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>

2 files changed, 12 insertions, 4 deletions

diff --git a/components/shared/constellation/from_script_message.rs b/components/shared/constellation/from_script_message.rs
index 21665c24e57..3856def660e 100644
--- a/components/shared/constellation/from_script_message.rs
+++ b/components/shared/constellation/from_script_message.rs
@@ -15,8 +15,8 @@ use base::id::{
 use canvas_traits::canvas::{CanvasId, CanvasMsg};
 use devtools_traits::{DevtoolScriptControlMsg, ScriptToDevtoolsControlMsg, WorkerId};
 use embedder_traits::{
-    AnimationState, EmbedderMsg, FocusSequenceNumber, MediaSessionEvent, TouchEventResult,
-    ViewportDetails,
+    AnimationState, EmbedderMsg, FocusSequenceNumber, JSValue, JavaScriptEvaluationError,
+    JavaScriptEvaluationId, MediaSessionEvent, TouchEventResult, ViewportDetails,
 };
 use euclid::default::Size2D as UntypedSize2D;
 use http::{HeaderMap, Method};
@@ -644,6 +644,11 @@ pub enum ScriptToConstellationMessage {
     IFrameSizes(Vec<IFrameSizeMsg>),
     /// Request results from the memory reporter.
     ReportMemory(IpcSender<MemoryReportResult>),
+    /// Return the result of the evaluated JavaScript with the given [`JavaScriptEvaluationId`].
+    FinishJavaScriptEvaluation(
+        JavaScriptEvaluationId,
+        Result<JSValue, JavaScriptEvaluationError>,
+    ),
 }
 
 impl fmt::Debug for ScriptToConstellationMessage {
diff --git a/components/shared/constellation/lib.rs b/components/shared/constellation/lib.rs
index 134eed6c1d9..d85fbe31bdf 100644
--- a/components/shared/constellation/lib.rs
+++ b/components/shared/constellation/lib.rs
@@ -19,8 +19,8 @@ use base::Epoch;
 use base::cross_process_instant::CrossProcessInstant;
 use base::id::{MessagePortId, PipelineId, WebViewId};
 use embedder_traits::{
-    CompositorHitTestResult, Cursor, InputEvent, MediaSessionActionType, Theme, ViewportDetails,
-    WebDriverCommandMsg,
+    CompositorHitTestResult, Cursor, InputEvent, JavaScriptEvaluationId, MediaSessionActionType,
+    Theme, ViewportDetails, WebDriverCommandMsg,
 };
 use euclid::Vector2D;
 pub use from_script_message::*;
@@ -92,6 +92,9 @@ pub enum EmbedderToConstellationMessage {
     SetScrollStates(PipelineId, Vec<ScrollState>),
     /// Notify the constellation that a particular paint metric event has happened for the given pipeline.
     PaintMetric(PipelineId, PaintMetricEvent),
+    /// Evaluate a JavaScript string in the context of a `WebView`. When execution is complete or an
+    /// error is encountered, a correpsonding message will be sent to the embedding layer.
+    EvaluateJavaScript(WebViewId, JavaScriptEvaluationId, String),
 }
 
 /// A description of a paint metric that is sent from the Servo renderer to the