Find Git using where and use Resource string

Check that Git.exe can be found and show error from resource string if it can't.

Author: jcansdale

src/GitHub.App/Resources.Designer.cs

@@ -288,4 +288,10 @@
   <data name="SyncSubmodules" xml:space="preserve">
     <value>Sync {0} submodules</value>
   </data>
+  <data name="CouldntFindGitOnPath" xml:space="preserve">
+    <value>Couldn't find Git.exe on PATH.
+
+Please install Git for Windows from:
+https://git-scm.com/download/win</value>
+  </data>
 </root>

src/GitHub.App/Resources.resx

@@ -191,23 +191,18 @@ public IObservable<Unit> SyncSubmodules(ILocalRepositoryModel repository)
         {
             return Observable.Defer(async () =>
             {
+                var exitCode = Where("git");
+                if (exitCode != 0)
+                {
+                    var ex = new ApplicationException(App.Resources.CouldntFindGitOnPath);
+                    return Observable.Throw<Unit>(ex);
+                }
+
                 var output = new StringWriter(CultureInfo.InvariantCulture);
-                var exitCode = await SyncSubmodules(repository.LocalPath, line => output.WriteLine(line));
+                exitCode = await SyncSubmodules(repository.LocalPath, line => output.WriteLine(line));
                 if (exitCode != 0)
                 {
-                    // Replace with friendly message if Git.exe isn't on path.
-                    // If culture isn't English, user will see the local equivalent of:
-                    // "'git' is not recognized as an internal or external command"                    
                     var message = output.ToString();
-                    if (exitCode == 1 && message.StartsWith("'git' is not recognized as an internal or external command,", StringComparison.Ordinal))
-                    {
-                        message =
-@"Couldn't find Git.exe on PATH.
-
-Please install Git for Windows from:
-https://git-scm.com/download/win";
-                    }
-
                     var ex = new ApplicationException(message);
                     return Observable.Throw<Unit>(ex);
                 }
@@ -239,6 +234,22 @@ await Task.WhenAll(
             }
         }
 
+        static int Where(string fileName)
+        {
+            var cmdArguments = "/C WHERE /Q " + fileName;
+            var startInfo = new ProcessStartInfo("cmd", cmdArguments)
+            {
+                UseShellExecute = false,
+                CreateNoWindow = true
+            };
+
+            using (var process = Process.Start(startInfo))
+            {
+                process.WaitForExit();
+                return process.ExitCode;
+            }
+        }
+
         static async Task ReadLinesAsync(TextReader reader, Action<string> progress)
         {
             string line;