[DWDS] Don't send PauseInterrupted event during a hot reload (#2695)

Fixes dart-lang/sdk#61560

We rely on a pause within a hot reload to pause execution so that we can reregister breakpoints. However, the existing pause mechanism always sends a PauseInterrupted event, which then triggers the client to think this is a normal pause event and not an internal detail. Instead, we should have the ChromeProxyService signal to the debugger that this is an "internal pause" and therefore it should not send a regular pause event and should use a completer to signal the pause is done.

Tests are refactored and updated to correctly check for the events when reregistering breakpoints. Specifically, it checks no other events besides the expected ones are sent.

Author: srujzs

dwds/CHANGELOG.md

@@ -2,6 +2,7 @@
 
 - Bump SDK constraint to ^3.10.0
 - Added 'scriptUri' parameter to compileExpressionToJs
+- Fix an issue in `reloadSources` where a `PauseInterrupted` event was sent. - [#61560](https://github.com/dart-lang/sdk/issues/61560)
 
 ## 25.1.0
 

dwds/lib/src/debugging/debugger.dart

@@ -96,15 +96,28 @@ class Debugger extends Domain {
   bool _isStepping = false;
   DartLocation? _previousSteppingLocation;
 
+  // If not null and not completed, the pause handler completes this instead of
+  // sending a `PauseInterrupted` event to the event stream.
+  //
+  // In some cases e.g. a hot reload, DWDS pauses the execution itself in order
+  // to handle debugging logic like breakpoints. In such cases, sending the
+  // event to the event stream may trigger the client to believe that the user
+  // sent the event. To avoid that and still signal that a pause is completed,
+  // this completer is used. See https://github.com/dart-lang/sdk/issues/61560
+  // for more details.
+  Completer<void>? _internalPauseCompleter;
+
   void updateInspector(AppInspectorInterface appInspector) {
     inspector = appInspector;
     _breakpoints.inspector = appInspector;
   }
 
-  Future<Success> pause() async {
+  Future<Success> pause({bool internalPause = false}) async {
     _isStepping = false;
+    if (internalPause) _internalPauseCompleter = Completer<void>();
     final result = await _remoteDebugger.pause();
     handleErrorIfPresent(result);
+    await _internalPauseCompleter?.future;
     return Success();
   }
 
@@ -632,7 +645,14 @@ class Debugger extends Domain {
     // DevTools is showing an overlay. Both cannot be shown at the same time.
     // _showPausedOverlay();
     isolate.pauseEvent = event;
-    _streamNotify('Debug', event);
+    final internalPauseCompleter = _internalPauseCompleter;
+    if (event.kind == EventKind.kPauseInterrupted &&
+        internalPauseCompleter != null &&
+        !internalPauseCompleter.isCompleted) {
+      internalPauseCompleter.complete();
+    } else {
+      _streamNotify('Debug', event);
+    }
   }
 
   /// Handles resume events coming from the Chrome connection.