Make RetrieveStatus() reload on-disk index beforehand

LibGit2Sharp.Tests/IndexFixture.cs

@@ -244,5 +244,39 @@ public void StagingAFileWhenTheIndexIsLockedThrowsALockedFileException()
                 Assert.Throws<LockedFileException>(() => repo.Index.Stage("newfile"));
             }
         }
+
+        [Fact]
+        public void CanCopeWithExternalChangesToTheIndex()
+        {
+            SelfCleaningDirectory scd = BuildSelfCleaningDirectory();
+
+            Touch(scd.DirectoryPath, "a.txt", "a\n");
+            Touch(scd.DirectoryPath, "b.txt", "b\n");
+
+            string path = Repository.Init(scd.DirectoryPath);
+
+            using (var repoWrite = new Repository(path))
+            using (var repoRead = new Repository(path))
+            {
+                var writeStatus = repoWrite.Index.RetrieveStatus();
+                Assert.True(writeStatus.IsDirty);
+                Assert.Equal(0, repoWrite.Index.Count);
+
+                var readStatus = repoRead.Index.RetrieveStatus();
+                Assert.True(readStatus.IsDirty);
+                Assert.Equal(0, repoRead.Index.Count);
+
+                repoWrite.Index.Stage("*");
+                repoWrite.Commit("message", Constants.Signature, Constants.Signature);
+
+                writeStatus = repoWrite.Index.RetrieveStatus();
+                Assert.False(writeStatus.IsDirty);
+                Assert.Equal(2, repoWrite.Index.Count);
+
+                readStatus = repoRead.Index.RetrieveStatus();
+                Assert.False(readStatus.IsDirty);
+                Assert.Equal(2, repoRead.Index.Count);
+            }
+        }
     }
 }

LibGit2Sharp/Core/NativeMethods.cs

@@ -492,6 +492,9 @@ internal static extern int git_index_open(
             out IndexSafeHandle index,
             [MarshalAs(UnmanagedType.CustomMarshaler, MarshalCookie = UniqueId.UniqueIdentifier, MarshalTypeRef = typeof(FilePathMarshaler))] FilePath indexpath);
 
+        [DllImport(libgit2)]
+        internal static extern int git_index_read(IndexSafeHandle index);
+
         [DllImport(libgit2)]
         internal static extern int git_index_remove_bypath(
             IndexSafeHandle index,

LibGit2Sharp/Core/Proxy.cs

@@ -776,6 +776,15 @@ public static IndexSafeHandle git_index_open(FilePath indexpath)
             }
         }
 
+        public static void git_index_read(IndexSafeHandle index)
+        {
+            using (ThreadAffinity())
+            {
+                int res = NativeMethods.git_index_read(index);
+                Ensure.ZeroResult(res);
+            }
+        }
+
         public static void git_index_remove_bypath(IndexSafeHandle index, FilePath path)
         {
             using (ThreadAffinity())

LibGit2Sharp/Index.cs

@@ -505,6 +505,7 @@ public virtual FileStatus RetrieveStatus(string filePath)
         /// <returns>A <see cref="RepositoryStatus"/> holding the state of all the files.</returns>
         public virtual RepositoryStatus RetrieveStatus()
         {
+            ReloadFromDisk();
             return new RepositoryStatus(repo);
         }
 
@@ -559,6 +560,11 @@ private void ReplaceIndexEntryWith(TreeEntryChanges treeEntryChanges)
             Marshal.FreeHGlobal(indexEntry.Path);
         }
 
+        internal void ReloadFromDisk()
+        {
+            Proxy.git_index_read(handle);
+        }
+
         private string DebuggerDisplay
         {
             get