fix(modules): Immediately resolve follow-up dyn imports to a dyn imported module (#14958)

When a dynamically imported module gets resolved, any code that comes after an
await import() to that module will continue running. However, if that is the
last code in the evaluation of another dynamically imported module, that second
module will not resolve until the next iteration of the event loop, even though
it does not depend on the event loop at all.

When the event loop is being blocked by a long-running operation, such as a
long-running timer, or by an async op that might never end, such as with workers
or BroadcastChannels, that will result in the second dynamically imported module
not being resolved for a while, or ever.

This change fixes this by running the dynamic module loading steps in a loop
until no more dynamic modules can be resolved.

1 files changed, 25 insertions, 6 deletions

diff --git a/core/runtime.rs b/core/runtime.rs
index 97c822848..f82f06207 100644
--- a/core/runtime.rs
+++ b/core/runtime.rs
@@ -886,13 +886,28 @@ impl JsRuntime {
 
     // Dynamic module loading - ie. modules loaded using "import()"
     {
-      let poll_imports = self.prepare_dyn_imports(cx)?;
-      assert!(poll_imports.is_ready());
+      // Run in a loop so that dynamic imports that only depend on another
+      // dynamic import can be resolved in this event loop iteration.
+      //
+      // For example, a dynamically imported module like the following can be
+      // immediately resolved after `dependency.ts` is fully evaluated, but it
+      // wouldn't if not for this loop.
+      //
+      //    await delay(1000);
+      //    await import("./dependency.ts");
+      //    console.log("test")
+      //
+      loop {
+        let poll_imports = self.prepare_dyn_imports(cx)?;
+        assert!(poll_imports.is_ready());
 
-      let poll_imports = self.poll_dyn_imports(cx)?;
-      assert!(poll_imports.is_ready());
+        let poll_imports = self.poll_dyn_imports(cx)?;
+        assert!(poll_imports.is_ready());
 
-      self.evaluate_dyn_imports();
+        if !self.evaluate_dyn_imports() {
+          break;
+        }
+      }
 
       self.check_promise_exceptions()?;
     }
@@ -1505,7 +1520,9 @@ impl JsRuntime {
     }
   }
 
-  fn evaluate_dyn_imports(&mut self) {
+  // Returns true if some dynamic import was resolved.
+  fn evaluate_dyn_imports(&mut self) -> bool {
+    let mut resolved_any = false;
     let state_rc = Self::state(self.v8_isolate());
     let mut still_pending = vec![];
     let pending =
@@ -1536,6 +1553,7 @@ impl JsRuntime {
       };
 
       if let Some(result) = maybe_result {
+        resolved_any = true;
         match result {
           Ok((dyn_import_id, module_id)) => {
             self.dynamic_import_resolve(dyn_import_id, module_id);
@@ -1547,6 +1565,7 @@ impl JsRuntime {
       }
     }
     state_rc.borrow_mut().pending_dyn_mod_evaluate = still_pending;
+    resolved_any
   }
 
   /// Asynchronously load specified module and all of its dependencies.