fix: maintain cursor visibility across altscreen state switch

Based on charmbracelet#462 and charmbracelet#452 by @londek, but fixes maintaining the
current visibility state across altscreen state changes.

This makes the behavior consistent across terminals, some of which
keep separate state for altscreen and regular buffer.

Fixes charmbracelet#190.

screen_test.go

@@ -19,12 +19,12 @@ func TestClearMsg(t *testing.T) {
 		{
 			name:     "altscreen",
 			cmds:     []Cmd{EnterAltScreen, ExitAltScreen},
-			expected: "\x1b[?25l\x1b[?1049h\x1b[2J\x1b[1;1H\x1b[1;1H\x1b[?1049lsuccess\r\n\x1b[0D\x1b[2K\x1b[?25h\x1b[?1002l\x1b[?1003l",
+			expected: "\x1b[?25l\x1b[?1049h\x1b[2J\x1b[1;1H\x1b[1;1H\x1b[?25l\x1b[?1049l\x1b[?25lsuccess\r\n\x1b[0D\x1b[2K\x1b[?25h\x1b[?1002l\x1b[?1003l",
 		},
 		{
 			name:     "altscreen_autoexit",
 			cmds:     []Cmd{EnterAltScreen},
-			expected: "\x1b[?25l\x1b[?1049h\x1b[2J\x1b[1;1H\x1b[1;1Hsuccess\r\n\x1b[2;0H\x1b[2K\x1b[?25h\x1b[?1002l\x1b[?1003l\x1b[?1049l",
+			expected: "\x1b[?25l\x1b[?1049h\x1b[2J\x1b[1;1H\x1b[1;1H\x1b[?25lsuccess\r\n\x1b[2;0H\x1b[2K\x1b[?25h\x1b[?1002l\x1b[?1003l\x1b[?1049l\x1b[?25h",
 		},
 		{
 			name:     "mouse_cellmotion",

standard_renderer.go

@@ -38,6 +38,9 @@ type standardRenderer struct {
 	useANSICompressor  bool
 	once               sync.Once
 
+	// cursor visibility state
+	cursorHidden bool
+
 	// essentially whether or not we're using the full size of the terminal
 	altScreenActive bool
 
@@ -299,6 +302,15 @@ func (r *standardRenderer) enterAltScreen() {
 	r.out.ClearScreen()
 	r.out.MoveCursor(1, 1)
 
+	// cmd.exe and other terminals keep separate cursor states for the AltScreen
+	// and the main buffer. We have to explicitly reset the cursor visibility
+	// whenever we enter AltScreen.
+	if r.cursorHidden {
+		r.out.HideCursor()
+	} else {
+		r.out.ShowCursor()
+	}
+
 	r.repaint()
 }
 
@@ -313,20 +325,31 @@ func (r *standardRenderer) exitAltScreen() {
 	r.altScreenActive = false
 	r.out.ExitAltScreen()
 
+	// cmd.exe and other terminals keep separate cursor states for the AltScreen
+	// and the main buffer. We have to explicitly reset the cursor visibility
+	// whenever we exit AltScreen.
+	if r.cursorHidden {
+		r.out.HideCursor()
+	} else {
+		r.out.ShowCursor()
+	}
+
 	r.repaint()
 }
 
 func (r *standardRenderer) showCursor() {
 	r.mtx.Lock()
 	defer r.mtx.Unlock()
 
+	r.cursorHidden = false
 	r.out.ShowCursor()
 }
 
 func (r *standardRenderer) hideCursor() {
 	r.mtx.Lock()
 	defer r.mtx.Unlock()
 
+	r.cursorHidden = true
 	r.out.HideCursor()
 }