Merge pull request #54: Initial sparse implementation

Uses the code currently at microsoft/git#180. Covers the basics of #8.

* The default `scalar clone` runs `git sparse-checkout init` so the working directory only has files at root.

* Run `git sparse-checkout add <folders.txt` to pipe in a list of folders, and it will expand those files.

Example workflow:

```sh
$ scalar clone https://dev.azure.com/gvfs/ci/_git/ForTests
Clone parameters:
  Repo URL:     https://dev.azure.com/gvfs/ci/_git/ForTests
  Branch:       Default
  Cache Server: Default
  Local Cache:  C:\.scalarCache
  Destination:  C:\_git\test2\ForTests
Authenticating...Succeeded
Querying remote for config...Succeeded
Using cache server: None (https://dev.azure.com/gvfs/ci/_git/ForTests)

WARNING: Unable to validate your Scalar version
Server not configured to provide supported Scalar versions

Cloning...Succeeded
Fetching commits and trees from origin (no cache server)...Succeeded
Validating repo...Succeeded
Mounting...Succeeded

$ cd ForTests/src/
$ ls
AuthoringTests.md  GvFlt_EULA.md  GVFS.sln  License.md  nuget.config  Protocol.md  Readme.md  Settings.StyleCop

$ echo GVFS/GVFS.Common >>../folders.txt
$ echo GVFS/GVFS.UnitTests >>../folders.txt
$ echo GitHooksLoader >>../folders.txt
$ git sparse-checkout add <../folders.txt

$ ls
AuthoringTests.md  GitHooksLoader/  GvFlt_EULA.md  GVFS/  GVFS.sln  License.md  nuget.config  Protocol.md  Readme.md  Settings.StyleCop

$ echo GVFS/GVFS >>../folders2.txt
$ echo GVFS/GVFS.FunctionalTests >>../folders2.txt
$ git sparse-checkout add <../folders2.txt

$ ls
AuthoringTests.md  GitHooksLoader/  GvFlt_EULA.md  GVFS/  GVFS.sln  License.md  nuget.config  Protocol.md  Readme.md  Settings.StyleCop

$ ls GVFS
GVFS/  GVFS.Common/  GVFS.FunctionalTests/  GVFS.UnitTests/  LibGit2Sharp.NativeBinaries.props  ProjectedFSLib.NativeBinaries.props

$ git sparse-checkout list
/
/GVFS/
/GVFS/GVFS/*
/GVFS/GVFS.Common/*
/GVFS/GVFS.FunctionalTests/*
/GVFS/GVFS.UnitTests/*
/GitHooksLoader/*

```

I spun up a few remaining issues for follow-up work: #76, #77, #78.

Scalar.Build/Scalar.props

@@ -3,7 +3,7 @@
 
   <PropertyGroup Label="Parameters">
     <ScalarVersion>0.2.173.2</ScalarVersion>
-    <GitPackageVersion>2.20190820.1</GitPackageVersion>
+    <GitPackageVersion>2.20190822.3-sc</GitPackageVersion>
   </PropertyGroup>
 
   <PropertyGroup Label="DefaultSettings">

Scalar.Common/Git/GitProcess.cs

@@ -88,6 +88,11 @@ public static Result Init(Enlistment enlistment)
             return new GitProcess(enlistment).InvokeGitOutsideEnlistment("init \"" + enlistment.WorkingDirectoryBackingRoot + "\"");
         }
 
+        public static Result SparseCheckoutInit(Enlistment enlistment)
+        {
+            return new GitProcess(enlistment).InvokeGitInWorkingDirectoryRoot("sparse-checkout init --cone", useReadObjectHook: false);
+        }
+
         public static ConfigResult GetFromGlobalConfig(string gitBinPath, string settingName)
         {
             return new ConfigResult(

Scalar.FunctionalTests/Tests/EnlistmentPerFixture/PrefetchVerbTests.cs

@@ -45,34 +45,14 @@ public void PrefetchByFileExtension()
         }
 
         [TestCase, Order(4)]
-        public void PrefetchByFileExtensionWithHydrate()
-        {
-            int expectedCount = 3;
-            string output = this.Enlistment.Prefetch("--files *.md --hydrate");
-            this.ExpectBlobCount(output, expectedCount);
-            output.ShouldContain("Hydrated files:   " + expectedCount);
-        }
-
-        [TestCase, Order(5)]
-        public void PrefetchByFilesWithHydrateWhoseObjectsAreAlreadyDownloaded()
-        {
-            int expectedCount = 2;
-            string output = this.Enlistment.Prefetch(
-                $"--files {Path.Combine("GVFS", "GVFS", "Program.cs")};{Path.Combine("GVFS", "GVFS.FunctionalTests", "GVFS.FunctionalTests.csproj")} --hydrate");
-            this.ExpectBlobCount(output, expectedCount);
-            output.ShouldContain("Hydrated files:   " + expectedCount);
-            output.ShouldContain("Downloaded:       0");
-        }
-
-        [TestCase, Order(6)]
         public void PrefetchFolders()
         {
             this.ExpectBlobCount(this.Enlistment.Prefetch($"--folders {Path.Combine("GVFS", "GVFS")}"), 24);
             this.ExpectBlobCount(this.Enlistment.Prefetch($"--folders {Path.Combine("GVFS", "GVFS", "CommandLine")}"), 23);
             this.ExpectBlobCount(this.Enlistment.Prefetch($"--folders {Path.Combine("GVFS", "GVFS")};{Path.Combine("GVFS", "GVFS.FunctionalTests")}"), 72);
         }
 
-        [TestCase, Order(7)]
+        [TestCase, Order(5)]
         public void PrefetchNonExistentFilesAndFolders()
         {
             this.ExpectBlobCount(this.Enlistment.Prefetch("--files nonexistent.txt"), 0);
@@ -100,14 +80,14 @@ public void PrefetchFolderListFromFile()
             File.Delete(tempFilePath);
         }
 
-        [TestCase, Order(9)]
+        [TestCase, Order(6)]
         public void PrefetchAll()
         {
             this.ExpectBlobCount(this.Enlistment.Prefetch("--files *"), 494);
             this.ExpectBlobCount(this.Enlistment.Prefetch($"--folders {Path.DirectorySeparatorChar}"), 494);
         }
 
-        [TestCase, Order(10)]
+        [TestCase, Order(7)]
         public void NoopPrefetch()
         {
             this.ExpectBlobCount(this.Enlistment.Prefetch("--files *"), 494);
@@ -116,7 +96,7 @@ public void NoopPrefetch()
         }
 
         // TODO(#1219): Handle that lock files are not deleted on Mac, they are simply unlocked
-        [TestCase, Order(11)]
+        [TestCase, Order(8)]
         [Category(Categories.MacTODO.TestNeedsToLockFile)]
         public void PrefetchCleansUpStalePrefetchLock()
         {
@@ -139,7 +119,7 @@ public void PrefetchCleansUpStalePrefetchLock()
             prefetchCommitsLockFile.ShouldNotExistOnDisk(this.fileSystem);
         }
 
-        [TestCase, Order(12)]
+        [TestCase, Order(9)]
         public void PrefetchFilesFromFileListFile()
         {
             string tempFilePath = Path.Combine(Path.GetTempPath(), "temp.file");
@@ -161,7 +141,7 @@ public void PrefetchFilesFromFileListFile()
             }
         }
 
-        [TestCase, Order(13)]
+        [TestCase, Order(10)]
         public void PrefetchFilesFromFileListStdIn()
         {
             string input = string.Join(
@@ -175,7 +155,7 @@ public void PrefetchFilesFromFileListStdIn()
             this.ExpectBlobCount(this.Enlistment.Prefetch("--stdin-files-list", standardInput: input), 2);
         }
 
-        [TestCase, Order(14)]
+        [TestCase, Order(11)]
         public void PrefetchFolderListFromStdin()
         {
             string input = string.Join(

Scalar.FunctionalTests/Tools/ScalarProcess.cs

@@ -29,8 +29,9 @@ public ScalarProcess(string pathToScalar, string enlistmentRoot, string localCac
 
         public void Clone(string repositorySource, string branchToCheckout, bool skipPrefetch)
         {
+            // TODO: consider sparse clone for functional tests
             string args = string.Format(
-                "clone \"{0}\" \"{1}\" --branch \"{2}\" --local-cache-path \"{3}\" {4}",
+                "clone \"{0}\" \"{1}\" --full-clone --branch \"{2}\" --local-cache-path \"{3}\" {4}",
                 repositorySource,
                 this.enlistmentRoot,
                 branchToCheckout,

Scalar/CommandLine/CloneVerb.cs

@@ -67,6 +67,13 @@ public class CloneVerb : ScalarVerb
             HelpText = "Use this option to override the path for the local Scalar cache.")]
         public string LocalCacheRoot { get; set; }
 
+        [Option(
+            "full-clone",
+            Required = false,
+            Default = false,
+            HelpText = "When cloning, create full working directory.")]
+        public bool FullClone { get; set; }
+
         protected override string VerbName
         {
             get { return CloneVerbName; }
@@ -130,6 +137,7 @@ public override void Execute()
                                 { "Branch", this.Branch },
                                 { "LocalCacheRoot", this.LocalCacheRoot },
                                 { "SingleBranch", this.SingleBranch },
+                                { "FullClone", this.FullClone },
                                 { "NoPrefetch", this.NoPrefetch },
                                 { "Unattended", this.Unattended },
                                 { "IsElevated", ScalarPlatform.Instance.IsElevated() },
@@ -164,6 +172,7 @@ public override void Execute()
                         this.Output.WriteLine("  Cache Server: " + cacheServer);
                         this.Output.WriteLine("  Local Cache:  " + resolvedLocalCacheRoot);
                         this.Output.WriteLine("  Destination:  " + enlistment.EnlistmentRoot);
+                        this.Output.WriteLine("  FullClone:     " + this.FullClone);
 
                         string authErrorMessage;
                         if (!this.TryAuthenticate(tracer, enlistment, out authErrorMessage))
@@ -520,7 +529,7 @@ private Result CreateClone(
                 return new Result(installHooksError);
             }
 
-            // Place block below in an if statement when sparse clone is available.
+            if (this.FullClone)
             {
                 BlobPrefetcher prefetcher = new BlobPrefetcher(
                                                     tracer,
@@ -639,6 +648,17 @@ private Result TryInitRepo(ITracer tracer, GitRefs refs, Enlistment enlistmentTo
                 Path.Combine(repoPath, ScalarConstants.DotGit.PackedRefs),
                 refs.ToPackedRefs());
 
+            if (!this.FullClone)
+            {
+                GitProcess.Result sparseCheckoutResult = GitProcess.SparseCheckoutInit(enlistmentToInit);
+                if (sparseCheckoutResult.ExitCodeIsFailure)
+                {
+                    string error = string.Format("Could not init sparse-checkout at to {0}: {1}", repoPath, sparseCheckoutResult.Errors);
+                    tracer.RelatedError(error);
+                    return new Result(error);
+                }
+            }
+
             return new Result(true);
         }