Merge pull request #239 from Workiva/unload-modules-loaded-after-unlo…

…ad-starts

Ensure all child modules get unloaded

lib/src/lifecycle_module.dart

@@ -1124,12 +1124,20 @@ abstract class LifecycleModule extends SimpleModule with Disposable {
       _activeSpan = _startTransitionSpan('unload');
 
       _willUnloadController.add(this);
-      await Future.wait(_childModules.toList().map((child) {
-        child.parentContext = _activeSpan?.context;
-        return child.unload().whenComplete(() {
-          child.parentContext = null;
-        });
-      }));
+
+      // We're looping here because it's possible for additional child modules to be added to this list while we are
+      // unloading the current items. While loadChildModule is guarded from adding new modules after unload starts,
+      // it contains asynchronous elements that allow a module to be added to this list during the unload.
+      // Note that items get removed from this list by an event handler listening to their didDispose stream.
+      while (_childModules.isNotEmpty) {
+        await Future.wait(_childModules.toList().map((child) {
+          child.parentContext = _activeSpan?.context;
+          return child.unload().whenComplete(() {
+            child.parentContext = null;
+          });
+        }));
+      }
+
       try {
         await onUnload();
       } catch (error, stackTrace) {