Support to request a content-only UI refresh

This skips the whole-UI layout calculations, and lets tcell's dirty cell
handling redraw only changed cells.

pkg/gocui/flush_test.go

@@ -0,0 +1,202 @@
+package gocui
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func newTestGui(t *testing.T) *Gui {
+	t.Helper()
+	g, err := NewGui(NewGuiOpts{
+		OutputMode: OutputNormal,
+		Headless:   true,
+		Width:      80,
+		Height:     24,
+	})
+	assert.NoError(t, err)
+	t.Cleanup(func() { g.Close() })
+	return g
+}
+
+// setupViews creates a few views and does an initial full flush so all views
+// start in a clean (non-tainted) state.
+func setupViews(t *testing.T, g *Gui) (*View, *View) {
+	t.Helper()
+
+	status, _ := g.SetView("status", 0, 22, 40, 24, 0)
+	status.Frame = false
+	main, _ := g.SetView("main", 0, 0, 80, 22, 0)
+
+	// Initial content
+	status.SetContent("Ready")
+	main.SetContent("hello world")
+
+	// Full flush to draw everything and clear tainted flags
+	assert.NoError(t, g.flush())
+
+	return status, main
+}
+
+// pushContentOnly pushes a content-only event directly to the channel
+// (synchronous, deterministic — unlike Update which spawns a goroutine).
+func pushContentOnly(g *Gui, f func(*Gui) error) {
+	g.userEvents <- userEvent{f: f, task: g.NewTask(), contentOnly: true}
+}
+
+// pushRegular pushes a regular event directly to the channel.
+func pushRegular(g *Gui, f func(*Gui) error) {
+	g.userEvents <- userEvent{f: f, task: g.NewTask(), contentOnly: false}
+}
+
+func TestFlushContentOnly_SkipsUntaintedViews(t *testing.T) {
+	g := newTestGui(t)
+	status, main := setupViews(t, g)
+
+	// After initial flush, both views should be untainted
+	assert.False(t, status.IsTainted(), "status view should not be tainted after flush")
+	assert.False(t, main.IsTainted(), "main view should not be tainted after flush")
+
+	// Modify only the status view
+	status.SetContent("Fetching /")
+
+	assert.True(t, status.IsTainted(), "status view should be tainted after SetContent")
+	assert.False(t, main.IsTainted(), "main view should not be tainted (was not modified)")
+
+	// flushContentOnly should succeed and clear status tainted flag
+	assert.NoError(t, g.flushContentOnly())
+
+	assert.False(t, status.IsTainted(), "status view should not be tainted after flushContentOnly")
+	assert.False(t, main.IsTainted(), "main view should not be tainted after flushContentOnly")
+}
+
+func TestFlushContentOnly_WritesCorrectContent(t *testing.T) {
+	g := newTestGui(t)
+	status, _ := setupViews(t, g)
+
+	status.SetContent("Fetching |")
+	assert.NoError(t, g.flushContentOnly())
+
+	assert.Equal(t, "Fetching |", status.Buffer())
+}
+
+func TestProcessEvent_ContentOnlyEvent_SkipsTaintedCheck(t *testing.T) {
+	g := newTestGui(t)
+	status, main := setupViews(t, g)
+
+	// Send a content-only event that modifies only the status view
+	pushContentOnly(g, func(gui *Gui) error {
+		status.SetContent("Fetching /")
+		return nil
+	})
+
+	assert.NoError(t, g.processEvent())
+
+	// status was modified and drawn → tainted cleared
+	assert.False(t, status.IsTainted(), "status should not be tainted after processEvent with contentOnly")
+	// main was NOT modified → should still be untainted
+	assert.False(t, main.IsTainted(), "main should not be tainted after processEvent with contentOnly")
+}
+
+func TestProcessEvent_RegularEvent_UsesFullFlush(t *testing.T) {
+	g := newTestGui(t)
+	status, _ := setupViews(t, g)
+
+	// Regular event (not content-only) should trigger full flush
+	pushRegular(g, func(gui *Gui) error {
+		status.SetContent("Fetching \\")
+		return nil
+	})
+
+	assert.NoError(t, g.processEvent())
+
+	assert.False(t, status.IsTainted(), "status should not be tainted after full flush")
+}
+
+func TestProcessEvent_MixedBatch_UsesFullFlush(t *testing.T) {
+	g := newTestGui(t)
+	status, main := setupViews(t, g)
+
+	// Queue a content-only event followed by a regular event.
+	// processEvent picks up the first; processRemainingEvents picks up
+	// the second. Since the second is not contentOnly, full flush runs.
+	pushContentOnly(g, func(gui *Gui) error {
+		status.SetContent("Fetching -")
+		return nil
+	})
+	pushRegular(g, func(gui *Gui) error {
+		main.SetContent("updated main")
+		return nil
+	})
+
+	assert.NoError(t, g.processEvent())
+
+	// Both views were modified and should have been drawn by full flush
+	assert.False(t, status.IsTainted(), "status should not be tainted after full flush")
+	assert.False(t, main.IsTainted(), "main should not be tainted after full flush")
+}
+
+func TestProcessEvent_RegularThenContentOnly_UsesFullFlush(t *testing.T) {
+	g := newTestGui(t)
+	status, main := setupViews(t, g)
+
+	// Even if a regular event comes first and the remaining are contentOnly,
+	// the batch must use full flush.
+	pushRegular(g, func(gui *Gui) error {
+		main.SetContent("new main content")
+		return nil
+	})
+	pushContentOnly(g, func(gui *Gui) error {
+		status.SetContent("Fetching |")
+		return nil
+	})
+
+	assert.NoError(t, g.processEvent())
+
+	assert.False(t, status.IsTainted(), "status should not be tainted after full flush")
+	assert.False(t, main.IsTainted(), "main should not be tainted after full flush")
+}
+
+func TestProcessRemainingEvents_AllContentOnly_ReturnsTrue(t *testing.T) {
+	g := newTestGui(t)
+	status, _ := setupViews(t, g)
+
+	pushContentOnly(g, func(gui *Gui) error {
+		status.SetContent("a")
+		return nil
+	})
+	pushContentOnly(g, func(gui *Gui) error {
+		status.SetContent("b")
+		return nil
+	})
+
+	contentOnly, err := g.processRemainingEvents()
+	assert.NoError(t, err)
+	assert.True(t, contentOnly, "should return true when all events are contentOnly")
+}
+
+func TestProcessRemainingEvents_MixedEvents_ReturnsFalse(t *testing.T) {
+	g := newTestGui(t)
+	status, _ := setupViews(t, g)
+
+	pushContentOnly(g, func(gui *Gui) error {
+		status.SetContent("a")
+		return nil
+	})
+	pushRegular(g, func(gui *Gui) error {
+		status.SetContent("b")
+		return nil
+	})
+
+	contentOnly, err := g.processRemainingEvents()
+	assert.NoError(t, err)
+	assert.False(t, contentOnly, "should return false when any event is not contentOnly")
+}
+
+func TestProcessRemainingEvents_EmptyQueue_ReturnsTrue(t *testing.T) {
+	g := newTestGui(t)
+
+	contentOnly, err := g.processRemainingEvents()
+	assert.NoError(t, err)
+	assert.True(t, contentOnly, "should return true when no events are queued")
+}

pkg/gocui/gui.go

@@ -604,6 +604,10 @@ func (g *Gui) SetRenderSearchStatusFunc(renderSearchStatusFunc func(*View, int,
 type userEvent struct {
 	f    func(*Gui) error
 	task Task
+	// Signals that this event only modifies view content (e.g. SetContent).
+	// When all events in a batch are contentOnly, processEvent
+	// can skip the expensive layout() call in flush().
+	contentOnly bool
 }
 
 // Update executes the passed function. This method can be called safely from a
@@ -630,6 +634,12 @@ func (g *Gui) updateAsyncAux(f func(*Gui) error, task Task) {
 	g.userEvents <- userEvent{f: f, task: task}
 }
 
+// Like Update, but signals that the callback only modifies content.
+func (g *Gui) UpdateContentOnly(f func(*Gui) error) {
+	task := g.NewTask()
+	g.userEvents <- userEvent{f: f, task: task, contentOnly: true}
+}
+
 // Calls a function in a goroutine. Handles panics gracefully and tracks
 // number of background tasks.
 // Always use this when you want to spawn a goroutine and you want lazygit to
@@ -743,6 +753,8 @@ func (g *Gui) handleError(err error) error {
 }
 
 func (g *Gui) processEvent() error {
+	contentOnly := false
+
 	select {
 	case ev := <-g.gEvents:
 		task := g.NewTask()
@@ -752,6 +764,7 @@ func (g *Gui) processEvent() error {
 			return err
 		}
 	case ev := <-g.userEvents:
+		contentOnly = ev.contentOnly
 		defer func() { ev.task.Done() }()
 
 		if err := g.handleError(ev.f(g)); err != nil {
@@ -759,32 +772,38 @@ func (g *Gui) processEvent() error {
 		}
 	}
 
-	if err := g.processRemainingEvents(); err != nil {
-		return err
-	}
-	if err := g.flush(); err != nil {
+	remainingContentOnly, err := g.processRemainingEvents()
+	if err != nil {
 		return err
 	}
+	contentOnly = contentOnly && remainingContentOnly
 
-	return nil
+	if contentOnly {
+		return g.flushContentOnly()
+	}
+	return g.flush()
 }
 
 // processRemainingEvents handles the remaining events in the events pool.
-func (g *Gui) processRemainingEvents() error {
+// Returns true if all processed events were content-only.
+func (g *Gui) processRemainingEvents() (bool, error) {
+	contentOnly := true
 	for {
 		select {
 		case ev := <-g.gEvents:
+			contentOnly = false
 			if err := g.handleError(g.handleEvent(&ev)); err != nil {
-				return err
+				return false, err
 			}
 		case ev := <-g.userEvents:
+			contentOnly = ev.contentOnly && contentOnly
 			err := g.handleError(ev.f(g))
 			ev.task.Done()
 			if err != nil {
-				return err
+				return false, err
 			}
 		default:
-			return nil
+			return contentOnly, nil
 		}
 	}
 }
@@ -1169,6 +1188,23 @@ func (g *Gui) ForceRedrawViews(views ...*View) error {
 	return nil
 }
 
+// Redraws only tainted views and skips the layout pass.
+// tcell's cell-level dirty tracking ensures only
+// actually-changed cells are emitted to the terminal.
+func (g *Gui) flushContentOnly() error {
+	for _, v := range g.views {
+		if !v.tainted {
+			continue
+		}
+		if err := g.draw(v); err != nil {
+			return err
+		}
+	}
+
+	Screen.Show()
+	return nil
+}
+
 // draw manages the cursor and calls the draw function of a view.
 func (g *Gui) draw(v *View) error {
 	if g.suspended {

pkg/gui/gui.go

@@ -1188,6 +1188,12 @@ func (gui *Gui) onUIThread(f func() error) {
 	})
 }
 
+func (gui *Gui) onUIThreadContentOnly(f func() error) {
+	gui.g.UpdateContentOnly(func(*gocui.Gui) error {
+		return f()
+	})
+}
+
 func (gui *Gui) onWorker(f func(gocui.Task) error) {
 	gui.g.OnWorker(f)
 }

pkg/gui/gui_common.go

@@ -120,6 +120,10 @@ func (self *guiCommon) OnUIThread(f func() error) {
 	self.gui.onUIThread(f)
 }
 
+func (self *guiCommon) OnUIThreadContentOnly(f func() error) {
+	self.gui.onUIThreadContentOnly(f)
+}
+
 func (self *guiCommon) OnWorker(f func(gocui.Task) error) {
 	self.gui.onWorker(f)
 }

pkg/gui/types/common.go

@@ -71,6 +71,10 @@ type IGuiCommon interface {
 	// Only necessary to call if you're not already on the UI thread i.e. you're inside a goroutine.
 	// All controller handlers are executed on the UI thread.
 	OnUIThread(f func() error)
+	// Like OnUIThread, but signals that the callback only modifies view
+	// content (e.g. spinner), allows the event loop to skip
+	// the expensive layout recalculation when only content changed.
+	OnUIThreadContentOnly(f func() error)
 	// Runs a function in a goroutine. Use this whenever you want to run a goroutine and keep track of the fact
 	// that lazygit is still busy. See docs/dev/Busy.md
 	OnWorker(f func(gocui.Task) error)