Dump backtrace when cannot attach to observatory (#98550)

packages/flutter_tools/lib/src/ios/devices.dart

@@ -437,12 +437,12 @@ class IOSDevice extends Device {
       final Uri? localUri = await observatoryDiscovery?.uri;
       timer.cancel();
       if (localUri == null) {
-        iosDeployDebugger?.detach();
+        await iosDeployDebugger?.stopAndDumpBacktrace();
         return LaunchResult.failed();
       }
       return LaunchResult.succeeded(observatoryUri: localUri);
     } on ProcessException catch (e) {
-      iosDeployDebugger?.detach();
+      await iosDeployDebugger?.stopAndDumpBacktrace();
       _logger.printError(e.message);
       return LaunchResult.failed();
     } finally {

packages/flutter_tools/lib/src/ios/ios_deploy.dart

@@ -293,6 +293,15 @@ class IOSDeployDebugger {
   // (lldb) Process 6152 stopped
   static final RegExp _lldbProcessStopped = RegExp(r'Process \d* stopped');
 
+  // (lldb) Process 6152 detached
+  static final RegExp _lldbProcessDetached = RegExp(r'Process \d* detached');
+
+  // Send signal to stop (pause) the app. Used before a backtrace dump.
+  static const String _signalStop = 'process signal SIGSTOP';
+
+  // Print backtrace for all threads while app is stopped.
+  static const String _backTraceAll = 'thread backtrace all';
+
   /// Launch the app on the device, and attach the debugger.
   ///
   /// Returns whether or not the debugger successfully attached.
@@ -330,16 +339,41 @@ class IOSDeployDebugger {
           }
           return;
         }
-        if (line.contains('PROCESS_STOPPED') ||
-            line.contains('PROCESS_EXITED') ||
-            _lldbProcessExit.hasMatch(line) ||
-            _lldbProcessStopped.hasMatch(line)) {
+        if (line == _signalStop) {
+          // The app is about to be stopped. Only show in verbose mode.
+          _logger.printTrace(line);
+          return;
+        }
+        if (line == _backTraceAll) {
+          // The app is stopped and the backtrace for all threads will be printed.
+          _logger.printTrace(line);
+          // Even though we're not "detached", just stopped, mark as detached so the backtrace
+          // is only show in verbose.
+          _debuggerState = _IOSDeployDebuggerState.detached;
+          return;
+        }
+
+        if (line.contains('PROCESS_STOPPED') || _lldbProcessStopped.hasMatch(line)) {
+          // The app has been stopped. Dump the backtrace, and detach.
+          _logger.printTrace(line);
+          _iosDeployProcess?.stdin.writeln(_backTraceAll);
+          detach();
+          return;
+        }
+        if (line.contains('PROCESS_EXITED') || _lldbProcessExit.hasMatch(line)) {
           // The app exited or crashed, so exit. Continue passing debugging
           // messages to the log reader until it exits to capture crash dumps.
           _logger.printTrace(line);
           exit();
           return;
         }
+        if (_lldbProcessDetached.hasMatch(line)) {
+          // The debugger has detached from the app, and there will be no more debugging messages.
+          // Kill the ios-deploy process.
+          exit();
+          return;
+        }
+
         if (_debuggerState != _IOSDeployDebuggerState.attached) {
           _logger.printTrace(line);
           return;
@@ -395,6 +429,22 @@ class IOSDeployDebugger {
     return success;
   }
 
+  Future<void> stopAndDumpBacktrace() async {
+    if (!debuggerAttached) {
+      return;
+    }
+
+    try {
+      // Stop the app, which will prompt the backtrace to be printed for all threads in the stdoutSubscription handler.
+      _iosDeployProcess?.stdin.writeln(_signalStop);
+    } on SocketException catch (error) {
+      // Best effort, try to detach, but maybe the app already exited or already detached.
+      _logger.printTrace('Could not stop app from debugger: $error');
+    }
+    // Wait for logging to finish on process exit.
+    return logLines.drain();
+  }
+
   void detach() {
     if (!debuggerAttached) {
       return;
@@ -403,7 +453,6 @@ class IOSDeployDebugger {
     try {
       // Detach lldb from the app process.
       _iosDeployProcess?.stdin.writeln('process detach');
-      _debuggerState = _IOSDeployDebuggerState.detached;
     } on SocketException catch (error) {
       // Best effort, try to detach, but maybe the app already exited or already detached.
       _logger.printTrace('Could not detach from debugger: $error');

packages/flutter_tools/test/general.shard/ios/ios_deploy_test.dart

@@ -90,11 +90,14 @@ void main () {
         logger = BufferLogger.test();
       });
 
-      testWithoutContext('debugger attached', () async {
+      testWithoutContext('debugger attached and stopped', () async {
+        final StreamController<List<int>> stdin = StreamController<List<int>>();
+        final Stream<String> stdinStream = stdin.stream.transform<String>(const Utf8Decoder());
         final FakeProcessManager processManager = FakeProcessManager.list(<FakeCommand>[
-          const FakeCommand(
-            command: <String>['ios-deploy'],
-            stdout: '(lldb)     run\r\nsuccess\r\nsuccess\r\nLog on attach1\r\n\r\nLog on attach2\r\n\r\n\r\n\r\nPROCESS_STOPPED\r\nLog after process exit',
+          FakeCommand(
+            command: const <String>['ios-deploy'],
+            stdout: "(lldb)     run\r\nsuccess\r\nsuccess\r\nLog on attach1\r\n\r\nLog on attach2\r\n\r\n\r\n\r\nPROCESS_STOPPED\r\nLog after process stop\r\nthread backtrace all\r\n* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGSTOP",
+            stdin: IOSink(stdin.sink),
           ),
         ]);
         final IOSDeployDebugger iosDeployDebugger = IOSDeployDebugger.test(
@@ -113,7 +116,15 @@ void main () {
           'Log on attach2',
           '',
           '',
-          'Log after process exit',
+          'Log after process stop'
+        ]);
+        expect(logger.traceText, contains('PROCESS_STOPPED'));
+        expect(logger.traceText, contains('thread backtrace all'));
+        expect(logger.traceText, contains('* thread #1'));
+        expect(await stdinStream.take(3).toList(), <String>[
+          'thread backtrace all',
+          '\n',
+          'process detach',
         ]);
       });
 
@@ -141,11 +152,14 @@ void main () {
       });
 
       testWithoutContext('app crash', () async {
+        final StreamController<List<int>> stdin = StreamController<List<int>>();
+        final Stream<String> stdinStream = stdin.stream.transform<String>(const Utf8Decoder());
         final FakeProcessManager processManager = FakeProcessManager.list(<FakeCommand>[
-          const FakeCommand(
-            command: <String>['ios-deploy'],
+          FakeCommand(
+            command: const <String>['ios-deploy'],
             stdout:
-                '(lldb)     run\r\nsuccess\r\nLog on attach\r\n(lldb) Process 6156 stopped\r\n* thread #1, stop reason = Assertion failed:',
+                '(lldb)     run\r\nsuccess\r\nLog on attach\r\n(lldb) Process 6156 stopped\r\n* thread #1, stop reason = Assertion failed:\r\nthread backtrace all\r\n* thread #1, stop reason = Assertion failed:',
+            stdin: IOSink(stdin.sink),
           ),
         ]);
         final IOSDeployDebugger iosDeployDebugger = IOSDeployDebugger.test(
@@ -162,6 +176,14 @@ void main () {
           'Log on attach',
           '* thread #1, stop reason = Assertion failed:',
         ]);
+        expect(logger.traceText, contains('Process 6156 stopped'));
+        expect(logger.traceText, contains('thread backtrace all'));
+        expect(logger.traceText, contains('* thread #1'));
+        expect(await stdinStream.take(3).toList(), <String>[
+          'thread backtrace all',
+          '\n',
+          'process detach',
+        ]);
       });
 
       testWithoutContext('attach failed', () async {
@@ -268,6 +290,31 @@ void main () {
       iosDeployDebugger.detach();
       expect(await stdinStream.first, 'process detach');
     });
+
+    testWithoutContext('stop with backtrace', () async {
+      final StreamController<List<int>> stdin = StreamController<List<int>>();
+      final Stream<String> stdinStream = stdin.stream.transform<String>(const Utf8Decoder());
+      final FakeProcessManager processManager = FakeProcessManager.list(<FakeCommand>[
+        FakeCommand(
+          command: const <String>[
+            'ios-deploy',
+          ],
+          stdout:
+          '(lldb)     run\nsuccess\nLog on attach\n(lldb) Process 6156 stopped\n* thread #1, stop reason = Assertion failed:\n(lldb) Process 6156 detached',
+          stdin: IOSink(stdin.sink),
+        ),
+      ]);
+      final IOSDeployDebugger iosDeployDebugger = IOSDeployDebugger.test(
+        processManager: processManager,
+      );
+      await iosDeployDebugger.launchAndAttach();
+      await iosDeployDebugger.stopAndDumpBacktrace();
+      expect(await stdinStream.take(3).toList(), <String>[
+        'thread backtrace all',
+        '\n',
+        'process detach',
+      ]);
+    });
   });
 
   group('IOSDeploy.uninstallApp', () {