Fix finding git on mac and using the system git correctly

Author: shana

src/GitHub.Api/IO/NiceIO.cs

@@ -378,7 +378,7 @@ public override string ToString()
         public string ToString(SlashMode slashMode)
         {
             if (!_isInitialized)
-                return null;
+                return String.Empty;
 
             // Check if it's linux root /
             if (IsRoot && string.IsNullOrEmpty(_driveLetter))

src/GitHub.Api/Installer/GitInstaller.cs

@@ -44,7 +44,7 @@ public ITask<NPath> SetupGitIfNeeded()
             if (!environment.IsWindows)
             {
                 startTask = new FindExecTask("git", cancellationToken)
-                    .Configure(processManager);
+                    .Configure(processManager, false, true);
                 // we should doublecheck that system git is usable here
                 installationState = new GitInstallationState
                 {

src/GitHub.Api/OutputProcessors/IProcessManager.cs

@@ -4,7 +4,8 @@ namespace GitHub.Unity
 {
     public interface IProcessManager
     {
-        T Configure<T>(T processTask, NPath? executable = null, string arguments = null, NPath? workingDirectory = null, bool withInput = false)
+        T Configure<T>(T processTask, NPath? executable = null, string arguments = null, NPath? workingDirectory = null,
+        	bool withInput = false, bool dontSetupGit = false)
             where T : IProcess;
         IProcess Reconnect(IProcess processTask, int i);
         CancellationToken CancellationToken { get; }

src/GitHub.Api/OutputProcessors/ProcessManager.cs

@@ -23,7 +23,10 @@ public ProcessManager(IEnvironment environment, IProcessEnvironment gitEnvironme
             this.cancellationToken = cancellationToken;
         }
 
-        public T Configure<T>(T processTask, NPath? executable = null, string arguments = null, NPath? workingDirectory = null, bool withInput = false)
+        public T Configure<T>(T processTask, NPath? executable = null, string arguments = null,
+            NPath? workingDirectory = null,
+            bool withInput = false,
+            bool dontSetupGit = false)
              where T : IProcess
         {
             executable = executable ?? processTask.ProcessName?.ToNPath() ?? environment.GitExecutablePath;
@@ -42,7 +45,7 @@ public T Configure<T>(T processTask, NPath? executable = null, string arguments
                 StandardErrorEncoding = Encoding.UTF8
             };
 
-            gitEnvironment.Configure(startInfo, workingDirectory ?? environment.RepositoryPath);
+            gitEnvironment.Configure(startInfo, workingDirectory ?? environment.RepositoryPath, dontSetupGit);
 
             if (executable.Value.IsRelative)
             {

src/GitHub.Api/Platform/IProcessEnvironment.cs

@@ -4,6 +4,6 @@ namespace GitHub.Unity
 {
     public interface IProcessEnvironment
     {
-        void Configure(ProcessStartInfo psi, NPath workingDirectory);
+        void Configure(ProcessStartInfo psi, NPath workingDirectory, bool dontSetupGit = false);
     }
 }

src/GitHub.Api/Platform/ProcessEnvironment.cs

@@ -15,14 +15,14 @@ public ProcessEnvironment(IEnvironment environment)
             Environment = environment;
         }
 
-        public void Configure(ProcessStartInfo psi, NPath workingDirectory)
+        public void Configure(ProcessStartInfo psi, NPath workingDirectory, bool dontSetupGit = false)
         {
             psi.WorkingDirectory = workingDirectory;
             psi.EnvironmentVariables["HOME"] = NPath.HomeDirectory;
             psi.EnvironmentVariables["TMP"] = psi.EnvironmentVariables["TEMP"] = NPath.SystemTemp;
 
             // if we don't know where git is, then there's nothing else to configure
-            if (!Environment.GitInstallPath.IsInitialized)
+            if (!Environment.GitInstallPath.IsInitialized || dontSetupGit)
                 return;
 
 
@@ -52,7 +52,10 @@ public void Configure(ProcessStartInfo psi, NPath workingDirectory)
                     baseExecPath = baseExecPath.Combine("mingw64");
                 binPath = baseExecPath.Combine("bin");
             }
+
             var execPath = baseExecPath.Combine("libexec", "git-core");
+            if (!execPath.DirectoryExists())
+                execPath = NPath.Default;
 
             if (Environment.IsWindows)
             {
@@ -63,7 +66,9 @@ public void Configure(ProcessStartInfo psi, NPath workingDirectory)
             {
                 path = $"{gitExecutableDir}:{binPath}:{execPath}:{gitLfsPath}:{Environment.Path}:{developerPaths}";
             }
-            psi.EnvironmentVariables["GIT_EXEC_PATH"] = execPath.ToString();
+
+            if (execPath.IsInitialized)
+                psi.EnvironmentVariables["GIT_EXEC_PATH"] = execPath.ToString();
 
             psi.EnvironmentVariables["PATH"] = path;
             psi.EnvironmentVariables["GHU_FULLPATH"] = path;

src/GitHub.Api/Tasks/ProcessTask.cs

@@ -18,13 +18,20 @@ public static T Configure<T>(this T task, IProcessManager processManager, bool w
             return processManager.Configure(task, withInput: withInput);
         }
 
+        public static T Configure<T>(this T task, IProcessManager processManager, bool withInput, bool dontSetupGit)
+            where T : IProcess
+        {
+            return processManager.Configure(task, withInput: withInput, dontSetupGit: dontSetupGit);
+        }
+
         public static T Configure<T>(this T task, IProcessManager processManager, string executable = null,
             string arguments = null,
             NPath? workingDirectory = null,
-            bool withInput = false)
+            bool withInput = false
+            , bool dontSetupGit = false)
             where T : IProcess
         {
-            return processManager.Configure(task, executable?.ToNPath(), arguments, workingDirectory, withInput);
+            return processManager.Configure(task, executable?.ToNPath(), arguments, workingDirectory, withInput, dontSetupGit);
         }
     }