fix: bug with empty lines

pkg/mux/screen/replay/replay_test.go

@@ -65,15 +65,15 @@ func TestSearch(t *testing.T) {
 
 func TestIndex(t *testing.T) {
 	var r = newReplay(createTestSession(), bind.NewEngine[bind.Action]())
-	r.setIndex(2, 0)
+	r.gotoIndex(2, 0)
 	require.Equal(t, "t ", r.getLine(0).String()[:2])
-	r.setIndex(2, 1)
+	r.gotoIndex(2, 1)
 	require.Equal(t, "te ", r.getLine(0).String()[:3])
-	r.setIndex(2, 0)
+	r.gotoIndex(2, 0)
 	require.Equal(t, "t ", r.getLine(0).String()[:2])
-	r.setIndex(2, -1)
+	r.gotoIndex(2, -1)
 	require.Equal(t, "test", r.getLine(0).String()[:4])
-	r.setIndex(4, -1)
+	r.gotoIndex(4, -1)
 	require.Equal(t, "take", r.getLine(0).String()[:4])
 }
 
@@ -86,8 +86,8 @@ func TestViewport(t *testing.T) {
 	var r = newReplay(s.Events(), bind.NewEngine[bind.Action]())
 	input(r, geom.Size{R: 10, C: 10})
 	require.Equal(t, geom.Vec2{R: 0, C: 0}, r.minOffset)
-	require.Equal(t, geom.Vec2{R: 10, C: 10}, r.maxOffset)
-	require.Equal(t, geom.Vec2{R: 10, C: 10}, r.offset)
+	require.Equal(t, geom.Vec2{R: 11, C: 10}, r.maxOffset)
+	require.Equal(t, geom.Vec2{R: 11, C: 10}, r.offset)
 }
 
 func TestScroll(t *testing.T) {
@@ -105,7 +105,7 @@ func TestScroll(t *testing.T) {
 	)
 
 	var r = newReplay(s.Events(), bind.NewEngine[bind.Action]())
-	input(r, geom.Size{R: 2, C: 10})
+	input(r, geom.Size{R: 3, C: 10})
 	require.Equal(t, 1, r.cursor.R)
 	require.Equal(t, 5, r.cursor.C)
 	require.Equal(t, 5, r.desiredCol)
@@ -155,7 +155,7 @@ func TestCursor(t *testing.T) {
 	)
 
 	var r = newReplay(s.Events(), bind.NewEngine[bind.Action]())
-	input(r, geom.Size{R: 2, C: 10})
+	input(r, geom.Size{R: 3, C: 10})
 	require.Equal(t, 2, r.offset.R)
 	require.Equal(t, 1, r.cursor.R)
 	require.Equal(t, 4, r.cursor.C)
@@ -187,3 +187,13 @@ func TestCursor(t *testing.T) {
 		C: 0,
 	}, r.viewportToTerm(r.cursor))
 }
+
+func TestEmpty(t *testing.T) {
+	s := sessions.NewSimulator()
+	s.Add(
+		geom.Size{R: 5, C: 10},
+	)
+
+	var r = newReplay(s.Events(), bind.NewEngine[bind.Action]())
+	input(r, geom.Size{R: 3, C: 10}, ActionCursorDown)
+}

pkg/mux/screen/replay/screen.go

@@ -166,9 +166,16 @@ func (r *Replay) recalculateViewport() {
 
 // Get the glyphs for a row in term space.
 func (r *Replay) getLine(row int) emu.Line {
-	var line emu.Line
 	screen := r.terminal.Screen()
 	history := r.terminal.History()
+
+	// Handle out-of-bounds lines
+	clamped := geom.Clamp(row, -len(history), r.getTerminalSize().R-1)
+	if clamped != row {
+		return nil
+	}
+
+	var line emu.Line
 	if row < 0 {
 		line = history[len(history)+row]
 	} else {
@@ -238,6 +245,10 @@ func getNonWhitespace(line emu.Line) (first, last int) {
 // and down in a text editor.
 func (r *Replay) resolveDesiredColumn(point geom.Vec2) int {
 	line := r.getLine(point.R)
+	if line == nil {
+		return 0
+	}
+
 	occupancy := getOccupancy(line)
 
 	// desiredCol occupied -> return that col
@@ -369,6 +380,9 @@ func (r *Replay) moveCursorDelta(dy, dx int) {
 	// Motion to the right is bounded to the last non-whitespace character
 	if newPos.C > oldPos.C {
 		line := r.getLine(newPos.R)
+		if line == nil {
+			return
+		}
 		_, lastCell := getNonWhitespace(line)
 		newPos.C = geom.Min(lastCell, newPos.C)
 	}