feat: support changing the cursor style

cursor.go

@@ -8,3 +8,39 @@
 	// Column is the column number.
 	Column int
 }
+
+// CursorStyle is a style that represents the terminal cursor.
+type CursorStyle int
+
+// Cursor styles.
+const (
+	CursorBlock CursorStyle = iota
+	CursorUnderline
+	CursorBar
+)
+
+// setCursorStyle is an internal message that sets the cursor style. This matches the
+// ANSI escape sequence values for cursor styles. This includes:
+//
+//	0: Blinking block
+//	1: Blinking block (default)
+//	2: Steady block
+//	3: Blinking underline
+//	4: Steady underline
+//	5: Blinking bar (xterm)
+//	6: Steady bar (xterm)
+type setCursorStyle int
+
+// SetCursorStyle is a command that sets the terminal cursor style. Steady
+// determines if the cursor should blink or not.
+func SetCursorStyle(style CursorStyle, steady bool) Cmd {
+	// We're using the ANSI escape sequence values for cursor styles.
+	// We need to map both [style] and [steady] to the correct value.
+	style = (style * 2) + 1
+	if steady {
+		style++
+	}
+	return func() Msg {
+		return setCursorStyle(style)
+	}
+}

examples/cursor-style/main.go

@@ -0,0 +1,61 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	tea "github.com/charmbracelet/bubbletea/v2"
+)
+
+type model struct {
+	style  tea.CursorStyle
+	steady bool
+}
+
+func (m model) Init() (tea.Model, tea.Cmd) {
+	return m, tea.ShowCursor
+}
+
+func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
+	var cmd tea.Cmd
+	switch msg := msg.(type) {
+	case tea.KeyPressMsg:
+		switch msg.String() {
+		case "ctrl+q", "q":
+			return m, tea.Quit
+		case "left":
+			if m.style == tea.CursorBlock && !m.steady {
+				break
+			}
+			if !m.steady {
+				m.style--
+			}
+			m.steady = !m.steady
+			cmd = tea.SetCursorStyle(m.style, m.steady)
+		case "right":
+			if m.style == tea.CursorBar && m.steady {
+				break
+			}
+			if m.steady {
+				m.style++
+			}
+			m.steady = !m.steady
+			cmd = tea.SetCursorStyle(m.style, m.steady)
+		}
+	}
+	return m, cmd
+}
+
+func (m model) View() string {
+	return "Press left/right to change the cursor style, q or ctrl+c to quit." +
+		"\n\n" +
+		"  <- This is a cursor"
+}
+
+func main() {
+	p := tea.NewProgram(model{})
+	if _, err := p.Run(); err != nil {
+		fmt.Fprintf(os.Stderr, "Error: %v", err)
+		os.Exit(1)
+	}
+}

tea.go

@@ -429,6 +429,9 @@ func (p *Program) eventLoop(model Model, cmds chan Cmd) (Model, error) {
 					p.suspend()
 				}
 
+			case setCursorStyle:
+				p.execute(ansi.SetCursorStyle(int(msg)))
+
 			case modeReportMsg:
 				switch msg.Mode {
 				case graphemeClustering: