Map rewritten parents to rewritten commits

LibGit2Sharp.Tests/FilterBranchFixture.cs

@@ -315,6 +315,51 @@ namespace LibGit2Sharp.Tests
             Assert.True(hasBeenCalled);
         }
 
+        // Graft the orphan "test" branch to the tip of "packed"
+        //
+        // Before:
+        // * e90810b  (test, lw, e90810b, test)
+        // |
+        // * 6dcf9bf
+        //     <------------------ note: no connection
+        // * 41bc8c6  (packed)
+        // |
+        // * 5001298
+        //
+        // ... and after:
+        //
+        // * f558880  (test, lw, e90810b, test)
+        // |
+        // * 0c25efa
+        // |   <------------------ add this link
+        // * 41bc8c6  (packed)
+        // |
+        // * 5001298
+        [Fact]
+        public void CanRewriteParentWithRewrittenCommit()
+        {
+            var commitToRewrite = repo.Lookup<Commit>("6dcf9bf");
+            var newParent = repo.Lookup<Commit>("41bc8c6");
+
+            repo.Refs.RewriteHistory(new RewriteHistoryOptions
+            {
+                CommitHeaderRewriter =
+                    c =>
+                    c.Id != newParent.Id
+                        ? null
+                        : CommitRewriteInfo.From(c, message: "changed"),
+                CommitParentsRewriter =
+                    c =>
+                    c.Id != commitToRewrite.Id
+                        ? c.Parents
+                        : new[] { newParent }
+            }, commitToRewrite, newParent);
+
+            var rewrittenParent = repo.Lookup<Commit>("refs/heads/test~").Parents.Single();
+            Assert.Equal(newParent.Tree, rewrittenParent.Tree);
+            Assert.NotEqual(newParent, rewrittenParent);
+        }
+
         [Fact]
         public void WritesCorrectReflogMessagesForSimpleRewrites()
         {

LibGit2Sharp/Core/HistoryRewriter.cs

@@ -127,12 +127,7 @@ namespace LibGit2Sharp.Core
             var newTree = commit.Tree;
 
             // Find the new parents
-            var newParents = commit.Parents
-                .Select(oldParent =>
-                        shaMap.ContainsKey(oldParent.Id)
-                            ? shaMap[oldParent.Id]
-                            : oldParent.Id)
-                .Select(id => repo.Lookup<Commit>(id));
+            var newParents = commit.Parents;
 
             if (targetedCommits.Contains(commit))
             {
@@ -157,6 +152,13 @@ namespace LibGit2Sharp.Core
             }
 
             // Create the new commit
+            newParents = newParents
+                .Select(oldParent =>
+                        shaMap.ContainsKey(oldParent.Id)
+                            ? shaMap[oldParent.Id]
+                            : oldParent.Id)
+                .Select(id => repo.Lookup<Commit>(id));
+
             var newCommit = repo.ObjectDatabase.CreateCommit(newHeader.Message, newHeader.Author,
                                                              newHeader.Committer, newTree,
                                                              newParents);