Support TreeEntry.Target for gitlink entries

Author: dahlbyk

LibGit2Sharp.Tests/SubmoduleFixture.cs

@@ -64,9 +64,17 @@ public void CanRetrieveTheCommitIdsOfASubmodule(string name, string headId, stri
                 Assert.Equal((ObjectId)headId, submodule.HeadCommitId);
                 Assert.Equal((ObjectId)indexId, submodule.IndexCommitId);
                 Assert.Equal((ObjectId)workDirId, submodule.WorkDirCommitId);
+
+                AssertEntryId((ObjectId)headId, repo.Head[name], c => c.Target.Id);
+                AssertEntryId((ObjectId)indexId, repo.Index[name], i => i.Id);
             }
         }
 
+        private static void AssertEntryId<T>(ObjectId expected, T entry, Func<T, ObjectId> selector)
+        {
+            Assert.Equal(expected, ReferenceEquals(entry, null) ? null : selector(entry));
+        }
+
         [Fact]
         public void CanEnumerateRepositorySubmodules()
         {

LibGit2Sharp/GitLink.cs

@@ -0,0 +1,27 @@
+using System.Diagnostics;
+
+namespace LibGit2Sharp
+{
+    /// <summary>
+    ///   Represents a gitlink (a reference to a commit in another Git repository)
+    /// </summary>
+    [DebuggerDisplay("{DebuggerDisplay,nq}")]
+    public class GitLink : GitObject
+    {
+        /// <summary>
+        ///   Needed for mocking purposes.
+        /// </summary>
+        protected GitLink()
+        { }
+
+        internal GitLink(Repository repo, ObjectId id)
+            : base(repo, id)
+        {
+        }
+
+        private string DebuggerDisplay
+        {
+            get { return Id.ToString(); }
+        }
+    }
+}

LibGit2Sharp/LibGit2Sharp.csproj

@@ -70,6 +70,7 @@
     <Compile Include="Conflict.cs" />
     <Compile Include="ConflictCollection.cs" />
     <Compile Include="Core\Handles\GitRefSpecHandle.cs" />
+    <Compile Include="GitLink.cs" />
     <Compile Include="UnmatchedPathException.cs" />
     <Compile Include="Core\Handles\ReflogEntrySafeHandle.cs" />
     <Compile Include="Core\Handles\ReflogSafeHandle.cs" />

LibGit2Sharp/TreeEntry.cs

@@ -72,12 +72,19 @@ internal ObjectId TargetId
 
         private GitObject RetrieveTreeEntryTarget()
         {
-            if (!Type.HasAny(new[]{GitObjectType.Tree, GitObjectType.Blob}))
+            switch (Type)
             {
-                throw new InvalidOperationException(string.Format(CultureInfo.InvariantCulture, "TreeEntry target of type '{0}' are not supported.", Type));
+                case GitObjectType.Commit:
+                    return new GitLink(repo, targetOid);
+                case GitObjectType.Blob:
+                case GitObjectType.Tree:
+                    return GitObject.BuildFrom(repo, targetOid, Type, Path);
+                default:
+                    throw new InvalidOperationException(
+                        string.Format(CultureInfo.InvariantCulture,
+                                      "TreeEntry target of type '{0}' is not supported.",
+                                      Type));
             }
-
-            return GitObject.BuildFrom(repo, targetOid, Type, Path);
         }
 
         /// <summary>