Revert should clean up repository state when there is nothing to revert

LibGit2Sharp.Tests/RevertFixture.cs

@@ -391,5 +391,72 @@ public void CanNotRevertAMergeCommitWithoutSpecifyingTheMainlineBranch()
                 Assert.Throws<LibGit2SharpException>(() => repo.Revert(commitToRevert, Constants.Signature));
             }
         }
+
+        [Theory]
+        [InlineData(true)]
+        [InlineData(false)]
+        public void RevertWithNothingToRevert(bool commitOnSuccess)
+        {
+            // The branch name to perform the revert on
+            const string revertBranchName = "refs/heads/revert";
+
+            string path = CloneRevertTestRepo();
+            using (var repo = new Repository(path))
+            {
+                // Checkout the revert branch.
+                Branch branch = repo.Checkout(revertBranchName);
+                Assert.NotNull(branch);
+
+                Commit commitToRevert = repo.Head.Tip;
+
+                // Revert tip commit.
+                RevertResult result = repo.Revert(commitToRevert, Constants.Signature);
+                Assert.NotNull(result);
+                Assert.Equal(RevertStatus.Reverted, result.Status);
+
+                // Revert the same commit a second time
+                result = repo.Revert(
+                    commitToRevert,
+                    Constants.Signature,
+                    new RevertOptions() { CommitOnSuccess = commitOnSuccess });
+
+                Assert.NotNull(result);
+                Assert.Equal(null, result.Commit);
+                Assert.Equal(RevertStatus.NothingToRevert, result.Status);
+
+                if (commitOnSuccess)
+                {
+                    Assert.Equal(CurrentOperation.None, repo.Info.CurrentOperation);
+                }
+                else
+                {
+                    Assert.Equal(CurrentOperation.Revert, repo.Info.CurrentOperation);
+                }
+            }
+        }
+
+        [Fact]
+        public void RevertOrphanedBranchThrows()
+        {
+            // The branch name to perform the revert on
+            const string revertBranchName = "refs/heads/revert";
+
+            string path = CloneRevertTestRepo();
+            using (var repo = new Repository(path))
+            {
+                // Checkout the revert branch.
+                Branch branch = repo.Checkout(revertBranchName);
+                Assert.NotNull(branch);
+
+                Commit commitToRevert = repo.Head.Tip;
+
+                // Move the HEAD to an orphaned branch.
+                repo.Refs.UpdateTarget("HEAD", "refs/heads/orphan");
+                Assert.True(repo.Info.IsHeadUnborn);
+
+                // Revert the tip of the refs/heads/revert branch.
+                Assert.Throws<UnbornBranchException>(() => repo.Revert(commitToRevert, Constants.Signature));
+            }
+        }
     }
 }

LibGit2Sharp/Repository.cs

@@ -1084,6 +1084,14 @@ internal MergeResult MergeFetchHeads(Signature merger, MergeOptions options)
 
         /// <summary>
         /// Revert the specified commit.
+        /// <para>
+        ///  If the revert is successful but there are no changes to commit,
+        ///  then the <see cref="RevertStatus"/> will be <see cref="RevertStatus.NothingToRevert"/>.
+        ///  If the revert is successful and there are changes to revert, then
+        ///  the <see cref="RevertStatus"/> will be <see cref="RevertStatus.Reverted"/>.
+        ///  If the revert resulted in conflicts, then the <see cref="RevertStatus"/>
+        ///  will be <see cref="RevertStatus.Conflicts"/>.
+        /// </para>
         /// </summary>
         /// <param name="commit">The <see cref="Commit"/> to revert.</param>
         /// <param name="reverter">The <see cref="Signature"/> of who is performing the revert.</param>
@@ -1094,6 +1102,11 @@ public RevertResult Revert(Commit commit, Signature reverter, RevertOptions opti
             Ensure.ArgumentNotNull(commit, "commit");
             Ensure.ArgumentNotNull(reverter, "reverter");
 
+            if (Info.IsHeadUnborn)
+            {
+                throw new UnbornBranchException("Can not revert the commit. The Head doesn't point at a commit.");
+            }
+
             options = options ?? new RevertOptions();
 
             RevertResult result = null;
@@ -1123,12 +1136,38 @@ public RevertResult Revert(Commit commit, Signature reverter, RevertOptions opti
                 if (Index.IsFullyMerged)
                 {
                     Commit revertCommit = null;
+
+                    // Check if the revert generated any changes
+                    // and set the revert status accordingly
+                    bool anythingToRevert = Index.RetrieveStatus(
+                        new StatusOptions()
+                        {
+                            DetectRenamesInIndex = false,
+                            Show = StatusShowOption.IndexOnly
+                        }).Any();
+
+                    RevertStatus revertStatus = anythingToRevert ?
+                        RevertStatus.Reverted : RevertStatus.NothingToRevert;
+
                     if (options.CommitOnSuccess)
                     {
-                        revertCommit = this.Commit(Info.Message, author: reverter, committer: reverter);
+                        if (!anythingToRevert)
+                        {
+                            // If there were no changes to revert, and we are
+                            // asked to commit the changes, then cleanup
+                            // the repository state (following command line behavior).
+                            Proxy.git_repository_state_cleanup(handle);
+                        }
+                        else
+                        {
+                            revertCommit = this.Commit(
+                                Info.Message,
+                                author: reverter,
+                                committer: reverter);
+                        }
                     }
 
-                    result = new RevertResult(RevertStatus.Reverted, revertCommit);
+                    result = new RevertResult(revertStatus, revertCommit);
                 }
                 else
                 {

LibGit2Sharp/RevertOptions.cs

@@ -43,7 +43,17 @@ public RevertOptions()
         public CheckoutNotifyHandler OnCheckoutNotify { get; set; }
 
         /// <summary>
-        /// Commit the revert if the revert is successful.
+        /// Commit changes if there are no conflicts and the revert results
+        /// in changes.
+        /// <para>
+        ///  Following command line behavior, if the revert results in no
+        ///  changes, then Revert will cleanup the repository state if
+        ///  <see cref="CommitOnSuccess"/> is true (i.e. the repository
+        ///  will not be left in a "revert in progress" state).
+        ///  If <see cref="CommitOnSuccess"/> is false and there are no
+        ///  changes to revert, then the repository will be left in
+        ///  the "revert in progress" state.
+        /// </para>
         /// </summary>
         public bool CommitOnSuccess { get; set; }
 

LibGit2Sharp/RevertResult.cs

@@ -52,6 +52,11 @@ public enum RevertStatus
         /// <summary>
         /// The revert resulted in conflicts.
         /// </summary>
-        Conflicts
+        Conflicts,
+
+        /// <summary>
+        /// Revert was run, but there were no changes to commit.
+        /// </summary>
+        NothingToRevert,
     }
 }