feature: drag and drop branches around in the branch tree

src/Resources/Locales/en_US.axaml

@@ -58,7 +58,9 @@
   <x:String x:Key="Text.Blame.Tips" xml:space="preserve">Holding Ctrl (on Windows/Linux) or ⌘ (on macOS) when clicking commit SHA will rebuild blame data based on that revision.</x:String>
   <x:String x:Key="Text.Blame.TypeNotSupported" xml:space="preserve">BLAME ON THIS FILE IS NOT SUPPORTED!!!</x:String>
   <x:String x:Key="Text.BranchCM.Checkout" xml:space="preserve">Checkout ${0}$...</x:String>
+  <x:String x:Key="Text.BranchCM.CheckoutAndMerge" xml:space="preserve">Checkout ${1}$ and merge ${0}$ into it...</x:String>
   <x:String x:Key="Text.BranchCM.CheckoutAsWorktree" xml:space="preserve">Checkout ${0}$ as worktree...</x:String>
+  <x:String x:Key="Text.BranchCM.CompareBranches" xml:space="preserve">Compare ${0}$ with ${1}$</x:String>
   <x:String x:Key="Text.BranchCM.CompareTwo" xml:space="preserve">Compare selected 2 branches</x:String>
   <x:String x:Key="Text.BranchCM.CompareWith" xml:space="preserve">Compare with...</x:String>
   <x:String x:Key="Text.BranchCM.CompareWithHead" xml:space="preserve">Compare with HEAD</x:String>
@@ -71,6 +73,7 @@
   <x:String x:Key="Text.BranchCM.DeleteMultiBranches" xml:space="preserve">Delete selected {0} branches...</x:String>
   <x:String x:Key="Text.BranchCM.EditDescription" xml:space="preserve">Edit description for ${0}$...</x:String>
   <x:String x:Key="Text.BranchCM.FastForward" xml:space="preserve">Fast-Forward to ${0}$</x:String>
+  <x:String x:Key="Text.BranchCM.FastForwardBranch" xml:space="preserve">Fast-Forward ${0}$ to ${1}$</x:String>
   <x:String x:Key="Text.BranchCM.FetchInto" xml:space="preserve">Fetch ${0}$ into ${1}$</x:String>
   <x:String x:Key="Text.BranchCM.Finish" xml:space="preserve">Git Flow - Finish ${0}$...</x:String>
   <x:String x:Key="Text.BranchCM.InteractiveRebase.Manually" xml:space="preserve">Interactively Rebase ${0}$ on ${1}$</x:String>
@@ -629,6 +632,11 @@
   <x:String x:Key="Text.MergeMultiple.CommitChanges" xml:space="preserve">Commit all changes</x:String>
   <x:String x:Key="Text.MergeMultiple.Strategy" xml:space="preserve">Strategy:</x:String>
   <x:String x:Key="Text.MergeMultiple.Targets" xml:space="preserve">Targets:</x:String>
+  <x:String x:Key="Text.MoveBranches" xml:space="preserve">Move Branches</x:String>
+  <x:String x:Key="Text.MoveBranches.Branches" xml:space="preserve">Branches:</x:String>
+  <x:String x:Key="Text.MoveBranches.Count" xml:space="preserve">{0} items</x:String>
+  <x:String x:Key="Text.MoveBranches.Root" xml:space="preserve">(top level)</x:String>
+  <x:String x:Key="Text.MoveBranches.Target" xml:space="preserve">Move Into:</x:String>
   <x:String x:Key="Text.MoveSubmodule" xml:space="preserve">Move Submodule</x:String>
   <x:String x:Key="Text.MoveSubmodule.MoveTo" xml:space="preserve">Move To:</x:String>
   <x:String x:Key="Text.MoveSubmodule.Submodule" xml:space="preserve">Submodule:</x:String>

src/ViewModels/BranchTreeNode.cs

@@ -34,6 +34,12 @@ public CornerRadius CornerRadius
             set => SetProperty(ref _cornerRadius, value);
         }
 
+        public bool IsDropTarget
+        {
+            get => _isDropTarget;
+            set => SetProperty(ref _isDropTarget, value);
+        }
+
         public bool IsBranch
         {
             get => Backend is Models.Branch;
@@ -56,6 +62,7 @@ public string BranchesCount
 
         private Models.FilterMode _filterMode = Models.FilterMode.None;
         private bool _isExpanded = false;
+        private bool _isDropTarget = false;
         private CornerRadius _cornerRadius = new CornerRadius(4);
 
         public class Builder

src/ViewModels/MoveBranches.cs

@@ -0,0 +1,173 @@
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+namespace SourceGit.ViewModels
+{
+    public class MoveBranches : Popup
+    {
+        public const string LocalPrefix = "refs/heads/";
+
+        public string Target
+        {
+            get;
+        }
+
+        public List<string> Preview
+        {
+            get;
+        } = [];
+
+        public string ErrorMessage
+        {
+            get;
+        } = string.Empty;
+
+        public bool HasError
+        {
+            get => !string.IsNullOrEmpty(ErrorMessage);
+        }
+
+        public MoveBranches(Repository repo, IReadOnlyList<string> paths, string targetPrefix)
+        {
+            _repo = repo;
+            Target = string.IsNullOrEmpty(targetPrefix) ? App.Text("MoveBranches.Root") : $"{targetPrefix}/";
+
+            foreach (var path in paths)
+            {
+                if (!path.StartsWith(LocalPrefix, StringComparison.Ordinal))
+                    continue;
+
+                var parent = GetParent(path.Substring(LocalPrefix.Length));
+                if (parent.Equals(targetPrefix, StringComparison.Ordinal))
+                    continue;
+
+                var folderPrefix = $"{path}/";
+                foreach (var branch in repo.Branches)
+                {
+                    if (!branch.IsLocal)
+                        continue;
+
+                    if (branch.FullName.Equals(path, StringComparison.Ordinal) ||
+                        branch.FullName.StartsWith(folderPrefix, StringComparison.Ordinal))
+                    {
+                        var leaf = parent.Length == 0 ? branch.Name : branch.Name.Substring(parent.Length + 1);
+                        var newName = targetPrefix.Length == 0 ? leaf : $"{targetPrefix}/{leaf}";
+                        _moves.Add(new KeyValuePair<Models.Branch, string>(branch, newName));
+                        Preview.Add($"{branch.Name}  →  {newName}");
+                    }
+                }
+            }
+
+            ErrorMessage = Validate();
+        }
+
+        // Whether dropping the given tree node paths on the folder `targetPrefix` ("" for the top level) would
+        // move anything. Folders cannot be dropped into themselves, and items already there are no-ops.
+        public static bool CanDropOnto(IReadOnlyList<string> paths, string targetPrefix)
+        {
+            if (paths.Count == 0)
+                return false;
+
+            var anyMoves = false;
+            foreach (var path in paths)
+            {
+                if (!path.StartsWith(LocalPrefix, StringComparison.Ordinal))
+                    return false;
+
+                var relative = path.Substring(LocalPrefix.Length);
+                if (targetPrefix.Equals(relative, StringComparison.Ordinal) ||
+                    targetPrefix.StartsWith($"{relative}/", StringComparison.Ordinal))
+                    return false;
+
+                if (!GetParent(relative).Equals(targetPrefix, StringComparison.Ordinal))
+                    anyMoves = true;
+            }
+
+            return anyMoves;
+        }
+
+        public override async Task<bool> Sure()
+        {
+            if (HasError)
+            {
+                _repo.SendNotification(ErrorMessage, true);
+                return false;
+            }
+
+            using var lockWatcher = _repo.LockWatcher();
+
+            var log = _repo.CreateLog("Move Branches");
+            Use(log);
+
+            var succ = true;
+            foreach (var (branch, newName) in _moves)
+            {
+                ProgressDescription = $"Rename '{branch.Name}'";
+
+                succ = await new Commands.Branch(_repo.FullPath, branch.Name)
+                    .Use(log)
+                    .RenameAsync(newName);
+
+                if (!succ)
+                    break;
+
+                _repo.RefreshAfterRenameBranch(branch, newName);
+            }
+
+            log.Complete();
+            return succ;
+        }
+
+        private string Validate()
+        {
+            if (_moves.Count == 0)
+                return "Nothing to move!";
+
+            var moving = new HashSet<Models.Branch>();
+            foreach (var (branch, _) in _moves)
+                moving.Add(branch);
+
+            for (var i = 0; i < _moves.Count; i++)
+            {
+                var name = _moves[i].Value;
+                if (!Models.RefName.IsValidBranchName(name))
+                    return $"Bad branch name format: {name}";
+
+                foreach (var other in _repo.Branches)
+                {
+                    if (!other.IsLocal || moving.Contains(other))
+                        continue;
+
+                    if (Conflicts(name, other.Name))
+                        return $"A branch named '{other.Name}' already exists!!!";
+                }
+
+                for (var j = i + 1; j < _moves.Count; j++)
+                {
+                    if (Conflicts(name, _moves[j].Value))
+                        return $"Branches would end up with the same name: {name}";
+                }
+            }
+
+            return string.Empty;
+        }
+
+        // Two branch names cannot coexist when they are equal or one is a "directory" of the other.
+        private static bool Conflicts(string a, string b)
+        {
+            return a.Equals(b, StringComparison.Ordinal) ||
+                a.StartsWith($"{b}/", StringComparison.Ordinal) ||
+                b.StartsWith($"{a}/", StringComparison.Ordinal);
+        }
+
+        private static string GetParent(string relativePath)
+        {
+            var idx = relativePath.LastIndexOf('/');
+            return idx < 0 ? string.Empty : relativePath.Substring(0, idx);
+        }
+
+        private readonly Repository _repo;
+        private readonly List<KeyValuePair<Models.Branch, string>> _moves = [];
+    }
+}

src/Views/BranchTree.axaml

@@ -35,10 +35,26 @@
 
     <ListBox.ItemTemplate>
       <DataTemplate DataType="vm:BranchTreeNode">
-        <Border Background="Transparent"
+        <Border Classes="branch_node"
+                Classes.drop_target="{Binding IsDropTarget}"
                 PointerPressed="OnNodePointerPressed"
+                PointerMoved="OnNodePointerMoved"
+                PointerReleased="OnNodePointerReleased"
+                DragDrop.AllowDrop="True"
+                DragDrop.DragOver="OnNodeDragOver"
+                DragDrop.DragLeave="OnNodeDragLeave"
+                DragDrop.Drop="OnNodeDrop"
                 ToolTip.Tip="{Binding Backend}"
                 ToolTip.Placement="Right">
+          <Border.Styles>
+            <Style Selector="Border.branch_node">
+              <Setter Property="Background" Value="Transparent"/>
+            </Style>
+            <Style Selector="Border.branch_node.drop_target">
+              <Setter Property="Background" Value="{DynamicResource Brush.AccentHovered}"/>
+            </Style>
+          </Border.Styles>
+
           <Border.DataTemplates>
             <DataTemplate DataType="m:Branch">
               <StackPanel Orientation="Vertical">