io/webdriver/#find-elements-from-element
+    fn handle_find_elements_from_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::FindElementElementsCSS(
+            parameters.value.clone(),
+            element.id.clone(),
+            sender,
+        );
+
+        self.browsing_context_script_command(cmd)?;
+
+        match receiver.recv().unwrap() {
+            Ok(value) => {
+                let value_resp = value
+                    .into_iter()
+                    .map(|x| serde_json::to_value(WebElement::new(x)).unwrap())
+                    .collect::<Vec<Value>>();
+                let value_resp = serde_json::Value::Array(value_resp);
+                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();
@@ -1273,6 +1311,9 @@ impl WebDriverHandler<ServoExtensionRoute> for Handler {
             WebDriverCommand::FindElementElement(ref element, ref parameters) => {
                 self.handle_find_element_element(element, parameters)
             },
+            WebDriverCommand::FindElementElements(ref element, ref parameters) => {
+                self.handle_find_elements_from_element(element, parameters)
+            },
             WebDriverCommand::GetNamedCookie(ref name) => self.handle_get_cookie(name),
             WebDriverCommand::GetCookies => self.handle_get_cookies(),
             WebDriverCommand::GetActiveElement => self.handle_active_element(),
@@ -1303,7 +1344,7 @@ impl WebDriverHandler<ServoExtensionRoute> for Handler {
             },
             _ => Err(WebDriverError::new(
                 ErrorStatus::UnsupportedOperation,
-                "Command not implemented",
+                format!("Command not implemented: {:?}", msg.command),
             )),
         }
     }