Show a warning in the Dart Debug Extension when a user tries to debug a sharded Dart app

dwds/debug_extension/web/background.dart

@@ -38,6 +38,9 @@ const _allowedEvents = {'Overlay.inspectNodeRequested'};
 // Map of Chrome tab ID to encoded vm service protocol URI.
 final _tabIdToEncodedUri = <int, String>{};
 
+// Map of Chrome tab ID to warnings for that tab.
+final _tabIdToWarning = <int, String>{};
+
 final _debuggableTabs = <int>{};
 
 final _tabsToAttach = <Tab>{};
@@ -67,6 +70,12 @@ void main() {
     var callback = allowInterop((List<Tab> tabs) async {
       currentTab = tabs[0];
       if (!_debuggableTabs.contains(currentTab.id)) return;
+
+      if (_tabIdToWarning.containsKey(currentTab.id)) {
+        alert(_tabIdToWarning[currentTab.id]);
+        return;
+      }
+
       attach(Debuggee(tabId: currentTab.id), '1.3', allowInterop(() async {
         if (lastError != null) {
           String alertMessage;
@@ -100,6 +109,10 @@ void main() {
 
   onMessageAddListener(allowInterop(
       (Request request, Sender sender, Function sendResponse) async {
+    // Register any warnings for the tab:
+    if (request.warning != '') {
+      _tabIdToWarning[sender.tab.id] = request.warning;
+    }
     _debuggableTabs.add(sender.tab.id);
     _updateIcon();
     // TODO(grouma) - We can conditionally auto start debugging here.
@@ -362,9 +375,20 @@ void _updateIcon() {
   var query = QueryInfo(active: true, currentWindow: true);
   queryTabs(query, allowInterop((List tabs) {
     var tabList = List<Tab>.from(tabs);
-    if (tabList.isEmpty || _debuggableTabs.contains(tabList.first.id)) {
+    // If tabList is empty, the user has likely navigated to a different window.
+    // Therefore, do not update the icon:
+    if (tabList.isEmpty || tabList.first == null || tabList.first.id == null) {
+      return;
+    }
+
+    if (_tabIdToWarning.containsKey(tabList.first.id)) {
+      // Set the warning icon (red):
+      setIcon(IconInfo(path: 'dart_warning.png'));
+    } else if (_debuggableTabs.contains(tabList.first.id)) {
+      // Set the debuggable icon (blue):
       setIcon(IconInfo(path: 'dart.png'));
     } else {
+      // Set the default icon (grey):
       setIcon(IconInfo(path: 'dart_grey.png'));
     }
   }));
@@ -514,6 +538,7 @@ class Request {
   external int get tabId;
   external String get name;
   external dynamic get options;
+  external String get warning;
   external factory Request({int tabId, String name, dynamic options});
 }
 

dwds/debug_extension/web/content.js

@@ -1,39 +1,35 @@
-var hasSent = false;
+const MULTIPLE_APPS_ATTRIBUTE = 'data-multiple-dart-apps';
+
+const MULTIPLE_APPS_WARNING = 'It appears that you are running multiple Dart apps ' +
+    'and/or sub-apps. Dart debugging is currently not supported in a multi-app ' +
+    'environment.';
 
 function sendMessage(e) {
-    if (hasSent) return;
-    hasSent = true;
-    chrome.runtime.sendMessage(e, function (response) {
-    });
+    const hasMultipleApps = document
+        .documentElement
+        .getAttribute(MULTIPLE_APPS_ATTRIBUTE);
+    const warning = hasMultipleApps == 'true' ?  MULTIPLE_APPS_WARNING : '';
+    chrome.runtime.sendMessage(Object.assign(e, {warning: warning}));
 }
 
-document.addEventListener('dart-app-ready', function (e) {
+document.addEventListener('dart-app-ready', function(e) {
     sendMessage(e);
 });
 
-var targetNode = document.head;
-var observerOptions = {
-    childList: true,
-    attributes: true,
-    subtree: true
-};
 
-function callback(mutationList, observer) {
-    mutationList.forEach((mutation) => {
-        if (mutation.type == 'childList') {
-            var addedNodes = mutation.addedNodes
-            for (var i = 0; i < addedNodes.length; i++) {
-                if (addedNodes[i].tagName == 'SCRIPT' &&
-                    addedNodes[i].src.includes('dart_sdk.js')) {
-                    sendMessage({});
-                }
-            }
+function multipleDartAppsCallback(mutationList) {
+    mutationList.forEach(function(mutation) {
+        if (mutation.type !== "attributes") return;
+        if (mutation.attributeName === MULTIPLE_APPS_ATTRIBUTE) {
+            sendMessage({});
         }
     });
-}
+};
+
+// Watch for changes to the multiple apps data-attribute and update accordingly:
+var multipleDartAppsObserver = new MutationObserver(multipleDartAppsCallback);
+multipleDartAppsObserver.observe(document.documentElement, {
+    attributeFilter: [MULTIPLE_APPS_ATTRIBUTE]
+});
 
-// TODO(grouma) - This will become unnecessary when package:dwds version 11.0.0
-// hits Flutter stable.
-var observer = new MutationObserver(callback);
-observer.observe(targetNode, observerOptions);