[flutter tools] Improve messages when we fail to connect to the Observatory (#57355)

packages/flutter_tools/lib/src/vmservice.dart

@@ -89,13 +89,26 @@ Future<io.WebSocket> _defaultOpenChannel(String url, {
   io.WebSocket socket;
 
   Future<void> handleError(dynamic e) async {
-    globals.printTrace('Exception attempting to connect to Observatory: $e');
-    globals.printTrace('This was attempt #$attempts. Will retry in $delay.');
-
+    void Function(String) printVisibleTrace = globals.printTrace;
     if (attempts == 10) {
-      globals.printStatus('This is taking longer than expected...');
+      globals.printStatus('Connecting to the VM Service is taking longer than expected...');
+    } else if (attempts == 20) {
+      globals.printStatus('Still attempting to connect to the VM Service...');
+      globals.printStatus(
+        'If you do NOT see the Flutter application running, it might have '
+        'crashed. The device logs (e.g. from adb or XCode) might have more '
+        'details.');
+      globals.printStatus(
+        'If you do see the Flutter application running on the device, try '
+        're-running with --host-vmservice-port to use a specific port known to '
+        'be available.');
+    } else if (attempts % 50 == 0) {
+      printVisibleTrace = globals.printStatus;
     }
 
+    printVisibleTrace('Exception attempting to connect to the VM Service: $e');
+    printVisibleTrace('This was attempt #$attempts. Will retry in $delay.');
+
     // Delay next attempt.
     await Future<void>.delayed(delay);
 

packages/flutter_tools/test/general.shard/vmservice_test.dart

@@ -5,6 +5,7 @@
 import 'dart:async';
 
 import 'package:flutter_tools/src/base/common.dart';
+import 'package:flutter_tools/src/base/io.dart' as io;
 import 'package:flutter_tools/src/convert.dart';
 import 'package:vm_service/vm_service.dart' as vm_service;
 import 'package:mockito/mockito.dart';
@@ -12,6 +13,7 @@ import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/device.dart';
 import 'package:flutter_tools/src/version.dart';
 import 'package:flutter_tools/src/vmservice.dart';
+import 'package:quiver/testing/async.dart';
 
 import '../src/common.dart';
 import '../src/context.dart';
@@ -161,6 +163,38 @@ void main() {
     FlutterVersion: () => MockFlutterVersion(),
   });
 
+  testUsingContext('VMService prints messages for connection failures', () {
+    FakeAsync().run((FakeAsync time) {
+      final Uri uri = Uri.parse('ws://127.0.0.1:12345/QqL7EFEDNG0=/ws');
+      unawaited(connectToVmService(uri));
+
+      time.elapse(const Duration(seconds: 5));
+      expect(testLogger.statusText, isEmpty);
+
+      time.elapse(const Duration(minutes: 2));
+
+      final String statusText = testLogger.statusText;
+      expect(
+        statusText,
+        containsIgnoringWhitespace('Connecting to the VM Service is taking longer than expected...'),
+      );
+      expect(
+        statusText,
+        containsIgnoringWhitespace('try re-running with --host-vmservice-port'),
+      );
+      expect(
+        statusText,
+        containsIgnoringWhitespace('Exception attempting to connect to the VM Service:'),
+      );
+      expect(
+        statusText,
+        containsIgnoringWhitespace('This was attempt #50. Will retry'),
+      );
+    });
+  }, overrides: <Type, Generator>{
+    WebSocketConnector: () => failingWebSocketConnector,
+  });
+
   testWithoutContext('setAssetDirectory forwards arguments correctly', () async {
     final Completer<String> completer = Completer<String>();
     final vm_service.VmService  vmService = vm_service.VmService(
@@ -323,3 +357,11 @@ class MockFlutterVersion extends Mock implements FlutterVersion {
   @override
   Map<String, Object> toJson() => const <String, Object>{'Mock': 'Version'};
 }
+
+/// A [WebSocketConnector] that always throws an [io.SocketException].
+Future<io.WebSocket> failingWebSocketConnector(
+  String url, {
+  io.CompressionOptions compression,
+}) {
+  throw const io.SocketException('Failed WebSocket connection');
+}