Teach Checkout() to append to the reflog

When no user information exists in the configuration, a dummy signature
is created to value the reflog entry.

1 files changed, 29 insertions, 0 deletions

diff --git a/LibGit2Sharp/Repository.cs b/LibGit2Sharp/Repository.cs
index 39cd5f1b..a14a61e3 100644
--- a/LibGit2Sharp/Repository.cs
+++ b/LibGit2Sharp/Repository.cs
@@ -586,11 +586,17 @@ namespace LibGit2Sharp
                 return Checkout(branch, checkoutOptions, onCheckoutProgress);
             }
 
+            var previousHeadName = Info.IsHeadDetached ? Head.Tip.Sha : Head.Name;
+
             Commit commit = LookupCommit(committishOrBranchSpec);
             CheckoutTree(commit.Tree, checkoutOptions, onCheckoutProgress);
 
             // Update HEAD.
             Refs.UpdateTarget("HEAD", commit.Id.Sha);
+            if (committishOrBranchSpec != "HEAD")
+            {
+                LogCheckout(previousHeadName, commit.Id, committishOrBranchSpec);
+            }
 
             return Head;
         }
@@ -633,6 +639,9 @@ namespace LibGit2Sharp
                     "The tip of branch '{0}' is null. There's nothing to checkout.", branch.Name));
             }
 
+            var branchIsCurrentRepositoryHead = branch.IsCurrentRepositoryHead;
+            var previousHeadName = Info.IsHeadDetached ? Head.Tip.Sha : Head.Name;
+
             CheckoutTree(branch.Tip.Tree, checkoutOptions, onCheckoutProgress);
 
             // Update HEAD.
@@ -647,9 +656,29 @@ namespace LibGit2Sharp
                 Refs.UpdateTarget("HEAD", branch.Tip.Id.Sha);
             }
 
+            if (!branchIsCurrentRepositoryHead)
+            {
+                LogCheckout(previousHeadName, branch);
+            }
+
             return Head;
         }
 
+        private void LogCheckout(string previousHeadName, Branch newHead)
+        {
+            LogCheckout(previousHeadName, newHead.Tip.Id, newHead.Name);
+        }
+
+        private void LogCheckout(string previousHeadName, ObjectId newHeadTip, string newHeadSpec)
+        {
+            // Compute reflog message
+            string reflogMessage = string.Format("checkout: moving from {0} to {1}", previousHeadName, newHeadSpec);
+
+            // Log checkout
+            Signature author = Config.BuildSignatureFromGlobalConfiguration(DateTimeOffset.Now, false);
+            Refs.Log(Refs.Head).Append(newHeadTip, author, reflogMessage);
+        }
+
         /// <summary>
         ///   Internal implementation of Checkout that expects the ID of the checkout target
         ///   to already be in the form of a canonical branch name or a commit ID.