frindler · Jan 18, 2022
diff --git a/LibGit2Sharp.Tests/MergeFixture.cs b/LibGit2Sharp.Tests/MergeFixture.cs
@@ -902,6 +902,100 @@ public void CanIgnoreWhitespaceChangeMergeConflict(string branchName)
             }
         }
 
+        [Fact]
+        public void CanTreeMergeTreeIntoSameTree()
+        {
+            string path = SandboxMergeTestRepo();
+            using (var repo = new Repository(path))
+            {
+                var master = repo.Branches["master"].Tip;
+
+                var result = repo.ObjectDatabase.MergeTrees(master.Tree, master.Tree, master.Tree, null);
+                Assert.Equal(MergeTreeStatus.Succeeded, result.Status);
+                Assert.Empty(result.Conflicts);
+            }
+        }
+
+        [Fact]
+        public void CanTreeMergeFastForwardTreeWithoutConflicts()
+        {
+            string path = SandboxMergeTestRepo();
+            using (var repo = new Repository(path))
+            {
+                var master = repo.Lookup<Commit>("master");
+                var branch = repo.Lookup<Commit>("fast_forward");
+                var ancestor = repo.ObjectDatabase.FindMergeBase(master, branch);
+
+                var result = repo.ObjectDatabase.MergeTrees(ancestor.Tree, master.Tree, branch.Tree, null);
+                Assert.Equal(MergeTreeStatus.Succeeded, result.Status);
+                Assert.NotNull(result.Tree);
+                Assert.Empty(result.Conflicts);
+            }
+        }
+
+        [Fact]
+        public void CanIdentifyConflictsInMergeTrees()
+        {
+            string path = SandboxMergeTestRepo();
+            using (var repo = new Repository(path))
+            {
+                var master = repo.Lookup<Commit>("master");
+                var branch = repo.Lookup<Commit>("conflicts");
+                var ancestor = repo.ObjectDatabase.FindMergeBase(master, branch);
+
+                var result = repo.ObjectDatabase.MergeTrees(ancestor.Tree, master.Tree, branch.Tree, null);
+
+                Assert.Equal(MergeTreeStatus.Conflicts, result.Status);
+
+                Assert.Null(result.Tree);
+                Assert.Single(result.Conflicts);
+
+                var conflict = result.Conflicts.First();
+                Assert.Equal(new ObjectId("8e9daea300fbfef6c0da9744c6214f546d55b279"), conflict.Ancestor.Id);
+                Assert.Equal(new ObjectId("610b16886ca829cebd2767d9196f3c4378fe60b5"), conflict.Ours.Id);
+                Assert.Equal(new ObjectId("3dd9738af654bbf1c363f6c3bbc323bacdefa179"), conflict.Theirs.Id);
+            }
+        }
+
+        [Theory]
+        [InlineData("conflicts_spaces")]
+        [InlineData("conflicts_tabs")]
+        public void CanConflictOnWhitespaceChangeMergeTreesConflict(string branchName)
+        {
+            string path = SandboxMergeTestRepo();
+            using (var repo = new Repository(path))
+            {
+                var mergeResult = repo.Merge(branchName, Constants.Signature, new MergeOptions());
+                Assert.Equal(MergeStatus.Conflicts, mergeResult.Status);
+
+                var master = repo.Branches["master"].Tip;
+                var branch = repo.Branches[branchName].Tip;
+                var ancestor = repo.ObjectDatabase.FindMergeBase(master, branch);
+                var mergeTreeResult = repo.ObjectDatabase.MergeTrees(ancestor.Tree, master.Tree, branch.Tree, new MergeTreeOptions());
+                Assert.Equal(MergeTreeStatus.Conflicts, mergeTreeResult.Status);
+            }
+        }
+
+        [Theory]
+        [InlineData("conflicts_spaces")]
+        [InlineData("conflicts_tabs")]
+        public void CanIgnoreWhitespaceChangeMergeTreesConflict(string branchName)
+        {
+            string path = SandboxMergeTestRepo();
+            using (var repo = new Repository(path))
+            {
+                var mergeResult = repo.Merge(branchName, Constants.Signature, new MergeOptions() { IgnoreWhitespaceChange = true });
+                Assert.NotEqual(MergeStatus.Conflicts, mergeResult.Status);
+
+                var master = repo.Branches["master"].Tip;
+                var branch = repo.Branches[branchName].Tip;
+                var ancestor = repo.ObjectDatabase.FindMergeBase(master, branch);
+                var mergeTreeResult = repo.ObjectDatabase.MergeTrees(ancestor.Tree, master.Tree, branch.Tree, new MergeTreeOptions() { IgnoreWhitespaceChange = true });
+                Assert.NotEqual(MergeTreeStatus.Conflicts, mergeTreeResult.Status);
+                Assert.Empty(mergeTreeResult.Conflicts);
+            }
+        }
+
         [Fact]
         public void CanMergeIntoIndex()
         {

diff --git a/LibGit2Sharp/Core/NativeMethods.cs b/LibGit2Sharp/Core/NativeMethods.cs
@@ -1987,6 +1987,15 @@ internal static extern int git_transport_smart_credentials(
         internal static extern int git_transport_unregister(
             [MarshalAs(UnmanagedType.CustomMarshaler, MarshalCookie = UniqueId.UniqueIdentifier, MarshalTypeRef = typeof(StrictUtf8Marshaler))] string prefix);
 
+        [DllImport(libgit2, CallingConvention = CallingConvention.Cdecl)]
+        internal static extern unsafe int git_merge_trees(
+            out git_index* outIndex,
+            git_repository* repo,
+            git_object* ancestorTree,
+            git_object* ourTree,
+            git_object* theirTree,
+            ref GitMergeOpts options);
+
         [DllImport(libgit2, CallingConvention = CallingConvention.Cdecl)]
         internal static extern unsafe uint git_tree_entry_filemode(git_tree_entry* entry);
 

diff --git a/LibGit2Sharp/Core/Proxy.cs b/LibGit2Sharp/Core/Proxy.cs
@@ -3249,6 +3249,24 @@ public static int git_transport_smart_credentials(out IntPtr cred, IntPtr transp
 
 #region git_tree_
 
+        public static unsafe IndexHandle git_merge_trees(RepositoryHandle repo, ObjectHandle ancestorTree,
+            ObjectHandle ourTree, ObjectHandle theirTree, GitMergeOpts opts, out bool earlyStop)
+        {
+            git_index* index;
+            int res = NativeMethods.git_merge_trees(out index, repo, ancestorTree, ourTree, theirTree, ref opts);
+            if (res == (int)GitErrorCode.MergeConflict)
+            {
+                earlyStop = true;
+            }
+            else
+            {
+                earlyStop = false;
+                Ensure.ZeroResult(res);
+            }
+
+            return new IndexHandle(index, true);
+        }
+
         public static unsafe Mode git_tree_entry_attributes(git_tree_entry* entry)
         {
             return (Mode)NativeMethods.git_tree_entry_filemode(entry);

diff --git a/LibGit2Sharp/ObjectDatabase.cs b/LibGit2Sharp/ObjectDatabase.cs
@@ -808,6 +808,74 @@ public virtual MergeTreeResult MergeCommits(Commit ours, Commit theirs, MergeTre
             }
         }
 
+        /// <summary>
+        /// Perform a three-way merge of two trees relative to the provided ancestor.
+        /// The returned <see cref="MergeTreeResult"/> will contain the results
+        /// of the merge and can be examined for conflicts.
+        /// </summary>
+        /// <param name="ancestor">The ancestor tree</param>
+        /// <param name="ours">The first tree</param>
+        /// <param name="theirs">The second tree</param>
+        /// <param name="options">The <see cref="MergeTreeOptions"/> controlling the merge</param>
+        /// <returns>The <see cref="MergeTreeResult"/> containing the merged trees and any conflicts</returns>
+        public virtual MergeTreeResult MergeTrees(Tree ancestor, Tree ours, Tree theirs, MergeTreeOptions options)
+        {
+            Ensure.ArgumentNotNull(ancestor, "ancestor");
+            Ensure.ArgumentNotNull(ours, "ours");
+            Ensure.ArgumentNotNull(theirs, "theirs");
+
+            var modifiedOptions = new MergeTreeOptions();
+
+            // We throw away the index after looking at the conflicts, so we'll never need the REUC
+            // entries to be there
+            modifiedOptions.SkipReuc = true;
+
+            if (options != null)
+            {
+                modifiedOptions.FailOnConflict = options.FailOnConflict;
+                modifiedOptions.FindRenames = options.FindRenames;
+                modifiedOptions.IgnoreWhitespaceChange = options.IgnoreWhitespaceChange;
+                modifiedOptions.MergeFileFavor = options.MergeFileFavor;
+                modifiedOptions.RenameThreshold = options.RenameThreshold;
+                modifiedOptions.TargetLimit = options.TargetLimit;
+            }
+
+            bool earlyStop;
+            using (var indexHandle = MergeTrees(ancestor, ours, theirs, modifiedOptions, out earlyStop))
+            {
+                MergeTreeResult mergeResult;
+
+                // Stopped due to FailOnConflict so there's no index or conflict list
+                if (earlyStop)
+                {
+                    return new MergeTreeResult(new Conflict[] { });
+                }
+
+                if (Proxy.git_index_has_conflicts(indexHandle))
+                {
+                    List<Conflict> conflicts = new List<Conflict>();
+                    Conflict conflict;
+
+                    using (ConflictIteratorHandle iterator = Proxy.git_index_conflict_iterator_new(indexHandle))
+                    {
+                        while ((conflict = Proxy.git_index_conflict_next(iterator)) != null)
+                        {
+                            conflicts.Add(conflict);
+                        }
+                    }
+
+                    mergeResult = new MergeTreeResult(conflicts);
+                }
+                else
+                {
+                    var treeId = Proxy.git_index_write_tree_to(indexHandle, repo.Handle);
+                    mergeResult = new MergeTreeResult(this.repo.Lookup<Tree>(treeId));
+                }
+
+                return mergeResult;
+            }
+        }
+
         /// <summary>
         /// Packs all the objects in the <see cref="ObjectDatabase"/> and write a pack (.pack) and index (.idx) files for them.
         /// </summary>
@@ -940,6 +1008,50 @@ private IndexHandle MergeCommits(Commit ours, Commit theirs, MergeTreeOptions op
             }
         }
 
+        /// <summary>
+        /// Perform a three-way merge of two trees relative to the provided ancestor.
+        /// The returned <see cref="MergeTreeResult"/> will contain the results
+        /// of the merge and can be examined for conflicts.
+        /// </summary>
+        /// <param name="ancestor">The ancestor tree</param>
+        /// <param name="ours">The first tree</param>
+        /// <param name="theirs">The second tree</param>
+        /// <param name="options">The <see cref="MergeTreeOptions"/> controlling the merge</param>
+        /// <param name="earlyStop">True if the merge stopped early due to conflicts</param>
+        /// <returns>The <see cref="MergeTreeResult"/> containing the merged trees and any conflicts</returns>
+        private IndexHandle MergeTrees(Tree ancestor, Tree ours, Tree theirs, MergeTreeOptions options, out bool earlyStop)
+        {
+            GitMergeFlag mergeFlags = GitMergeFlag.GIT_MERGE_NORMAL;
+            if (options.SkipReuc)
+            {
+                mergeFlags |= GitMergeFlag.GIT_MERGE_SKIP_REUC;
+            }
+            if (options.FindRenames)
+            {
+                mergeFlags |= GitMergeFlag.GIT_MERGE_FIND_RENAMES;
+            }
+            if (options.FailOnConflict)
+            {
+                mergeFlags |= GitMergeFlag.GIT_MERGE_FAIL_ON_CONFLICT;
+            }
+
+            var mergeOptions = new GitMergeOpts
+            {
+                Version = 1,
+                MergeFileFavorFlags = options.MergeFileFavor,
+                MergeTreeFlags = mergeFlags,
+                RenameThreshold = (uint)options.RenameThreshold,
+                TargetLimit = (uint)options.TargetLimit,
+            };
+            using (var ancestorHandle = Proxy.git_object_lookup(repo.Handle, ancestor.Id, GitObjectType.Tree))
+            using (var oursHandle = Proxy.git_object_lookup(repo.Handle, ours.Id, GitObjectType.Tree))
+            using (var theirHandle = Proxy.git_object_lookup(repo.Handle, theirs.Id, GitObjectType.Tree))
+            {
+                var indexHandle = Proxy.git_merge_trees(repo.Handle, ancestorHandle, oursHandle, theirHandle, mergeOptions, out earlyStop);
+                return indexHandle;
+            }
+        }
+
         /// <summary>
         /// Performs a cherry-pick of <paramref name="cherryPickCommit"/> onto <paramref name="cherryPickOnto"/> commit.
         /// </summary>