Adds Depth to FetchOptions allowing for shallow cloning (#2070)

* Added Depth as a fetch option

* Map Depth from FetchOptions to GitFetchOptions

* Added tests for shallow cloning

LibGit2Sharp.Tests/CloneFixture.cs

@@ -35,6 +35,34 @@ public void CanClone(string url)
             }
         }
 
+        [Theory]
+        [InlineData("https://github.com/libgit2/TestGitRepository",1)]
+        [InlineData("https://github.com/libgit2/TestGitRepository",5)]
+        [InlineData("https://github.com/libgit2/TestGitRepository",7)]
+        public void CanCloneShallow(string url, int depth)
+        {
+            var scd = BuildSelfCleaningDirectory();
+
+            var clonedRepoPath = Repository.Clone(url, scd.DirectoryPath, new CloneOptions
+            {
+                FetchOptions =
+                {
+                    Depth = depth,
+                },
+            });
+
+            using (var repo = new Repository(clonedRepoPath))
+            {
+                var commitsFirstParentOnly = repo.Commits.QueryBy(new CommitFilter
+                {
+                    FirstParentOnly = true,
+                });
+
+                Assert.Equal(depth, commitsFirstParentOnly.Count());
+                Assert.Equal("49322bb17d3acc9146f98c97d078513228bbf3c0", repo.Head.Tip.Id.ToString());
+            }
+        }
+
         [Theory]
         [InlineData("br2", "a4a7dce85cf63874e984719f4fdd239f5145052f")]
         [InlineData("packed", "41bc8c69075bbdb46c5c6f0566cc8cc5b46e8bd9")]

LibGit2Sharp/FetchOptions.cs

@@ -26,6 +26,14 @@ public sealed class FetchOptions : FetchOptionsBase
         /// </summary>
         public bool? Prune { get; set; }
 
+        /// <summary>
+        /// Specifies the depth of the fetch to perform.
+        /// <para>
+        /// Default value is 0 (full) fetch.
+        /// </para>
+        /// </summary>
+        public int Depth { get; set; } = 0;
+
         /// <summary>
         /// Get/Set the custom headers.
         ///

LibGit2Sharp/Repository.cs

@@ -780,6 +780,13 @@ public static string Clone(string sourceUrl, string workdirPath,
 
             options ??= new CloneOptions();
 
+            // As default behaviour for GitFetchOptionsWrapper ctor is to create
+            // a new instance of GitFetchOptions we only populate the Depth field.
+            var fetchOptions = new GitFetchOptions
+            {
+                Depth =  options.FetchOptions.Depth,
+            };
+
             // context variable that contains information on the repository that
             // we are cloning.
             var context = new RepositoryOperationContext(Path.GetFullPath(workdirPath), sourceUrl);
@@ -794,7 +801,7 @@ public static string Clone(string sourceUrl, string workdirPath,
             }
 
             using (var checkoutOptionsWrapper = new GitCheckoutOptsWrapper(options))
-            using (var fetchOptionsWrapper = new GitFetchOptionsWrapper())
+            using (var fetchOptionsWrapper = new GitFetchOptionsWrapper(fetchOptions))
             {
                 var gitCheckoutOptions = checkoutOptionsWrapper.Options;