devtools: Fix getBreakpointListActor handler in watcher actor (#38624)

the Firefox devtools client often sends multiple
`getBreakpointListActor` requests to the watcher actor when connecting,
and the Firefox devtools server returns the same breakpoint list actor
every time, but Servo returns a new breakpoint list actor each time.
this patch aligns Servo’s behaviour with Firefox.

Testing: this patch adds a devtools test

Signed-off-by: Delan Azabani <dazabani@igalia.com>
Co-authored-by: atbrakhi <atbrakhi@igalia.com>

components/devtools/actors/breakpoint.rs

@@ -52,4 +52,8 @@ impl BreakpointListActor {
     pub fn new(name: String) -> Self {
         Self { name }
     }
+
+    pub fn encodable(&self) -> BreakpointListActorMsg {
+        BreakpointListActorMsg { actor: self.name() }
+    }
 }

components/devtools/actors/watcher.rs

@@ -25,6 +25,7 @@ use super::breakpoint::BreakpointListActor;
 use super::thread::ThreadActor;
 use super::worker::WorkerMsg;
 use crate::actor::{Actor, ActorError, ActorRegistry};
+use crate::actors::breakpoint::BreakpointListActorMsg;
 use crate::actors::browsing_context::{BrowsingContextActor, BrowsingContextActorMsg};
 use crate::actors::root::RootActor;
 use crate::actors::watcher::target_configuration::{
@@ -151,12 +152,7 @@ struct GetThreadConfigurationActorReply {
 #[serde(rename_all = "camelCase")]
 struct GetBreakpointListActorReply {
     from: String,
-    breakpoint_list: GetBreakpointListActorReplyInner,
+    breakpoint_list: BreakpointListActorMsg,
-}
-
-#[derive(Serialize)]
-struct GetBreakpointListActorReplyInner {
-    actor: String,
 }
 
 #[derive(Serialize)]
@@ -191,6 +187,7 @@ pub struct WatcherActor {
     network_parent: String,
     target_configuration: String,
     thread_configuration: String,
+    breakpoint_list: String,
     session_context: SessionContext,
 }
 
@@ -376,15 +373,10 @@ impl Actor for WatcherActor {
                 request.reply_final(&msg)?
             },
             "getBreakpointListActor" => {
-                let breakpoint_list_name = registry.new_name("breakpoint-list");
+                let breakpoint_list = registry.find::<BreakpointListActor>(&self.breakpoint_list);
-                let breakpoint_list = BreakpointListActor::new(breakpoint_list_name.clone());
-                registry.register_later(Box::new(breakpoint_list));
-
                 request.reply_final(&GetBreakpointListActorReply {
                     from: self.name(),
-                    breakpoint_list: GetBreakpointListActorReplyInner {
+                    breakpoint_list: breakpoint_list.encodable(),
-                        actor: breakpoint_list_name,
-                    },
                 })?
             },
             _ => return Err(ActorError::UnrecognizedPacketType),
@@ -410,6 +402,7 @@ impl WatcherActor {
             TargetConfigurationActor::new(actors.new_name("target-configuration"));
         let thread_configuration =
             ThreadConfigurationActor::new(actors.new_name("thread-configuration"));
+        let breakpoint_list = BreakpointListActor::new(actors.new_name("breakpoint-list"));
 
         let watcher = Self {
             name: actors.new_name("watcher"),
@@ -417,12 +410,14 @@ impl WatcherActor {
             network_parent: network_parent.name(),
             target_configuration: target_configuration.name(),
             thread_configuration: thread_configuration.name(),
+            breakpoint_list: breakpoint_list.name(),
             session_context,
         };
 
         actors.register(Box::new(network_parent));
         actors.register(Box::new(target_configuration));
         actors.register(Box::new(thread_configuration));
+        actors.register(Box::new(breakpoint_list));
 
         watcher
     }

python/servo/devtools_tests.py

@@ -57,6 +57,16 @@ class DevtoolsTests(unittest.IsolatedAsyncioTestCase):
         self.web_servers = None
         self.web_server_threads = None
 
+    # Watcher tests
+
+    def test_watcher_returns_same_breakpoint_list_actor_every_time(self):
+        self.run_servoshell(url="data:text/html,")
+        devtools = self._setup_devtools_client()
+        response1 = devtools.watcher.get_breakpoint_list_actor()
+        response2 = devtools.watcher.get_breakpoint_list_actor()
+        self.assertEqual(response1["breakpointList"]["actor"], response2["breakpointList"]["actor"])
+
+    # Sources list
     # Classic script vs module script:
     # - <https://html.spec.whatwg.org/multipage/#classic-script>
     # - <https://html.spec.whatwg.org/multipage/#module-script>
@@ -66,8 +76,6 @@ class DevtoolsTests(unittest.IsolatedAsyncioTestCase):
     # Non-worker(?) script sources can be inline, external, or blob.
     # Worker script sources can be external or blob.
 
-    # Sources list
-
     def test_sources_list(self):
         self.start_web_server(test_dir=os.path.join(DevtoolsTests.script_path, "devtools_tests/sources"))
         self.run_servoshell()