libservo: Allow embedders to execute JavaScript scripts via the API (#35720)

This change adds a new `WebView` API `evaluate_javascript()`, which
allows embedders to
execute JavaScript code and wait for a reply asynchronously. Ongoing
script execution is
tracked by a libservo `JavaScriptEvaluator` struct, which maps an id to
the callback passed
to the `evaluate_javascript()` method. The id is used to track the
script and its execution
through the other parts of Servo.

Testing: This changes includes `WebView` unit tests.

---------

Signed-off-by: Narfinger <Narfinger@users.noreply.github.com>
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>

components/servo/tests/webview.rs

@@ -11,12 +11,14 @@
 
 mod common;
 
-use std::cell::Cell;
+use std::cell::{Cell, RefCell};
 use std::rc::Rc;
 
 use anyhow::ensure;
 use common::{ServoTest, run_api_tests};
-use servo::{WebViewBuilder, WebViewDelegate};
+use servo::{
+    JSValue, JavaScriptEvaluationError, LoadStatus, WebView, WebViewBuilder, WebViewDelegate,
+};
 
 #[derive(Default)]
 struct WebViewDelegateImpl {
@@ -44,6 +46,81 @@ fn test_create_webview(servo_test: &ServoTest) -> Result<(), anyhow::Error> {
     Ok(())
 }
 
+fn evaluate_javascript(
+    servo_test: &ServoTest,
+    webview: WebView,
+    script: impl ToString,
+) -> Result<JSValue, JavaScriptEvaluationError> {
+    let load_webview = webview.clone();
+    let _ = servo_test.spin(move || Ok(load_webview.load_status() != LoadStatus::Complete));
+
+    let saved_result = Rc::new(RefCell::new(None));
+    let callback_result = saved_result.clone();
+    webview.evaluate_javascript(script, move |result| {
+        *callback_result.borrow_mut() = Some(result)
+    });
+
+    let spin_result = saved_result.clone();
+    let _ = servo_test.spin(move || Ok(spin_result.borrow().is_none()));
+
+    (*saved_result.borrow())
+        .clone()
+        .expect("Should have waited until value available")
+}
+
+fn test_evaluate_javascript_basic(servo_test: &ServoTest) -> Result<(), anyhow::Error> {
+    let delegate = Rc::new(WebViewDelegateImpl::default());
+    let webview = WebViewBuilder::new(servo_test.servo())
+        .delegate(delegate.clone())
+        .build();
+
+    let result = evaluate_javascript(servo_test, webview.clone(), "undefined");
+    ensure!(result == Ok(JSValue::Undefined));
+
+    let result = evaluate_javascript(servo_test, webview.clone(), "null");
+    ensure!(result == Ok(JSValue::Null));
+
+    let result = evaluate_javascript(servo_test, webview.clone(), "42");
+    ensure!(result == Ok(JSValue::Number(42.0)));
+
+    let result = evaluate_javascript(servo_test, webview.clone(), "3 + 4");
+    ensure!(result == Ok(JSValue::Number(7.0)));
+
+    let result = evaluate_javascript(servo_test, webview.clone(), "'abc' + 'def'");
+    ensure!(result == Ok(JSValue::String("abcdef".into())));
+
+    let result = evaluate_javascript(servo_test, webview.clone(), "let foo = {blah: 123}; foo");
+    ensure!(matches!(result, Ok(JSValue::Object(_))));
+    if let Ok(JSValue::Object(values)) = result {
+        ensure!(values.len() == 1);
+        ensure!(values.get("blah") == Some(&JSValue::Number(123.0)));
+    }
+
+    let result = evaluate_javascript(servo_test, webview.clone(), "[1, 2, 3, 4]");
+    let expected = JSValue::Array(vec![
+        JSValue::Number(1.0),
+        JSValue::Number(2.0),
+        JSValue::Number(3.0),
+        JSValue::Number(4.0),
+    ]);
+    ensure!(result == Ok(expected));
+
+    let result = evaluate_javascript(servo_test, webview.clone(), "window");
+    ensure!(matches!(result, Ok(JSValue::Window(..))));
+
+    let result = evaluate_javascript(servo_test, webview.clone(), "document.body");
+    ensure!(matches!(result, Ok(JSValue::Element(..))));
+
+    let result = evaluate_javascript(
+        servo_test,
+        webview.clone(),
+        "document.body.innerHTML += '<iframe>'; frames[0]",
+    );
+    ensure!(matches!(result, Ok(JSValue::Frame(..))));
+
+    Ok(())
+}
+
 fn test_create_webview_and_immediately_drop_webview_before_shutdown(
     servo_test: &ServoTest,
 ) -> Result<(), anyhow::Error> {
@@ -54,6 +131,7 @@ fn test_create_webview_and_immediately_drop_webview_before_shutdown(
 fn main() {
     run_api_tests!(
         test_create_webview,
+        test_evaluate_javascript_basic,
         // This test needs to be last, as it tests creating and dropping
         // a WebView right before shutdown.
         test_create_webview_and_immediately_drop_webview_before_shutdown