update Android device detection to handle adb error messages (#6521)

packages/flutter_tools/lib/src/android/android_device.dart

@@ -629,18 +629,24 @@ final RegExp _kDeviceRegex = new RegExp(r'^(\S+)\s+(\S+)(.*)');
 /// [mockAdbOutput] is public for testing.
 List<AndroidDevice> getAdbDevices({ String mockAdbOutput }) {
   List<AndroidDevice> devices = <AndroidDevice>[];
-  List<String> output;
+  String text;
 
   if (mockAdbOutput == null) {
     String adbPath = getAdbPath(androidSdk);
     if (adbPath == null)
       return <AndroidDevice>[];
-    output = runSync(<String>[adbPath, 'devices', '-l']).trim().split('\n');
+    text = runSync(<String>[adbPath, 'devices', '-l']);
   } else {
-    output = mockAdbOutput.trim().split('\n');
+    text = mockAdbOutput;
   }
 
-  for (String line in output) {
+  // Check for error messages from adb
+  if (!text.contains('List of devices')) {
+    printError(text);
+    return <AndroidDevice>[];
+  }
+
+  for (String line in text.trim().split('\n')) {
     // Skip lines like: * daemon started successfully *
     if (line.startsWith('* daemon '))
       continue;

packages/flutter_tools/test/android_device_test.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter_tools/src/android/android_device.dart';
+import 'package:flutter_tools/src/base/logger.dart';
 import 'package:test/test.dart';
 
 import 'src/context.dart';
@@ -41,11 +42,25 @@ emulator-5612          host features:shell_2
 
     testUsingContext('android n', () {
       List<AndroidDevice> devices = getAdbDevices(mockAdbOutput: '''
+List of devices attached
 ZX1G22JJWR             device usb:3-3 product:shamu model:Nexus_6 device:shamu features:cmd,shell_v2
 ''');
       expect(devices, hasLength(1));
       expect(devices.first.name, 'Nexus 6');
     });
+
+    BufferLogger logger = new BufferLogger();
+    testUsingContext('adb error message', () {
+      List<AndroidDevice> devices = getAdbDevices(mockAdbOutput: '''
+It appears you do not have 'Android SDK Platform-tools' installed.
+Use the 'android' tool to install them:
+    android update sdk --no-ui --filter 'platform-tools'
+''');
+      expect(devices, hasLength(0));
+      expect(logger.errorText, contains('you do not have'));
+    }, overrides: <Type, dynamic>{
+      Logger : logger,
+    });
   });
 
   group('parseAdbDeviceProperties', () {