Add support for clicking on arrows in the file list to expand/collapse directories (#5365)

### PR Description
This PR adds support for clicking on arrows in the file changes list
view, so that a mouse can be used to expand/collapse directories. This
enhancement was raised here as issue #5088.

pkg/gui/context/base_context.go

@@ -15,7 +15,8 @@ type BaseContext struct {
 
 	keybindingsFns           []types.KeybindingsFn
 	mouseKeybindingsFns      []types.MouseKeybindingsFn
-	onClickFn                func() error
+	onDoubleClickFn          func() error
+	onClickFn                func(opts gocui.ViewMouseBindingOpts) error
 	onClickFocusedMainViewFn onClickFocusedMainViewFn
 	onRenderToMainFn         func()
 	onFocusFns               []onFocusFn
@@ -140,12 +141,22 @@ func (self *BaseContext) ClearAllAttachedControllerFunctions() {
 	self.mouseKeybindingsFns = nil
 	self.onFocusFns = nil
 	self.onFocusLostFns = nil
+	self.onDoubleClickFn = nil
 	self.onClickFn = nil
 	self.onClickFocusedMainViewFn = nil
 	self.onRenderToMainFn = nil
 }
 
-func (self *BaseContext) AddOnClickFn(fn func() error) {
+func (self *BaseContext) AddOnDoubleClickFn(fn func() error) {
+	if fn != nil {
+		if self.onDoubleClickFn != nil {
+			panic("only one controller is allowed to set an onDoubleClickFn")
+		}
+		self.onDoubleClickFn = fn
+	}
+}
+
+func (self *BaseContext) AddOnClickFn(fn func(opts gocui.ViewMouseBindingOpts) error) {
 	if fn != nil {
 		if self.onClickFn != nil {
 			panic("only one controller is allowed to set an onClickFn")
@@ -163,7 +174,11 @@ func (self *BaseContext) AddOnClickFocusedMainViewFn(fn onClickFocusedMainViewFn
 	}
 }
 
-func (self *BaseContext) GetOnClick() func() error {
+func (self *BaseContext) GetOnDoubleClick() func() error {
+	return self.onDoubleClickFn
+}
+
+func (self *BaseContext) GetOnClick() func(opts gocui.ViewMouseBindingOpts) error {
 	return self.onClickFn
 }
 

pkg/gui/context/suggestions_context.go

@@ -89,6 +89,6 @@ func (self *SuggestionsContext) RangeSelectEnabled() bool {
 	return false
 }
 
-func (self *SuggestionsContext) GetOnClick() func() error {
+func (self *SuggestionsContext) GetOnDoubleClick() func() error {
 	return self.State.OnConfirm
 }

pkg/gui/controllers/attach.go

@@ -6,6 +6,7 @@ func AttachControllers(context types.Context, controllers ...types.IController)
 	for _, controller := range controllers {
 		context.AddKeybindingsFn(controller.GetKeybindings)
 		context.AddMouseKeybindingsFn(controller.GetMouseKeybindings)
+		context.AddOnDoubleClickFn(controller.GetOnDoubleClick())
 		context.AddOnClickFn(controller.GetOnClick())
 		context.AddOnClickFocusedMainViewFn(controller.GetOnClickFocusedMainView())
 		context.AddOnRenderToMainFn(controller.GetOnRenderToMain())

pkg/gui/controllers/base_controller.go

@@ -15,7 +15,7 @@ func (self *baseController) GetMouseKeybindings(opts types.KeybindingsOpts) []*g
 	return nil
 }
 
-func (self *baseController) GetOnClick() func() error {
+func (self *baseController) GetOnDoubleClick() func() error {
 	return nil
 }
 
@@ -23,6 +23,10 @@ func (self *baseController) GetOnClickFocusedMainView() func(mainViewName string
 	return nil
 }
 
+func (self *baseController) GetOnClick() func(opts gocui.ViewMouseBindingOpts) error {
+	return nil
+}
+
 func (self *baseController) GetOnRenderToMain() func() {
 	return nil
 }

pkg/gui/controllers/commits_files_controller.go

@@ -142,6 +142,30 @@ func (self *CommitFilesController) context() *context.CommitFilesContext {
 	return self.c.Contexts().CommitFiles
 }
 
+func (self *CommitFilesController) GetOnClick() func(opts gocui.ViewMouseBindingOpts) error {
+	return func(opts gocui.ViewMouseBindingOpts) error {
+		clickedIdx := self.context().GetSelectedLineIdx()
+		node := self.context().CommitFileTreeViewModel.Get(clickedIdx)
+		if node == nil || node.File != nil {
+			return nil
+		}
+
+		// The arrow is at column visualDepth*2 (after indentation of 2 spaces per level).
+		// Only treat clicks on the arrow and the trailing space as arrow clicks.
+		visualDepth := self.context().CommitFileTreeViewModel.GetVisualDepth(clickedIdx)
+		arrowStartCol := visualDepth * 2
+		arrowEndCol := arrowStartCol + 1
+		if opts.X < arrowStartCol || opts.X > arrowEndCol {
+			return nil
+		}
+
+		self.context().CommitFileTreeViewModel.ToggleCollapsed(node.GetInternalPath())
+		self.c.PostRefreshUpdate(self.context())
+
+		return nil
+	}
+}
+
 func (self *CommitFilesController) GetOnRenderToMain() func() {
 	return func() {
 		node := self.context().GetSelected()

pkg/gui/controllers/files_controller.go

@@ -229,6 +229,30 @@ func (self *FilesController) GetMouseKeybindings(opts types.KeybindingsOpts) []*
 	}
 }
 
+func (self *FilesController) GetOnClick() func(opts gocui.ViewMouseBindingOpts) error {
+	return func(opts gocui.ViewMouseBindingOpts) error {
+		clickedIdx := self.context().GetSelectedLineIdx()
+		node := self.context().FileTreeViewModel.Get(clickedIdx)
+		if node == nil || node.File != nil {
+			return nil
+		}
+
+		// The arrow is at column visualDepth*2 (after indentation of 2 spaces per level).
+		// Only treat clicks on the arrow and the trailing space as arrow clicks.
+		visualDepth := self.context().FileTreeViewModel.GetVisualDepth(clickedIdx)
+		arrowStartCol := visualDepth * 2
+		arrowEndCol := arrowStartCol + 1
+		if opts.X < arrowStartCol || opts.X > arrowEndCol {
+			return nil
+		}
+
+		self.context().FileTreeViewModel.ToggleCollapsed(node.GetInternalPath())
+		self.c.PostRefreshUpdate(self.context())
+
+		return nil
+	}
+}
+
 func (self *FilesController) GetOnRenderToMain() func() {
 	return func() {
 		self.c.Helpers().Diff.WithDiffModeCheck(func() {
@@ -329,7 +353,7 @@ func (self *FilesController) GetOnRenderToMain() func() {
 	}
 }
 
-func (self *FilesController) GetOnClick() func() error {
+func (self *FilesController) GetOnDoubleClick() func() error {
 	return self.withItemGraceful(func(node *filetree.FileNode) error {
 		return self.press([]*filetree.FileNode{node})
 	})

pkg/gui/controllers/list_controller.go

@@ -243,10 +243,17 @@ func (self *ListController) HandleClick(opts gocui.ViewMouseBindingOpts) error {
 
 	self.context.GetList().SetSelection(newSelectedLineIdx)
 
-	if opts.IsDoubleClick && alreadyFocused && self.context.GetOnClick() != nil {
-		return self.context.GetOnClick()()
+	if opts.IsDoubleClick && alreadyFocused && self.context.GetOnDoubleClick() != nil {
+		return self.context.GetOnDoubleClick()()
 	}
+
 	self.context.HandleFocus(types.OnFocusOpts{})
+
+	// Let view-specific controllers do additional click handling
+	if self.context.GetOnClick() != nil {
+		return self.context.GetOnClick()(opts)
+	}
+
 	return nil
 }
 

pkg/gui/controllers/menu_controller.go

@@ -55,7 +55,7 @@ func (self *MenuController) GetKeybindings(opts types.KeybindingsOpts) []*types.
 	return bindings
 }
 
-func (self *MenuController) GetOnClick() func() error {
+func (self *MenuController) GetOnDoubleClick() func() error {
 	return self.withItemGraceful(self.press)
 }
 

pkg/gui/controllers/remotes_controller.go

@@ -120,7 +120,7 @@ func (self *RemotesController) GetOnRenderToMain() func() {
 	}
 }
 
-func (self *RemotesController) GetOnClick() func() error {
+func (self *RemotesController) GetOnDoubleClick() func() error {
 	return self.withItemGraceful(self.enter)
 }
 

pkg/gui/controllers/submodules_controller.go

@@ -102,7 +102,7 @@ func (self *SubmodulesController) GetKeybindings(opts types.KeybindingsOpts) []*
 	}
 }
 
-func (self *SubmodulesController) GetOnClick() func() error {
+func (self *SubmodulesController) GetOnDoubleClick() func() error {
 	return self.withItemGraceful(self.enter)
 }
 

pkg/gui/controllers/switch_to_diff_files_controller.go

@@ -54,7 +54,7 @@ func (self *SwitchToDiffFilesController) Context() types.Context {
 	return self.context
 }
 
-func (self *SwitchToDiffFilesController) GetOnClick() func() error {
+func (self *SwitchToDiffFilesController) GetOnDoubleClick() func() error {
 	return func() error {
 		if self.canEnter() == nil {
 			return self.enter()

pkg/gui/controllers/switch_to_sub_commits_controller.go

@@ -55,7 +55,7 @@ func (self *SwitchToSubCommitsController) GetKeybindings(opts types.KeybindingsO
 	return bindings
 }
 
-func (self *SwitchToSubCommitsController) GetOnClick() func() error {
+func (self *SwitchToSubCommitsController) GetOnDoubleClick() func() error {
 	return self.viewCommits
 }
 

pkg/gui/controllers/worktrees_controller.go

@@ -133,7 +133,7 @@ func (self *WorktreesController) remove(worktree *models.Worktree) error {
 	return self.c.Helpers().Worktree.Remove(worktree, false)
 }
 
-func (self *WorktreesController) GetOnClick() func() error {
+func (self *WorktreesController) GetOnDoubleClick() func() error {
 	return self.withItemGraceful(self.enter)
 }
 

pkg/gui/filetree/commit_file_tree.go

@@ -151,6 +151,10 @@ func (self *CommitFileTree) GetFile(path string) *models.CommitFile {
 	return nil
 }
 
+func (self *CommitFileTree) GetVisualDepth(index int) int {
+	return self.tree.GetVisualDepthAtIndex(index+1, self.collapsedPaths) // +1 to skip root
+}
+
 func (self *CommitFileTree) InTreeMode() bool {
 	return self.showTree
 }

pkg/gui/filetree/file_tree.go

@@ -34,6 +34,7 @@ type ITree[T any] interface {
 	CollapsedPaths() *CollapsedPaths
 	CollapseAll()
 	ExpandAll()
+	GetVisualDepth(index int) int
 }
 
 type IFileTree interface {
@@ -221,6 +222,10 @@ func (self *FileTree) CollapsedPaths() *CollapsedPaths {
 	return self.collapsedPaths
 }
 
+func (self *FileTree) GetVisualDepth(index int) int {
+	return self.tree.GetVisualDepthAtIndex(index+1, self.collapsedPaths) // +1 to skip root
+}
+
 func (self *FileTree) GetStatusFilter() FileTreeDisplayFilter {
 	return self.filter
 }

pkg/gui/filetree/node.go

@@ -202,29 +202,43 @@ func (self *Node[T]) GetNodeAtIndex(index int, collapsedPaths *CollapsedPaths) *
 		return nil
 	}
 
-	node, _ := self.getNodeAtIndexAux(index, collapsedPaths)
+	node, _, _ := self.getNodeAtIndexAux(index, collapsedPaths, -1)
 
 	return node
 }
 
-func (self *Node[T]) getNodeAtIndexAux(index int, collapsedPaths *CollapsedPaths) (*Node[T], int) {
+// GetVisualDepthAtIndex returns the visual depth (indentation level) of the
+// node at the given flat index. Visual depth differs from tree depth because
+// compressed nodes (e.g. "a/b/") count as a single visual level.
+// Returns -1 if the index is out of range.
+func (self *Node[T]) GetVisualDepthAtIndex(index int, collapsedPaths *CollapsedPaths) int {
+	if self == nil {
+		return -1
+	}
+
+	_, _, depth := self.getNodeAtIndexAux(index, collapsedPaths, -1)
+
+	return depth
+}
+
+func (self *Node[T]) getNodeAtIndexAux(index int, collapsedPaths *CollapsedPaths, visualDepth int) (*Node[T], int, int) {
 	offset := 1
 
 	if index == 0 {
-		return self, offset
+		return self, offset, visualDepth
 	}
 
 	if !collapsedPaths.IsCollapsed(self.path) {
 		for _, child := range self.Children {
-			foundNode, offsetChange := child.getNodeAtIndexAux(index-offset, collapsedPaths)
+			foundNode, offsetChange, depth := child.getNodeAtIndexAux(index-offset, collapsedPaths, visualDepth+1)
 			offset += offsetChange
 			if foundNode != nil {
-				return foundNode, offset
+				return foundNode, offset, depth
 			}
 		}
 	}
 
-	return nil, offset
+	return nil, offset, -1
 }
 
 func (self *Node[T]) GetIndexForPath(path string, collapsedPaths *CollapsedPaths) (int, bool) {

pkg/gui/filetree/node_test.go

@@ -0,0 +1,134 @@
+package filetree
+
+import (
+	"testing"
+
+	"github.com/jesseduffield/lazygit/pkg/commands/models"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGetVisualDepthAtIndex(t *testing.T) {
+	scenarios := []struct {
+		name           string
+		files          []*models.File
+		showRootItem   bool
+		collapsedPaths []string
+		expectedDepths []int // one per visible node, skipping root
+	}{
+		{
+			name: "flat files with root item",
+			files: []*models.File{
+				{Path: "a"},
+				{Path: "b"},
+			},
+			showRootItem: true,
+			// Displayed as:
+			//   index 0: ▼ /         (depth 0, the "." root dir)
+			//   index 1:   a          (depth 1)
+			//   index 2:   b          (depth 1)
+			expectedDepths: []int{0, 1, 1},
+		},
+		{
+			name: "flat files without root item",
+			files: []*models.File{
+				{Path: "a"},
+				{Path: "b"},
+			},
+			showRootItem: false,
+			// Displayed as:
+			//   index 0: a            (depth 0)
+			//   index 1: b            (depth 0)
+			expectedDepths: []int{0, 0},
+		},
+		{
+			name: "nested directories with root item",
+			files: []*models.File{
+				{Path: "dir/a"},
+				{Path: "dir/b"},
+				{Path: "c"},
+			},
+			showRootItem: true,
+			// Displayed as:
+			//   index 0: ▼ /         (depth 0)
+			//   index 1:   ▼ dir     (depth 1)
+			//   index 2:     a        (depth 2)
+			//   index 3:     b        (depth 2)
+			//   index 4:   c          (depth 1)
+			expectedDepths: []int{0, 1, 2, 2, 1},
+		},
+		{
+			name: "compressed paths with root item",
+			files: []*models.File{
+				{Path: "dir1/dir3/a"},
+				{Path: "dir2/dir4/b"},
+			},
+			showRootItem: true,
+			// Tree compresses dir1/dir3 and dir2/dir4 into single nodes.
+			// Displayed as:
+			//   index 0: ▼ /            (depth 0)
+			//   index 1:   ▼ dir1/dir3  (depth 1, compressed)
+			//   index 2:     a           (depth 2)
+			//   index 3:   ▼ dir2/dir4  (depth 1, compressed)
+			//   index 4:     b           (depth 2)
+			expectedDepths: []int{0, 1, 2, 1, 2},
+		},
+		{
+			name: "compressed paths without root item",
+			files: []*models.File{
+				{Path: "dir1/dir3/a"},
+				{Path: "dir2/dir4/b"},
+			},
+			showRootItem: false,
+			// Displayed as:
+			//   index 0: ▼ dir1/dir3  (depth 0, compressed)
+			//   index 1:   a           (depth 1)
+			//   index 2: ▼ dir2/dir4  (depth 0, compressed)
+			//   index 3:   b           (depth 1)
+			expectedDepths: []int{0, 1, 0, 1},
+		},
+		{
+			name: "collapsed directory hides children",
+			files: []*models.File{
+				{Path: "dir/a"},
+				{Path: "dir/b"},
+				{Path: "c"},
+			},
+			showRootItem:   true,
+			collapsedPaths: []string{"./dir"},
+			// Displayed as:
+			//   index 0: ▼ /         (depth 0)
+			//   index 1:   ▶ dir     (depth 1, collapsed)
+			//   index 2:   c          (depth 1)
+			expectedDepths: []int{0, 1, 1},
+		},
+		{
+			name: "out of range returns -1",
+			files: []*models.File{
+				{Path: "a"},
+			},
+			showRootItem:   false,
+			expectedDepths: []int{0},
+		},
+	}
+
+	for _, s := range scenarios {
+		t.Run(s.name, func(t *testing.T) {
+			tree := BuildTreeFromFiles(s.files, s.showRootItem)
+			collapsedPaths := NewCollapsedPaths()
+			for _, p := range s.collapsedPaths {
+				collapsedPaths.Collapse(p)
+			}
+
+			for i, expectedDepth := range s.expectedDepths {
+				// +1 to skip the invisible root node, matching what FileTree.GetVisualDepth does
+				actualDepth := tree.GetVisualDepthAtIndex(i+1, collapsedPaths)
+				assert.Equal(t, expectedDepth, actualDepth,
+					"index %d: expected depth %d, got %d", i, expectedDepth, actualDepth)
+			}
+
+			// Verify out-of-range returns -1
+			outOfRange := tree.GetVisualDepthAtIndex(len(s.expectedDepths)+1, collapsedPaths)
+			assert.Equal(t, -1, outOfRange, "out of range index should return -1")
+		})
+	}
+}

pkg/gui/types/context.go

@@ -91,13 +91,16 @@ type IBaseContext interface {
 	AddMouseKeybindingsFn(MouseKeybindingsFn)
 	ClearAllAttachedControllerFunctions()
 
-	// This is a bit of a hack at the moment: we currently only set an onclick function so that
-	// our list controller can come along and wrap it in a list-specific click handler.
+	// This is a bit of a hack at the moment: we currently only set an onDoubleClick function so
+	// that the generic ListController can be specialized by view-specific controllers.
 	// We'll need to think of a better way to do this.
-	AddOnClickFn(func() error)
+	AddOnDoubleClickFn(func() error)
 	// Likewise for the focused main view: we need this to communicate between a
 	// side panel controller and the focused main view controller.
 	AddOnClickFocusedMainViewFn(func(mainViewName string, clickedLineIdx int) error)
+	// Adding on to the above, this is so that a list-specific handler can register
+	// a hook for doing additional click handling
+	AddOnClickFn(func(opts gocui.ViewMouseBindingOpts) error)
 
 	AddOnRenderToMainFn(func())
 	AddOnFocusFn(func(OnFocusOpts))
@@ -246,7 +249,19 @@ type (
 type HasKeybindings interface {
 	GetKeybindings(opts KeybindingsOpts) []*Binding
 	GetMouseKeybindings(opts KeybindingsOpts) []*gocui.ViewMouseBinding
-	GetOnClick() func() error
+
+	// Implement this to get called when there's a double-click on the view. Only supported by list
+	// views currently. Will be called after the double-clicked list entry has been selected.
+	GetOnDoubleClick() func() error
+
+	// Implement this to get called for any non-double-click in the view. Only supported by list
+	// views currently. Will be called after the clicked list entry has been selected, and
+	// HandleFocus has already been called (so the main view is up to date). Should return nil if it
+	// decides not to do anything with the click.
+	GetOnClick() func(opts gocui.ViewMouseBindingOpts) error
+
+	// Implement this in a side-panel controller to get called when there's a click in the main view
+	// that belongs to your panel while the main view is already focused.
 	GetOnClickFocusedMainView() func(mainViewName string, clickedLineIdx int) error
 }
 

pkg/integration/tests/file/click_arrow_to_collapse.go

@@ -0,0 +1,86 @@
+package file
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var ClickArrowToCollapse = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Click the arrow on a directory to collapse/expand it",
+	ExtraCmdArgs: []string{},
+	Skip:         false,
+	SetupConfig:  func(config *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.CreateDir("dir")
+		shell.CreateFile("dir/file-one", "original content\n")
+		shell.CreateDir("dir2")
+		shell.CreateFile("dir2/file-two", "original content\n")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Files().
+			IsFocused().
+			Lines(
+				Equals("▼ /").IsSelected(),
+				Equals("  ▼ dir"),
+				Equals("    ?? file-one"),
+				Equals("  ▼ dir2"),
+				Equals("    ?? file-two"),
+			)
+
+		// Click the arrow on "dir" (row 1, column 2) to collapse it
+		t.Views().Files().
+			Click(2, 1).
+			Lines(
+				Equals("▼ /"),
+				Equals("  ▶ dir").IsSelected(),
+				Equals("  ▼ dir2"),
+				Equals("    ?? file-two"),
+			)
+
+		// Click one to the right of the arrow on "dir2" (row 2, column 3) to collapse it
+		// Arrow + space after should register a collapse toggle
+		t.Views().Files().
+			Click(3, 2).
+			Lines(
+				Equals("▼ /"),
+				Equals("  ▶ dir"),
+				Equals("  ▶ dir2").IsSelected(),
+			)
+
+		// Click one to the left of the arrow on "dir2" (row 2, column 1)
+		// Space before arrow should not register a collapse toggle
+		t.Views().Files().
+			Click(1, 2).
+			Lines(
+				Equals("▼ /"),
+				Equals("  ▶ dir"),
+				Equals("  ▶ dir2").IsSelected(),
+			)
+
+		// Clicking on the file/directory name "dir" should change selected but not toggle collapse
+		t.Views().Files().
+			Click(5, 1).
+			Lines(
+				Equals("▼ /"),
+				Equals("  ▶ dir").IsSelected(),
+				Equals("  ▶ dir2"),
+			)
+
+		// Click the arrow again to expand it
+		t.Views().Files().
+			Click(2, 1).
+			Lines(
+				Equals("▼ /"),
+				Equals("  ▼ dir").IsSelected(),
+				Equals("    ?? file-one"),
+				Equals("  ▶ dir2"),
+			)
+
+		// Click the arrow on the root "/" (row 0, column 0) to collapse everything
+		t.Views().Files().
+			Click(0, 0).
+			Lines(
+				Equals("▶ /").IsSelected(),
+			)
+	},
+})

pkg/integration/tests/test_list.go

@@ -210,6 +210,7 @@ var tests = []*components.IntegrationTest{
 	diff.DiffNonStickyRange,
 	diff.IgnoreWhitespace,
 	diff.RenameSimilarityThresholdChange,
+	file.ClickArrowToCollapse,
 	file.CollapseExpand,
 	file.CopyMenu,
 	file.DirWithUntrackedFile,