Feature: Diff List sorting options

Defaults to file path sorting as it was pre 3.0 and was changed by accident.
Context menu in a diff list will provide you with the ability to select the sorting method. Changing one will affect all others and is persisted across processes.
Added ImageIndexListSorter to sort by change type according to the image they have then by file path.
Added GitItemStatusFileExtensionComparer to sort by the file extension then by the file path.

GitCommands/DiffListSortService.cs

@@ -0,0 +1,46 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace GitCommands
+{
+    public class DiffListSortService : IDiffListSortService
+    {
+        private static readonly Lazy<DiffListSortService> _lazyDiffListSorting = new Lazy<DiffListSortService>(() => new DiffListSortService());
+        public static DiffListSortService Instance => _lazyDiffListSorting.Value;
+        private DiffListSortType _diffListSorting;
+        public event EventHandler DiffListSortingChanged;
+
+        public DiffListSortType DiffListSorting
+        {
+            get { return _diffListSorting; }
+            set
+            {
+                var previous = _diffListSorting;
+                if (previous != value)
+                {
+                    _diffListSorting = value;
+                    AppSettings.DiffListSorting = value;
+                    OnDiffListSortingChanged();
+                }
+            }
+        }
+
+        public DiffListSortService()
+        {
+            DiffListSorting = GetSettingValueOrDefault();
+        }
+
+        private DiffListSortType GetSettingValueOrDefault()
+        {
+            return AppSettings.DiffListSorting;
+        }
+
+        protected void OnDiffListSortingChanged()
+        {
+            DiffListSortingChanged?.Invoke(this, EventArgs.Empty);
+        }
+    }
+}

GitCommands/Git/GitItemStatusFileExtensionComparer.cs

@@ -0,0 +1,55 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace GitCommands.Git
+{
+    /// <summary>
+    /// Compares the file extension of <see cref="GitItemStatus.Name"/> and then by <see cref="GitItemStatus.CompareTo(GitItemStatus)"/>.
+    /// </summary>
+    public class GitItemStatusFileExtensionComparer : Comparer<GitItemStatus>
+    {
+        public override int Compare(GitItemStatus x, GitItemStatus y)
+        {
+            if (ReferenceEquals(x, y))
+            {
+                return 0;
+            }
+
+            if (x == null)
+            {
+                return -1;
+            }
+
+            if (y == null)
+            {
+                return 1;
+            }
+
+            var lhsPath = GetPrimarySortingPath(x);
+            var rhsPath = GetPrimarySortingPath(y);
+            var lhsExt = Path.GetExtension(lhsPath);
+            var rhsExt = Path.GetExtension(rhsPath);
+
+            var comparisonResult = StringComparer.InvariantCulture.Compare(lhsExt, rhsExt);
+            if (comparisonResult == 0)
+            {
+                // originally used Comparer<GitItemStatus>.Default.Compare(x, y) but this would
+                // produce incorrect results when the oldName was the only available path on an item.
+                return StringComparer.InvariantCulture.Compare(lhsPath, rhsPath);
+            }
+
+            return comparisonResult;
+        }
+
+        private static string GetPrimarySortingPath(GitItemStatus itemStatus)
+        {
+            return !string.IsNullOrEmpty(itemStatus.Name)
+                ? itemStatus.Name
+                : itemStatus.OldName;
+        }
+    }
+}

GitCommands/GitCommands.csproj

@@ -72,6 +72,7 @@
     <Compile Include="DateTimeExtensions.cs" />
     <Compile Include="DateTimeUtils.cs" />
     <Compile Include="DeconstructionExtensions.cs" />
+    <Compile Include="DiffListSortService.cs" />
     <Compile Include="EnvironmentAbstraction.cs" />
     <Compile Include="EnvironmentPathsProvider.cs" />
     <Compile Include="ExceptionUtils.cs" />
@@ -101,6 +102,7 @@
     <Compile Include="Git\GitBranchNameOptions.cs" />
     <Compile Include="Git\Extensions\GitRevisionExtensions.cs" />
     <Compile Include="Git\Executable.cs" />
+    <Compile Include="Git\GitItemStatusFileExtensionComparer.cs" />
     <Compile Include="Git\GitModuleEventArgs.cs" />
     <Compile Include="Git\GitRevisionTester.cs" />
     <Compile Include="Git\GitRefName.cs" />
@@ -114,6 +116,7 @@
     <Compile Include="Git\Tag\GitTagController.cs" />
     <Compile Include="Git\Tag\TagOperation.cs" />
     <Compile Include="Git\Tag\TagOperationExtensions.cs" />
+    <Compile Include="IDiffListSortService.cs" />
     <Compile Include="Plink.cs" />
     <Compile Include="Remotes\GitRemoteManager.cs" />
     <Compile Include="Remotes\RepoNameExtractor.cs" />

GitCommands/IDiffListSortService.cs

@@ -0,0 +1,52 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reactive.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace GitCommands
+{
+    public enum DiffListSortType
+    {
+        /// <summary>
+        /// Sorts by file path alphanumerically
+        /// </summary>
+        FilePath,
+
+        /// <summary>
+        /// Sorts by file extension then by path
+        /// </summary>
+        FileExtension,
+
+        /// <summary>
+        /// Sorts by git change type. Addition, Deletions, edits, etc. then by path
+        /// </summary>
+        FileStatus
+    }
+
+    public interface IDiffListSortService
+    {
+        DiffListSortType DiffListSorting { get; set; }
+
+        event EventHandler DiffListSortingChanged;
+    }
+
+    public static class DiffListSortServiceExtensions
+    {
+        /// <summary>
+        /// Provides the <see cref="IDiffListSortService.DiffListSorting"/> immediately and then an element for each <see cref="IDiffListSortService.DiffListSortingChanged"/>.
+        /// </summary>
+        /// <param name="diffListSortService">The diff list service</param>
+        /// <returns>A hot stream with one immediate cold element.</returns>
+        public static IObservable<DiffListSortType> CurrentAndFutureSorting(this IDiffListSortService diffListSortService)
+        {
+            return Observable.Return(diffListSortService.DiffListSorting)
+                .Concat(Observable.FromEventPattern(
+                    h => diffListSortService.DiffListSortingChanged += h,
+                    h => diffListSortService.DiffListSortingChanged -= h)
+                    .Select(_ => diffListSortService.DiffListSorting))
+                .DistinctUntilChanged();
+        }
+    }
+}

GitCommands/Settings/AppSettings.cs

@@ -1546,6 +1546,12 @@ public static bool UseConsoleEmulatorForCommands
             set => SetBool("UseConsoleEmulatorForCommands", value);
         }
 
+        public static DiffListSortType DiffListSorting
+        {
+            get => GetEnum("DiffListSortType", DiffListSortType.FilePath);
+            set => SetEnum("DiffListSortType", value);
+        }
+
         public static string GetGitExtensionsFullPath()
         {
             return Application.ExecutablePath;

GitUI/GitUI.csproj

@@ -515,6 +515,9 @@
     <Compile Include="UserControls\RevisionGrid\RevisionGridRefRenderer.cs" />
     <Compile Include="UserControls\RevisionGrid\SuperProjectInfo.cs" />
     <Compile Include="UserControls\RevisionGrid\VisibleRowRange.cs" />
+    <Compile Include="UserControls\SortDiffListContextMenuItem.cs">
+      <SubType>Component</SubType>
+    </Compile>
     <Compile Include="UserControls\TextEventArgs.cs" />
     <Compile Include="UserControls\RepoStateVisualiser.cs" />
     <Compile Include="CommandsDialogs\BrowseDialog\GitStatusMonitor.cs" />

GitUI/Properties/Images.resx

@@ -799,4 +799,7 @@
   <data name="DocumentTree" type="System.Resources.ResXFileRef, System.Windows.Forms">
     <value>..\Resources\Icons\DocumentTree.png;System.Drawing.Bitmap, System.Drawing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a</value>
   </data>
+  <data name="SortBy" type="System.Resources.ResXFileRef, System.Windows.Forms">
+    <value>..\Resources\Icons\SortBy.png;System.Drawing.Bitmap, System.Drawing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a</value>
+  </data>
 </root>