Fix type errors in iOS simulator discovery. (#18960)

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

@@ -58,10 +58,7 @@ class SimControl {
 
   /// Runs `simctl list --json` and returns the JSON of the corresponding
   /// [section].
-  ///
-  /// The return type depends on the [section] being listed but is usually
-  /// either a [Map] or a [List].
-  dynamic _list(SimControlListSection section) {
+  Map<String, dynamic> _list(SimControlListSection section) {
     // Sample output from `simctl list --json`:
     //
     // {
@@ -97,9 +94,8 @@ class SimControl {
     final Map<String, dynamic> devicesSection = _list(SimControlListSection.devices);
 
     for (String deviceCategory in devicesSection.keys) {
-      final List<Map<String, String>> devicesData = devicesSection[deviceCategory];
-
-      for (Map<String, String> data in devicesData) {
+      final List<dynamic> devicesData = devicesSection[deviceCategory];
+      for (Map<String, dynamic> data in devicesData.map(_castStringKeyedMap)) {
         devices.add(new SimDevice(deviceCategory, data));
       }
     }
@@ -107,6 +103,11 @@ class SimControl {
     return devices;
   }
 
+  Map<String, dynamic> _castStringKeyedMap(dynamic untyped) {
+    final Map<dynamic, dynamic> map = untyped;
+    return map.cast<String, dynamic>();
+  }
+
   /// Returns all the connected simulator devices.
   List<SimDevice> getConnectedDevices() {
     return getDevices().where((SimDevice device) => device.isBooted).toList();
@@ -182,7 +183,7 @@ class SimDevice {
   SimDevice(this.category, this.data);
 
   final String category;
-  final Map<String, String> data;
+  final Map<String, dynamic> data;
 
   String get state => data['state'];
   String get availability => data['availability'];

packages/flutter_tools/test/ios/simulators_test.dart

@@ -329,4 +329,80 @@ void main() {
       ProcessManager: () => mockProcessManager,
     });
   });
+
+  group('SimControl', () {
+    const int mockPid = 123;
+    const String validSimControlOutput = '''
+{
+  "devices" : {
+    "watchOS 4.3" : [
+      {
+        "state" : "Shutdown",
+        "availability" : "(available)",
+        "name" : "Apple Watch - 38mm",
+        "udid" : "TEST-WATCH-UDID"
+      }
+    ],
+    "iOS 11.4" : [
+      {
+        "state" : "Booted",
+        "availability" : "(available)",
+        "name" : "iPhone 5s",
+        "udid" : "TEST-PHONE-UDID"
+      }
+    ],
+    "tvOS 11.4" : [
+      {
+        "state" : "Shutdown",
+        "availability" : "(available)",
+        "name" : "Apple TV",
+        "udid" : "TEST-TV-UDID"
+      }
+    ]
+  }
+}
+    ''';
+
+    MockProcessManager mockProcessManager;
+    SimControl simControl;
+
+    setUp(() {
+      mockProcessManager = new MockProcessManager();
+      when(mockProcessManager.runSync(any))
+          .thenReturn(new ProcessResult(mockPid, 0, validSimControlOutput, ''));
+
+      simControl = new SimControl();
+    });
+
+    testUsingContext('getDevices succeeds', () {
+      final List<SimDevice> devices = simControl.getDevices();
+
+      final SimDevice watch = devices[0];
+      expect(watch.category, 'watchOS 4.3');
+      expect(watch.state, 'Shutdown');
+      expect(watch.availability, '(available)');
+      expect(watch.name, 'Apple Watch - 38mm');
+      expect(watch.udid, 'TEST-WATCH-UDID');
+      expect(watch.isBooted, isFalse);
+
+      final SimDevice phone = devices[1];
+      expect(phone.category, 'iOS 11.4');
+      expect(phone.state, 'Booted');
+      expect(phone.availability, '(available)');
+      expect(phone.name, 'iPhone 5s');
+      expect(phone.udid, 'TEST-PHONE-UDID');
+      expect(phone.isBooted, isTrue);
+
+      final SimDevice tv = devices[2];
+      expect(tv.category, 'tvOS 11.4');
+      expect(tv.state, 'Shutdown');
+      expect(tv.availability, '(available)');
+      expect(tv.name, 'Apple TV');
+      expect(tv.udid, 'TEST-TV-UDID');
+      expect(tv.isBooted, isFalse);
+    }, overrides: <Type, Generator>{
+      ProcessManager: () => mockProcessManager,
+      SimControl: () => simControl,
+    });
+  });
 }