Add ObjectDatabase.CreateGitLink()

Also, test manually adding new Submodule via TreeDefinition.

Author: dahlbyk

LibGit2Sharp.Tests/ObjectDatabaseFixture.cs

@@ -244,6 +244,52 @@ public void CanCreateATreeContainingABlobFromAFileInTheWorkingDirectory()
             }
         }
 
+        [Fact]
+        public void CanCreateATreeContainingAGitLinkFromAnUntrackedSubmoduleInTheWorkingDirectory()
+        {
+            string path = CloneSubmoduleTestRepo();
+            using (var repo = new Repository(path))
+            {
+                const string submodulePath = "sm_added_and_uncommited";
+
+                /* Unexpected behavior: test fails if this is uncommented... libgit2 caching?
+                var submoduleBefore = repo.Submodules[submodulePath];
+                Assert.NotNull(submoduleBefore);
+                Assert.Null(submoduleBefore.HeadCommitId);
+                /**/
+
+                var gitLink = repo.ObjectDatabase.CreateGitLink((ObjectId)"480095882d281ed676fe5b863569520e54a7d5c0");
+
+                TreeDefinition td = TreeDefinition.From(repo.Head.Tip.Tree)
+                                                  .Add(submodulePath, gitLink);
+
+                TreeEntryDefinition ted = td[submodulePath];
+                Assert.NotNull(ted);
+                Assert.Equal(Mode.GitLink, ted.Mode);
+                Assert.Equal(gitLink.Id, ted.TargetId);
+                Assert.Equal(GitObjectType.Commit, ted.Type);
+
+                Tree tree = repo.ObjectDatabase.CreateTree(td);
+
+                TreeEntry te = tree[submodulePath];
+                Assert.NotNull(te.Target);
+                Assert.IsType<GitLink>(te.Target);
+                Assert.Equal(gitLink.Id, te.Target.Id);
+
+                var commitWithSubmodule = repo.ObjectDatabase.CreateCommit("Submodule!", DummySignature, DummySignature, tree,
+                                                                           new[] { repo.Head.Tip });
+                repo.Reset(ResetOptions.Soft, commitWithSubmodule);
+
+                var submodule = repo.Submodules[submodulePath];
+                Assert.NotNull(submodule);
+                Assert.Equal(submodulePath, submodule.Name);
+                Assert.Equal(submodulePath, submodule.Path);
+
+                // This fails with HeadCommitId == null if lines above are uncommented
+                Assert.Equal(gitLink.Id, submodule.HeadCommitId);
+            }
+        }
+
         [Fact]
         public void CannotCreateATreeContainingABlobFromARelativePathAgainstABareRepository()
         {

LibGit2Sharp/ObjectDatabase.cs

@@ -118,6 +118,16 @@ public virtual Blob CreateBlob(BinaryReader reader, string hintpath = null)
             return repo.Lookup<Blob>(id);
         }
 
+        /// <summary>
+        ///   Creates a gitlink referencing the commit identified by <paramref name="objectId"/> in another repository.
+        /// </summary>
+        /// <param name="objectId">Identifier of the commit.</param>
+        /// <returns>The created <see cref = "GitLink"/>.</returns>
+        public virtual GitLink CreateGitLink(ObjectId objectId)
+        {
+            return new GitLink(repo, objectId);
+        }
+
         /// <summary>
         ///   Inserts a <see cref = "Tree"/> into the object database, created from a <see cref = "TreeDefinition"/>.
         /// </summary>