Fix hot restart so that it works with iOS simulators (#5272)

packages/flutter_tools/lib/src/hot.dart

@@ -38,10 +38,13 @@ class HotRunner extends ResidentRunner {
   }) : super(device,
              target: target,
              debuggingOptions: debuggingOptions,
-             usesTerminalUI: usesTerminalUI);
+             usesTerminalUI: usesTerminalUI) {
+    _projectRootPath = Directory.current.path;
+  }
 
   ApplicationPackage _package;
   String _mainPath;
+  String _projectRootPath;
   final AssetBundle bundle = new AssetBundle();
 
   /// Start the app and keep the process running during its lifetime.
@@ -202,13 +205,12 @@ class HotRunner extends ResidentRunner {
   }
 
   DevFS _devFS;
-  String _devFSProjectRootPath;
   Future<bool> _updateDevFS({ DevFSProgressReporter progressReporter }) async {
     if (_devFS == null) {
-      Directory directory = Directory.current;
-      _devFSProjectRootPath = directory.path;
-      String fsName = path.basename(directory.path);
-      _devFS = new DevFS(serviceProtocol, fsName, directory);
+      String fsName = path.basename(_projectRootPath);
+      _devFS = new DevFS(serviceProtocol,
+                         fsName,
+                         new Directory(_projectRootPath));
 
       try {
         await _devFS.create();
@@ -242,17 +244,10 @@ class HotRunner extends ResidentRunner {
     _devFS = null;
   }
 
-  Future<Null> _launchFromDevFS(ApplicationPackage package,
-                                String mainScript) async {
-    String entryPath = path.relative(mainScript, from: _devFSProjectRootPath);
-    String deviceEntryPath =
-        _devFS.baseUri.resolve(entryPath).toFilePath();
-    String devicePackagesPath =
-        _devFS.baseUri.resolve('.packages').toFilePath();
-    String deviceAssetsDirectoryPath =
-        _devFS.baseUri.resolve('build/flx').toFilePath();
+  Future<Null> _launchInView(String entryPath,
+                             String packagesPath,
+                             String assetsDirectoryPath) async {
     String viewId = await serviceProtocol.getFirstViewId();
-
     // When this completer completes the isolate is running.
     // TODO(johnmccutchan): Have the framework send an event after the first
     // frame is rendered and use that instead of 'runnable'.
@@ -267,20 +262,51 @@ class HotRunner extends ResidentRunner {
      }
     });
     await serviceProtocol.runInView(viewId,
-                                    deviceEntryPath,
-                                    devicePackagesPath,
-                                    deviceAssetsDirectoryPath);
+                                   entryPath,
+                                   packagesPath,
+                                   assetsDirectoryPath);
     await completer.future;
     await subscription.cancel();
   }
 
+  Future<Null> _launchFromDevFS(ApplicationPackage package,
+                                String mainScript) async {
+    String entryPath = path.relative(mainScript, from: _projectRootPath);
+    String deviceEntryPath =
+        _devFS.baseUri.resolve(entryPath).toFilePath();
+    String devicePackagesPath =
+        _devFS.baseUri.resolve('.packages').toFilePath();
+    String deviceAssetsDirectoryPath =
+        _devFS.baseUri.resolve('build/flx').toFilePath();
+    await _launchInView(deviceEntryPath,
+                        devicePackagesPath,
+                        deviceAssetsDirectoryPath);
+  }
+
+  Future<Null> _launchFromDisk(ApplicationPackage package,
+                               String mainScript) async {
+    Uri baseUri = new Uri.directory(_projectRootPath);
+    String entryPath = path.relative(mainScript, from: _projectRootPath);
+    String diskEntryPath = baseUri.resolve(entryPath).toFilePath();
+    String diskPackagesPath = baseUri.resolve('.packages').toFilePath();
+    String diskAssetsDirectoryPath = baseUri.resolve('build/flx').toFilePath();
+    await _launchInView(diskEntryPath,
+                        diskPackagesPath,
+                        diskAssetsDirectoryPath);
+  }
+
   Future<Null> _restartFromSources() async {
-    if (_devFS != null)
+    if (_devFS == null) {
+      Status restartStatus = logger.startProgress('Restarting application...');
+      await _launchFromDisk(_package, _mainPath);
+      restartStatus.stop(showElapsedTime: true);
+    } else {
       await _updateDevFS();
       Status restartStatus = logger.startProgress('Restarting application...');
       await _launchFromDevFS(_package, _mainPath);
       restartStatus.stop(showElapsedTime: true);
     }
+  }
 
   /// Returns [true] if the reload was successful.
   bool _printReloadReport(Map<String, dynamic> reloadReport) {