Add --no-alternate-screen (-X) flag

cmd/moor/moor.go

@@ -131,11 +131,7 @@ func parseStyleOption(styleOption string) (*chroma.Style, error) {
 
 func parseColorsOption(colorsOption string) (twin.ColorCount, error) {
 	if strings.ToLower(colorsOption) == "auto" {
-		colorsOption = "16M"
-		if os.Getenv("COLORTERM") != "truecolor" && strings.Contains(os.Getenv("TERM"), "256") {
-			// Covers "xterm-256color" as used by the macOS Terminal
-			colorsOption = "256"
-		}
+		return twin.DefaultColorCount(), nil
 	}
 
 	switch strings.ToUpper(colorsOption) {
@@ -397,7 +393,7 @@ func getVersion() string {
 // Can return a nil pager on --help or --version, or if pumping to stdout.
 func pagerFromArgs(
 	args []string,
-	newScreen func(mouseMode twin.MouseMode, terminalColorCount twin.ColorCount) (twin.Screen, error),
+	newScreen func(options twin.ScreenOptions) (twin.Screen, error),
 	stdinIsRedirected bool,
 	stdoutIsRedirected bool,
 ) (
@@ -438,6 +434,8 @@ func pagerFromArgs(
 	flagSet.Bool("no-reformat", true, "No effect, kept for compatibility. See --reformat")
 	quitIfOneScreen := flagSet.Bool("quit-if-one-screen", false, "Don't page if contents fits on one screen. Affected by --no-clear-on-exit-margin.")
 	noClearOnExit := flagSet.Bool("no-clear-on-exit", false, "Retain screen contents when exiting moor")
+	noAlternateScreen := flagSet.Bool("no-alternate-screen", false, "Don't use the alternate screen buffer (like less -X)")
+	flagSet.BoolVar(noAlternateScreen, "X", false, "Don't use the alternate screen buffer (like less -X)")
 	noClearOnExitMargin := flagSet.Int("no-clear-on-exit-margin", 1,
 		"Number of lines to leave for your shell prompt, defaults to 1")
 	statusBarStyle := flagSetFunc(flagSet, "statusbar", internal.STATUSBAR_STYLE_INVERSE,
@@ -619,7 +617,11 @@ func pagerFromArgs(
 
 	// We got the first byte, this means sudo is done (if it was used) and we
 	// can set up the UI.
-	screen, err := newScreen(*mouseMode, *terminalColorsCount)
+	screen, err := newScreen(twin.ScreenOptions{
+		MouseMode:          *mouseMode,
+		ColorCount:         *terminalColorsCount,
+		UseAlternateScreen: !*noAlternateScreen,
+	})
 	if err != nil {
 		// Ref: https://github.com/walles/moor/issues/149
 		log.Info("Failed to set up screen for paging, pumping to stdout instead: ", err)
@@ -710,7 +712,7 @@ func main() {
 
 	pager, screen, style, formatter, _logsRequested, err := pagerFromArgs(
 		os.Args,
-		twin.NewScreenWithMouseModeAndColorCount,
+		twin.NewScreenWithOptions,
 		stdinIsRedirected,
 		stdoutIsRedirected,
 	)

cmd/moor/moor_test.go

@@ -32,7 +32,7 @@ func TestUnescapeManPn(t *testing.T) {
 func TestPageOneInputFile(t *testing.T) {
 	pager, screen, _, formatter, _, err := pagerFromArgs(
 		[]string{"", "moor_test.go"},
-		func(_ twin.MouseMode, _ twin.ColorCount) (twin.Screen, error) {
+		func(_ twin.ScreenOptions) (twin.Screen, error) {
 			return twin.NewFakeScreen(80, 24), nil
 		},
 		false, // stdin is redirected

moor.1

@@ -60,6 +60,10 @@ Guarantee selecting text with the mouse works but maybe not mouse scrolling.
 Or guarantee mouse scrolling works but selecting text requiring extra effort.
 Details here: https://github.com/walles/moor/blob/master/MOUSE.md
 .TP
+\fB\-\-no\-alternate\-screen\fR, \fB\-X\fR
+Don't use the alternate screen buffer. This is useful for seeing prompts
+written to the main terminal screen by concurrent processes.
+.TP
 \fB\-\-no\-clear\-on\-exit\fR
 Retain screen contents when exiting moor.
 Affected by \fB--no-clear-on-exit-margin\fP.

pkg/moor/embed-api.go

@@ -44,6 +44,10 @@ type Options struct {
 	// The default is to always start the pager. If this is set to true, short
 	// input will just be printed, and no paging will happen.
 	QuitIfOneScreen bool
+
+	// The default is to use the alternate screen buffer. Set this to true to
+	// disable the alternate screen buffer.
+	NoAlternateScreen bool
 }
 
 // PageFromStream reads the contents of the given reader and presents it in a pager.
@@ -161,7 +165,11 @@ func pageFromReader(reader *internalReader.ReaderImpl, options Options) error {
 	pager.ShowLineNumbers = !options.NoLineNumbers
 	pager.QuitIfOneScreen = options.QuitIfOneScreen
 
-	screen, e := twin.NewScreen()
+	screen, e := twin.NewScreenWithOptions(twin.ScreenOptions{
+		MouseMode:          twin.MouseModeAuto,
+		ColorCount:         twin.DefaultColorCount(),
+		UseAlternateScreen: !options.NoAlternateScreen,
+	})
 	if e != nil {
 		// Screen setup failed
 		return e

twin/screen.go

@@ -84,6 +84,12 @@ type lastRendered struct {
 	cells  [][]StyledRune
 }
 
+type ScreenOptions struct {
+	MouseMode          MouseMode
+	ColorCount         ColorCount
+	UseAlternateScreen bool
+}
+
 type UnixScreen struct {
 	widthAccessFromSizeOnly  int // Access from Size() method only
 	heightAccessFromSizeOnly int // Access from Size() method only
@@ -116,6 +122,7 @@ type UnixScreen struct {
 
 	terminalColorCount ColorCount
 	mouseMode          MouseMode
+	useAlternateScreen bool
 }
 
 // Example event: "\x1b[<65;127;41M"
@@ -135,22 +142,34 @@ func NewScreen() (Screen, error) {
 }
 
 func NewScreenWithMouseMode(mouseMode MouseMode) (Screen, error) {
-	terminalColorCount := ColorCount24bit
+	return NewScreenWithMouseModeAndColorCount(mouseMode, DefaultColorCount())
+}
+
+func DefaultColorCount() ColorCount {
 	if os.Getenv("COLORTERM") != "truecolor" && strings.Contains(os.Getenv("TERM"), "256") {
 		// Covers "xterm-256color" as used by the macOS Terminal
-		terminalColorCount = ColorCount256
+		return ColorCount256
 	}
-	return NewScreenWithMouseModeAndColorCount(mouseMode, terminalColorCount)
+	return ColorCount24bit
 }
 
 func NewScreenWithMouseModeAndColorCount(mouseMode MouseMode, terminalColorCount ColorCount) (Screen, error) {
+	return NewScreenWithOptions(ScreenOptions{
+		MouseMode:          mouseMode,
+		ColorCount:         terminalColorCount,
+		UseAlternateScreen: true,
+	})
+}
+
+func NewScreenWithOptions(options ScreenOptions) (Screen, error) {
 	if !term.IsTerminal(int(os.Stdout.Fd())) {
 		return nil, fmt.Errorf("stdout (fd=%d) must be a terminal for paging to work", os.Stdout.Fd())
 	}
 
 	screen := UnixScreen{
-		terminalColorCount: terminalColorCount,
-		mouseMode:          mouseMode,
+		terminalColorCount: options.ColorCount,
+		mouseMode:          options.MouseMode,
+		useAlternateScreen: options.UseAlternateScreen,
 	}
 
 	// The number "80" here is from manual testing on my MacBook:
@@ -177,7 +196,7 @@ func NewScreenWithMouseModeAndColorCount(mouseMode MouseMode, terminalColorCount
 
 	go func() {
 		defer func() {
-			panicHandler("NewScreenWithMouseModeAndColorCount()/mainLoop()", recover(), debug.Stack())
+			panicHandler("NewScreenWithOptions()/mainLoop()", recover(), debug.Stack())
 		}()
 
 		screen.mainLoop()
@@ -271,7 +290,9 @@ func (screen *UnixScreen) enterAlternateScreenSession() {
 	screen.renderLock.Lock()
 	defer screen.renderLock.Unlock()
 
-	screen.setAlternateScreenModeLocked(true)
+	if screen.useAlternateScreen {
+		screen.setAlternateScreenModeLocked(true)
+	}
 	screen.enableMouseTrackingLocked(screen.shouldEnableMouseTracking())
 	screen.hideCursorLocked(true)
 
@@ -288,7 +309,9 @@ func (screen *UnixScreen) leaveAlternateScreenSession() {
 	screen.writeLocked("\x1b[m")
 	screen.hideCursorLocked(false)
 	screen.enableMouseTrackingLocked(false)
-	screen.setAlternateScreenModeLocked(false)
+	if screen.useAlternateScreen {
+		screen.setAlternateScreenModeLocked(false)
+	}
 }
 
 func (screen *UnixScreen) shouldEnableMouseTracking() bool {