script: Queue a microtask in wait_for_all of promise type (#39108)

In the wait-for-all algorithm of the IDL promise type, we need to queue
a microtask to perform successSteps given « » if total is 0.

This step was previously implemented in a workaround, which perform
successSteps immediately.

This patch properly queue the microtask, and remove the workaround.

Testing: Refactoring only. Existing tests are enough.
Fixes: #37259

---------

Signed-off-by: Kingsley Yung <kingsley@kkoyung.dev>

components/script/dom/promise.rs

@@ -35,10 +35,11 @@ use script_bindings::conversions::SafeToJSValConvertible;
 use crate::dom::bindings::conversions::root_from_object;
 use crate::dom::bindings::error::{Error, ErrorToJsval};
 use crate::dom::bindings::reflector::{DomGlobal, DomObject, MutDomObject, Reflector};
-use crate::dom::bindings::root::AsHandleValue;
+use crate::dom::bindings::root::{AsHandleValue, DomRoot};
 use crate::dom::bindings::settings_stack::AutoEntryScript;
 use crate::dom::globalscope::GlobalScope;
 use crate::dom::promisenativehandler::{Callback, PromiseNativeHandler};
+use crate::microtask::{Microtask, MicrotaskRunnable};
 use crate::realms::{AlreadyInRealm, InRealm, enter_realm};
 use crate::script_runtime::{CanGc, JSContext as SafeJSContext};
 use crate::script_thread::ScriptThread;
@@ -490,6 +491,27 @@ impl Callback for WaitForAllRejectionHandler {
     }
 }
 
+/// The microtask for performing successSteps given « » in
+/// <https://webidl.spec.whatwg.org/#wait-for-all>.
+#[derive(JSTraceable, MallocSizeOf)]
+pub(crate) struct WaitForAllSuccessStepsMicrotask {
+    global: DomRoot<GlobalScope>,
+
+    #[ignore_malloc_size_of = "Closure is hard"]
+    #[no_trace]
+    success_steps: WaitForAllSuccessSteps,
+}
+
+impl MicrotaskRunnable for WaitForAllSuccessStepsMicrotask {
+    fn handler(&self, _can_gc: CanGc) {
+        (self.success_steps)(vec![]);
+    }
+
+    fn enter_realm(&self) -> JSAutoRealm {
+        enter_realm(&*self.global)
+    }
+}
+
 /// <https://webidl.spec.whatwg.org/#wait-for-all>
 #[cfg_attr(crown, allow(crown::unrooted_must_root))]
 pub(crate) fn wait_for_all(
@@ -521,8 +543,19 @@ pub(crate) fn wait_for_all(
     // Note: done using the len of result.
 
     // If total is 0, then:
+    if promises.is_empty() {
         // Queue a microtask to perform successSteps given « ».
-    // TODO: #37259
+        global.microtask_queue().enqueue(
+            Microtask::WaitForAllSuccessSteps(WaitForAllSuccessStepsMicrotask {
+                global: DomRoot::from_ref(global),
+                success_steps,
+            }),
+            cx,
+        );
+
+        // Return.
+        return;
+    }
 
     // Let index be 0.
     // Note: done with `enumerate` below.
@@ -594,15 +627,6 @@ pub(crate) fn wait_for_all_promise(
         failure_promise.reject_native(&reason, can_gc);
     });
 
-    if promises.is_empty() {
-        // Note: part of `wait_for_all`.
-        // Done here by using `resolve_native`.
-        // TODO: #37259
-        // If total is 0, then:
-        // Queue a microtask to perform successSteps given « ».
-        let empty_list: Vec<HandleValue> = vec![];
-        promise.resolve_native(&empty_list, can_gc);
-    } else {
     // Wait for all with promises, given successSteps and failureSteps.
     wait_for_all(
         cx,
@@ -613,7 +637,6 @@ pub(crate) fn wait_for_all_promise(
         realm,
         can_gc,
     );
-    }
 
     // Return promise.
     promise

components/script/microtask.rs

@@ -23,6 +23,7 @@ use crate::dom::globalscope::GlobalScope;
 use crate::dom::html::htmlimageelement::ImageElementMicrotask;
 use crate::dom::html::htmlmediaelement::MediaElementMicrotask;
 use crate::dom::mutationobserver::MutationObserver;
+use crate::dom::promise::WaitForAllSuccessStepsMicrotask;
 use crate::realms::enter_realm;
 use crate::script_runtime::{CanGc, JSContext, notify_about_rejected_promises};
 use crate::script_thread::ScriptThread;
@@ -43,6 +44,7 @@ pub(crate) enum Microtask {
     MediaElement(MediaElementMicrotask),
     ImageElement(ImageElementMicrotask),
     ReadableStreamTeeReadRequest(DefaultTeeReadRequestMicrotask),
+    WaitForAllSuccessSteps(WaitForAllSuccessStepsMicrotask),
     CustomElementReaction,
     NotifyMutationObservers,
 }
@@ -141,16 +143,20 @@ impl MicrotaskQueue {
                         let _realm = task.enter_realm();
                         task.handler(can_gc);
                     },
+                    Microtask::ReadableStreamTeeReadRequest(ref task) => {
+                        let _realm = task.enter_realm();
+                        task.handler(can_gc);
+                    },
+                    Microtask::WaitForAllSuccessSteps(ref task) => {
+                        let _realm = task.enter_realm();
+                        task.handler(can_gc);
+                    },
                     Microtask::CustomElementReaction => {
                         ScriptThread::invoke_backup_element_queue(can_gc);
                     },
                     Microtask::NotifyMutationObservers => {
                         MutationObserver::notify_mutation_observers(can_gc);
                     },
-                    Microtask::ReadableStreamTeeReadRequest(ref task) => {
-                        let _realm = task.enter_realm();
-                        task.handler(can_gc);
-                    },
                 }
             }
         }