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.

cli/tests/integration/run_tests.rs

@@ -2733,3 +2733,8 @@ itest!(test_and_bench_are_noops_in_run {
   args: "run test_and_bench_in_run.js",
   output_str: Some(""),
 });
+
+itest!(followup_dyn_import_resolved {
+  args: "run --unstable --allow-read followup_dyn_import_resolves/main.ts",
+  output: "followup_dyn_import_resolves/main.ts.out",
+});

cli/tests/testdata/followup_dyn_import_resolves/main.ts

@@ -0,0 +1,14 @@
+// https://github.com/denoland/deno/issues/14726
+
+// Any dynamic modules that are only pending on a TLA import should be resolved
+// in the same event loop iteration as the imported module.
+
+// Long-running timer so the event loop doesn't have a next iteration for a
+// while.
+setTimeout(() => {}, 24 * 60 * 60 * 1000);
+
+await import("./sub1.ts");
+
+// If we reach here, the test is passed.
+console.log("Done.");
+Deno.exit();

cli/tests/testdata/followup_dyn_import_resolves/main.ts.out

@@ -0,0 +1,3 @@
+sub2
+sub1
+Done.

cli/tests/testdata/followup_dyn_import_resolves/sub1.ts

@@ -0,0 +1,2 @@
+await import("./sub2.ts");
+console.log("sub1");

cli/tests/testdata/followup_dyn_import_resolves/sub2.ts

@@ -0,0 +1 @@
+console.log("sub2");

core/modules.rs

@@ -1803,15 +1803,11 @@ import "/a.js";
         )
         .unwrap();
 
-      // First poll runs `prepare_load` hook.
-      assert!(matches!(runtime.poll_event_loop(cx, false), Poll::Pending));
-      assert_eq!(prepare_load_count.load(Ordering::Relaxed), 1);
-
-      // Second poll actually loads modules into the isolate.
       assert!(matches!(
         runtime.poll_event_loop(cx, false),
         Poll::Ready(Ok(_))
       ));
+      assert_eq!(prepare_load_count.load(Ordering::Relaxed), 1);
       assert_eq!(resolve_count.load(Ordering::Relaxed), 7);
       assert_eq!(load_count.load(Ordering::Relaxed), 1);
       assert!(matches!(

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.