Make Diff.Compare() able to compare null Trees

Author: nulltoken

LibGit2Sharp.Tests/DiffTreeToTreeFixture.cs

@@ -1,4 +1,5 @@
-using System.IO;
+using System;
+using System.IO;
 using System.Linq;
 using System.Text;
 using LibGit2Sharp.Tests.TestHelpers;
@@ -354,5 +355,39 @@ public void CanCompareTwoVersionsOfAFileWithADiffOfTwoHunks()
                 Assert.Equal(expected.ToString(), changes.Patch);
             }
         }
+
+        [Fact]
+        public void CanCompareATreeAgainstANullTree()
+        {
+            using (var repo = new Repository(StandardTestRepoPath))
+            {
+                Tree tree = repo.Branches["refs/remotes/origin/test"].Tip.Tree;
+
+                TreeChanges changes = repo.Diff.Compare(tree, null);
+
+                Assert.Equal(1, changes.Count());
+                Assert.Equal(1, changes.Deleted.Count());
+
+                Assert.Equal("readme.txt", changes.Deleted.Single().Path);
+
+                changes = repo.Diff.Compare(null, tree);
+
+                Assert.Equal(1, changes.Count());
+                Assert.Equal(1, changes.Added.Count());
+
+                Assert.Equal("readme.txt", changes.Added.Single().Path);
+            }
+        }
+
+        [Fact]
+        public void ComparingTwoNullTreesReturnsAnEmptyTreeChanges()
+        {
+            using (var repo = new Repository(StandardTestRepoPath))
+            {
+                TreeChanges changes = repo.Diff.Compare(null, null, null);
+
+                Assert.Equal(0, changes.Count());
+            }
+        }
     }
 }

LibGit2Sharp/Core/Handles/NullGitObjectSafeHandle.cs

@@ -0,0 +1,18 @@
+using System;
+
+namespace LibGit2Sharp.Core.Handles
+{
+    internal class NullGitObjectSafeHandle : GitObjectSafeHandle
+    {
+        public NullGitObjectSafeHandle()
+        {
+            handle = IntPtr.Zero;
+        }
+
+        protected override bool ReleaseHandle()
+        {
+            // Nothing to release
+            return true;
+        }
+    }
+}

LibGit2Sharp/Core/ObjectSafeWrapper.cs

@@ -7,12 +7,19 @@ internal class ObjectSafeWrapper : IDisposable
     {
         private readonly GitObjectSafeHandle objectPtr;
 
-        public ObjectSafeWrapper(ObjectId id, RepositorySafeHandle handle)
+        public ObjectSafeWrapper(ObjectId id, RepositorySafeHandle handle, bool allowNullObjectId = false)
         {
-            Ensure.ArgumentNotNull(id, "id");
             Ensure.ArgumentNotNull(handle, "handle");
 
-            objectPtr = Proxy.git_object_lookup(handle, id, GitObjectType.Any);
+            if (allowNullObjectId && id == null)
+            {
+                objectPtr = new NullGitObjectSafeHandle();
+            }
+            else
+            {
+                Ensure.ArgumentNotNull(id, "id");
+                objectPtr = Proxy.git_object_lookup(handle, id, GitObjectType.Any);
+            }
         }
 
         public GitObjectSafeHandle ObjectPtr

LibGit2Sharp/Core/Proxy.cs

@@ -550,8 +550,8 @@ public static DiffListSafeHandle git_diff_tree_to_tree(
             ObjectId newTree)
         {
             using (ThreadAffinity())
-            using (var osw1 = new ObjectSafeWrapper(oldTree, repo))
-            using (var osw2 = new ObjectSafeWrapper(newTree, repo))
+            using (var osw1 = new ObjectSafeWrapper(oldTree, repo, true))
+            using (var osw2 = new ObjectSafeWrapper(newTree, repo, true))
             {
                 DiffListSafeHandle diff;
                 int res = NativeMethods.git_diff_tree_to_tree(repo, options, osw1.ObjectPtr, osw2.ObjectPtr, out diff);

LibGit2Sharp/Diff.cs

@@ -70,11 +70,11 @@ internal Diff(Repository repo)
         /// <returns>A <see cref = "TreeChanges"/> containing the changes between the <paramref name = "oldTree"/> and the <paramref name = "newTree"/>.</returns>
         public virtual TreeChanges Compare(Tree oldTree, Tree newTree, IEnumerable<string> paths = null)
         {
-            Ensure.ArgumentNotNull(oldTree, "oldTree");
-            Ensure.ArgumentNotNull(oldTree, "newTree");
-
             using(GitDiffOptions options = BuildOptions(paths))
-            using (DiffListSafeHandle diff = BuildDiffListFromTrees(oldTree.Id, newTree.Id, options))
+            using (DiffListSafeHandle diff = BuildDiffListFromTrees(
+                oldTree != null ? oldTree.Id : null,
+                newTree != null ? newTree.Id : null,
+                options))
             {
                 return new TreeChanges(diff);
             }

LibGit2Sharp/LibGit2Sharp.csproj

@@ -74,6 +74,7 @@
     <Compile Include="Core\GitConfigEntry.cs" />
     <Compile Include="Core\GitObjectLazyGroup.cs" />
     <Compile Include="Core\GitTransferProgress.cs" />
+    <Compile Include="Core\Handles\NullGitObjectSafeHandle.cs" />
     <Compile Include="Core\ILazy.cs" />
     <Compile Include="Core\LazyGroup.cs" />
     <Compile Include="Core\Proxy.cs" />