Bug 1588730 - Ensure calling form() before calling notifying onFront listeners. r=jdescottes

You can listen for fronts creation via `parentFront.onFront(typeName, callback)`.
For now, we were calling `callback` before we pass the `form` to Front.
This leads to empty attributes as the Front doesn't have access to any data.

Differential Revision: https://phabricator.services.mozilla.com/D49261

--HG--
extra : moz-landing-system : lando

devtools/server/tests/unit/test_protocol_onFront.js

@@ -24,6 +24,7 @@ const ChildActor = protocol.ActorClassWithSpec(childSpec, {
     return {
       actor: this.actorID,
       childID: this.childID,
+      foo: "bar",
     };
   },
 });
@@ -69,6 +70,7 @@ const RootActor = protocol.ActorClassWithSpec(rootSpec, {
 class ChildFront extends protocol.FrontClassWithSpec(childSpec) {
   form(form) {
     this.childID = form.childID;
+    this.foo = form.foo;
   }
 }
 protocol.registerFront(ChildFront);
@@ -94,6 +96,11 @@ add_task(async function run_test() {
 
   const fronts = [];
   rootFront.onFront("childActor", front => {
+    equal(
+      front.foo,
+      "bar",
+      "Front's form is set before onFront listeners are called"
+    );
     fronts.push(front);
   });
 

devtools/shared/protocol/Front.js

@@ -76,7 +76,7 @@ class Front extends Pool {
     this._beforeListeners = null;
   }
 
-  async manage(front) {
+  async manage(front, form, ctx) {
     if (!front.actorID) {
       throw new Error(
         "Can't manage front without an actor ID.\n" +
@@ -91,6 +91,15 @@ class Front extends Pool {
       await front.initialize();
     }
 
+    // Ensure calling form() *before* notifying about this front being just created.
+    // We exprect the front to be fully initialized, especially via its form attributes.
+    // But do that *after* calling manage() so that the front is already registered
+    // in Pools and can be fetched by its ID, in case a child actor, created in form()
+    // tries to get a reference to its parent via the actor ID.
+    if (form) {
+      front.form(form, ctx);
+    }
+
     // Call listeners registered via `onFront` method
     this._frontListeners.emit(front.typeName, front);
   }

devtools/shared/protocol/types.js

@@ -316,6 +316,15 @@ types.addActorType = function(name) {
       const actorID = typeof v === "string" ? v : v.actor;
       // `ctx.conn` is a DebuggerClient
       let front = ctx.conn.getFrontByID(actorID);
+
+      // When the type `${name}#actorid` is used, `v` is a string refering to the
+      // actor ID. We cannot read form information in this case and the actorID was
+      // already set when creating the front, so no need to do anything.
+      let form = null;
+      if (detail != "actorid") {
+        form = identityWrite(v);
+      }
+
       if (!front) {
         // If front isn't instantiated yet, create one.
         // Try lazy loading front if not already loaded.
@@ -333,14 +342,10 @@ types.addActorType = function(name) {
         const Class = type.frontClass;
         front = new Class(ctx.conn, targetFront, parentFront);
         front.actorID = actorID;
-        parentFront.manage(front);
-      }
 
-      // When the type `${name}#actorid` is used, `v` is a string refering to the
-      // actor ID. We only set the actorID just before and so do not need anything else.
-      if (detail != "actorid") {
-        v = identityWrite(v);
-        front.form(v, ctx);
+        parentFront.manage(front, form, ctx);
+      } else if (form) {
+        front.form(form, ctx);
       }
 
       return front;