Include stack trace in panic logs

Fixes #237.

m/pager.go

@@ -3,6 +3,7 @@ package m
 import (
 	"fmt"
 	"regexp"
+	"runtime/debug"
 	"strings"
 	"time"
 
@@ -323,7 +324,7 @@ func (p *Pager) StartPaging(screen twin.Screen, chromaStyle *chroma.Style, chrom
 
 	go func() {
 		defer func() {
-			panicHandler("StartPaging()/moreLinesAvailable", recover())
+			panicHandler("StartPaging()/moreLinesAvailable", recover(), debug.Stack())
 		}()
 
 		for range p.reader.moreLinesAdded {
@@ -342,7 +343,7 @@ func (p *Pager) StartPaging(screen twin.Screen, chromaStyle *chroma.Style, chrom
 
 	go func() {
 		defer func() {
-			panicHandler("StartPaging()/spinner", recover())
+			panicHandler("StartPaging()/spinner", recover(), debug.Stack())
 		}()
 
 		// Spin the spinner as long as contents is still loading
@@ -368,7 +369,7 @@ func (p *Pager) StartPaging(screen twin.Screen, chromaStyle *chroma.Style, chrom
 
 	go func() {
 		defer func() {
-			panicHandler("StartPaging()/maybeDone", recover())
+			panicHandler("StartPaging()/maybeDone", recover(), debug.Stack())
 		}()
 
 		for range p.reader.maybeDone {

m/panicHandler.go

@@ -6,12 +6,13 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
-func panicHandler(goroutineName string, recoverResult any) {
+func panicHandler(goroutineName string, recoverResult any, stackTrace []byte) {
 	if recoverResult == nil {
 		return
 	}
 
 	log.WithFields(log.Fields{
-		"recoverResult": recoverResult,
+		"panic":      recoverResult,
+		"stackTrace": string(stackTrace),
 	}).Error("Goroutine panicked: " + goroutineName)
 }

m/reader.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"os"
 	"path"
+	"runtime/debug"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -366,7 +367,7 @@ func newReaderFromStream(reader io.Reader, originalFileName *string, formatter c
 
 	go func() {
 		defer func() {
-			panicHandler("newReaderFromStream()/readStream()", recover())
+			panicHandler("newReaderFromStream()/readStream()", recover(), debug.Stack())
 		}()
 
 		returnMe.readStream(reader, formatter, lexer)

m/search.go

@@ -3,6 +3,7 @@ package m
 import (
 	"fmt"
 	"runtime"
+	"runtime/debug"
 	"time"
 
 	log "github.com/sirupsen/logrus"
@@ -125,7 +126,7 @@ func (p *Pager) findFirstHit(startPosition linenumbers.LineNumber, beforePositio
 
 		go func(i int, searchStart linenumbers.LineNumber, chunkBefore *linenumbers.LineNumber) {
 			defer func() {
-				panicHandler("findFirstHit()/chunkSearch", recover())
+				panicHandler("findFirstHit()/chunkSearch", recover(), debug.Stack())
 			}()
 
 			findings[i] <- p._findFirstHit(searchStart, chunkBefore, backwards)

m/textstyles/ansiTokenizer.go

@@ -511,6 +511,18 @@ func rawUpdateStyle(style twin.Style, escapeSequenceWithoutHeader string, number
 		case 49:
 			style = style.WithBackground(twin.ColorDefault)
 
+		case 58:
+			var err error
+			var color *twin.Color
+			index, color, err = consumeCompositeColor(numbersBuffer, index-1)
+			if err != nil {
+				return style, numbersBuffer, fmt.Errorf("Underline: %w", err)
+			}
+			style = style.WithUnderlineColor(*color)
+
+		case 59:
+			style = style.WithUnderlineColor(twin.ColorDefault)
+
 		// Bright foreground colors: see https://pkg.go.dev/github.com/gdamore/Color
 		//
 		// After testing vs less and cat on iTerm2 3.3.9 / macOS Catalina
@@ -573,9 +585,9 @@ func joinUints(ints []uint) string {
 // * A color value that can be applied to a style
 func consumeCompositeColor(numbers []uint, index int) (int, *twin.Color, error) {
 	baseIndex := index
-	if numbers[index] != 38 && numbers[index] != 48 {
+	if numbers[index] != 38 && numbers[index] != 48 && numbers[index] != 58 {
 		err := fmt.Errorf(
-			"unknown start of color sequence <%d>, expected 38 (foreground) or 48 (background): <CSI %sm>",
+			"unknown start of color sequence <%d>, expected 38 (foreground), 48 (background) or 58 (underline): <CSI %sm>",
 			numbers[index],
 			joinUints(numbers[baseIndex:]))
 		return -1, nil, err

m/textstyles/ansiTokenizer_test.go

@@ -216,7 +216,7 @@ func TestConsumeCompositeColorBadPrefix(t *testing.T) {
 	// 8 bit color
 	// Example from: https://github.com/walles/moar/issues/14
 	_, color, err := consumeCompositeColor([]uint{29}, 0)
-	assert.Equal(t, err.Error(), "unknown start of color sequence <29>, expected 38 (foreground) or 48 (background): <CSI 29m>")
+	assert.Equal(t, err.Error(), "unknown start of color sequence <29>, expected 38 (foreground), 48 (background) or 58 (underline): <CSI 29m>")
 	assert.Assert(t, color == nil)
 }
 

moar.go

@@ -38,7 +38,7 @@ const defaultLightTheme = "tango"
 
 var versionString = "Should be set when building, please use build.sh to build"
 
-func renderLessTermcapEnvVar(envVarName string, description string, colors twin.ColorType) string {
+func renderLessTermcapEnvVar(envVarName string, description string, colors twin.ColorCount) string {
 	value := os.Getenv(envVarName)
 	if len(value) == 0 {
 		return ""
@@ -67,7 +67,7 @@ func renderLessTermcapEnvVar(envVarName string, description string, colors twin.
 	)
 }
 
-func renderPagerEnvVar(name string, colors twin.ColorType) string {
+func renderPagerEnvVar(name string, colors twin.ColorCount) string {
 	bold := twin.StyleDefault.WithAttr(twin.AttrBold).RenderUpdateFrom(twin.StyleDefault, colors)
 	notBold := twin.StyleDefault.RenderUpdateFrom(twin.StyleDefault.WithAttr(twin.AttrBold), colors)
 
@@ -129,14 +129,14 @@ func printCommandline(output io.Writer) {
 	fmt.Fprintln(output)
 }
 
-func heading(text string, colors twin.ColorType) string {
+func heading(text string, colors twin.ColorCount) string {
 	style := twin.StyleDefault.WithAttr(twin.AttrItalic)
 	prefix := style.RenderUpdateFrom(twin.StyleDefault, colors)
 	suffix := twin.StyleDefault.RenderUpdateFrom(style, colors)
 	return prefix + text + suffix
 }
 
-func printUsage(flagSet *flag.FlagSet, colors twin.ColorType) {
+func printUsage(flagSet *flag.FlagSet, colors twin.ColorCount) {
 	// This controls where PrintDefaults() prints, see below
 	flagSet.SetOutput(os.Stdout)
 
@@ -315,7 +315,7 @@ func parseStyleOption(styleOption string) (*chroma.Style, error) {
 	return style, nil
 }
 
-func parseColorsOption(colorsOption string) (twin.ColorType, 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") {
@@ -326,16 +326,16 @@ func parseColorsOption(colorsOption string) (twin.ColorType, error) {
 
 	switch strings.ToUpper(colorsOption) {
 	case "8":
-		return twin.ColorType8, nil
+		return twin.ColorCount8, nil
 	case "16":
-		return twin.ColorType16, nil
+		return twin.ColorCount16, nil
 	case "256":
-		return twin.ColorType256, nil
+		return twin.ColorCount256, nil
 	case "16M":
-		return twin.ColorType24bit, nil
+		return twin.ColorCount24bit, nil
 	}
 
-	var noColor twin.ColorType
+	var noColor twin.ColorCount
 	return noColor, fmt.Errorf("Valid counts are 8, 16, 256, 16M or auto")
 }
 
@@ -519,7 +519,7 @@ func noLineNumbersDefault() bool {
 // 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.ColorType) (twin.Screen, error),
+	newScreen func(mouseMode twin.MouseMode, terminalColorCount twin.ColorCount) (twin.Screen, error),
 	stdinIsRedirected bool,
 	stdoutIsRedirected bool,
 ) (
@@ -674,11 +674,11 @@ func pagerFromArgs(
 	}
 
 	formatter := formatters.TTY256
-	if *terminalColorsCount == twin.ColorType8 {
+	if *terminalColorsCount == twin.ColorCount8 {
 		formatter = formatters.TTY8
-	} else if *terminalColorsCount == twin.ColorType16 {
+	} else if *terminalColorsCount == twin.ColorCount16 {
 		formatter = formatters.TTY16
-	} else if *terminalColorsCount == twin.ColorType24bit {
+	} else if *terminalColorsCount == twin.ColorCount24bit {
 		formatter = formatters.TTY16m
 	}
 
@@ -803,7 +803,7 @@ func main() {
 
 	pager, screen, style, formatter, err := pagerFromArgs(
 		os.Args,
-		twin.NewScreenWithMouseModeAndColorType,
+		twin.NewScreenWithMouseModeAndColorCount,
 		stdinIsRedirected,
 		stdoutIsRedirected,
 	)

moar_test.go

@@ -19,7 +19,7 @@ func TestParseScrollHint(t *testing.T) {
 func TestPageOneInputFile(t *testing.T) {
 	pager, screen, _, formatter, err := pagerFromArgs(
 		[]string{"", "moar_test.go"},
-		func(_ twin.MouseMode, _ twin.ColorType) (twin.Screen, error) {
+		func(_ twin.MouseMode, _ twin.ColorCount) (twin.Screen, error) {
 			return twin.NewFakeScreen(80, 24), nil
 		},
 		false, // stdin is redirected

sample-files/colored-underlines.txt

@@ -0,0 +1 @@
+[58:5:196mRed underline Default colored underline

twin/colors.go

@@ -10,30 +10,39 @@ import (
 // Create using NewColor16(), NewColor256 or NewColor24Bit(), or use
 // ColorDefault.
 type Color uint32
-type ColorType uint8
+
+type ColorCount uint8
 
 const (
 	// Default foreground / background color
-	ColorTypeDefault ColorType = iota
+	ColorCountDefault ColorCount = iota
 
 	// https://en.wikipedia.org/wiki/ANSI_escape_code#3-bit_and_4-bit
 	//
 	// Note that this type is only used for output, on input we store 3 bit
 	// colors as 4 bit colors since they map to the same values.
-	ColorType8
+	ColorCount8
 
 	// https://en.wikipedia.org/wiki/ANSI_escape_code#3-bit_and_4-bit
-	ColorType16
+	ColorCount16
 
 	// https://en.wikipedia.org/wiki/ANSI_escape_code#8-bit
-	ColorType256
+	ColorCount256
 
 	// RGB: https://en.wikipedia.org/wiki/ANSI_escape_code#24-bit
-	ColorType24bit
+	ColorCount24bit
+)
+
+type colorType uint8
+
+const (
+	colorTypeForeground colorType = iota
+	colorTypeBackground
+	colorTypeUnderline
 )
 
 // Reset to default foreground / background color
-var ColorDefault = newColor(ColorTypeDefault, 0)
+var ColorDefault = newColor(ColorCountDefault, 0)
 
 // From: https://en.wikipedia.org/wiki/ANSI_escape_code#3-bit_and_4-bit
 var colorNames16 = map[int]string{
@@ -55,30 +64,30 @@ var colorNames16 = map[int]string{
 	15: "15 bright white",
 }
 
-func newColor(colorType ColorType, value uint32) Color {
-	return Color(value | (uint32(colorType) << 24))
+func newColor(colorCount ColorCount, value uint32) Color {
+	return Color(value | (uint32(colorCount) << 24))
 }
 
 // Four bit colors as defined here:
 // https://en.wikipedia.org/wiki/ANSI_escape_code#3-bit_and_4-bit
 func NewColor16(colorNumber0to15 int) Color {
-	return newColor(ColorType16, uint32(colorNumber0to15))
+	return newColor(ColorCount16, uint32(colorNumber0to15))
 }
 
 func NewColor256(colorNumber uint8) Color {
-	return newColor(ColorType256, uint32(colorNumber))
+	return newColor(ColorCount256, uint32(colorNumber))
 }
 
 func NewColor24Bit(red uint8, green uint8, blue uint8) Color {
-	return newColor(ColorType24bit, (uint32(red)<<16)+(uint32(green)<<8)+(uint32(blue)<<0))
+	return newColor(ColorCount24bit, (uint32(red)<<16)+(uint32(green)<<8)+(uint32(blue)<<0))
 }
 
 func NewColorHex(rgb uint32) Color {
-	return newColor(ColorType24bit, rgb)
+	return newColor(ColorCount24bit, rgb)
 }
 
-func (color Color) ColorType() ColorType {
-	return ColorType(color >> 24)
+func (color Color) ColorCount() ColorCount {
+	return ColorCount(color >> 24)
 }
 
 func (color Color) colorValue() uint32 {
@@ -88,100 +97,105 @@ func (color Color) colorValue() uint32 {
 // Render color into an ANSI string.
 //
 // Ref: https://en.wikipedia.org/wiki/ANSI_escape_code#SGR_(Select_Graphic_Rendition)_parameters
-func (color Color) ansiString(foreground bool, terminalColorCount ColorType) string {
-	fgBgMarker := "3"
-	if !foreground {
-		fgBgMarker = "4"
+func (color Color) ansiString(cType colorType, terminalColorCount ColorCount) string {
+	var typeMarker string
+	if cType == colorTypeForeground {
+		typeMarker = "3"
+	} else if cType == colorTypeBackground {
+		typeMarker = "4"
+	} else if cType == colorTypeUnderline {
+		typeMarker = "5"
+	} else {
+		panic(fmt.Errorf("unhandled color type %d", cType))
 	}
 
-	if color.ColorType() == ColorTypeDefault {
-		return fmt.Sprint("\x1b[", fgBgMarker, "9m")
+	if color.ColorCount() == ColorCountDefault {
+		return fmt.Sprint("\x1b[", typeMarker, "9m")
 	}
 
 	color = color.downsampleTo(terminalColorCount)
 
-	if color.ColorType() == ColorType16 {
+	// We never create any ColorCount8 colors, but we store them as
+	// ColorCount16. So this if() statement will cover both.
+	if color.ColorCount() == ColorCount16 {
+		if cType == colorTypeUnderline {
+			// Only 256 and 24 bit colors supported for underline color
+			return ""
+		}
+
 		value := color.colorValue()
 		if value < 8 {
-			return fmt.Sprint("\x1b[", fgBgMarker, value, "m")
+			return fmt.Sprint("\x1b[", typeMarker, value, "m")
 		} else if value <= 15 {
-			fgBgMarker := "9"
-			if !foreground {
-				fgBgMarker = "10"
+			typeMarker := "9"
+			if cType == colorTypeBackground {
+				typeMarker = "10"
 			}
-			return fmt.Sprint("\x1b[", fgBgMarker, value-8, "m")
+			return fmt.Sprint("\x1b[", typeMarker, value-8, "m")
 		}
+
+		panic(fmt.Errorf("unhandled color16 value %d", value))
 	}
 
-	if color.ColorType() == ColorType256 {
+	if color.ColorCount() == ColorCount256 {
 		value := color.colorValue()
 		if value <= 255 {
-			return fmt.Sprint("\x1b[", fgBgMarker, "8;5;", value, "m")
+			return fmt.Sprint("\x1b[", typeMarker, "8;5;", value, "m")
 		}
 	}
 
-	if color.ColorType() == ColorType24bit {
+	if color.ColorCount() == ColorCount24bit {
 		value := color.colorValue()
 		red := (value & 0xff0000) >> 16
 		green := (value & 0xff00) >> 8
 		blue := value & 0xff
 
-		return fmt.Sprint("\x1b[", fgBgMarker, "8;2;", red, ";", green, ";", blue, "m")
+		return fmt.Sprint("\x1b[", typeMarker, "8;2;", red, ";", green, ";", blue, "m")
 	}
 
-	panic(fmt.Errorf("unhandled color type=%d %s", color.ColorType(), color.String()))
-}
-
-func (color Color) ForegroundAnsiString(terminalColorCount ColorType) string {
-	// FIXME: Test this function with all different color types.
-	return color.ansiString(true, terminalColorCount)
-}
-
-func (color Color) BackgroundAnsiString(terminalColorCount ColorType) string {
-	// FIXME: Test this function with all different color types.
-	return color.ansiString(false, terminalColorCount)
+	panic(fmt.Errorf("unhandled color type=%d %s", color.ColorCount(), color.String()))
 }
 
 func (color Color) String() string {
-	switch color.ColorType() {
-	case ColorTypeDefault:
+	switch color.ColorCount() {
+	case ColorCountDefault:
 		return "Default color"
 
-	case ColorType16:
+	case ColorCount16:
 		return colorNames16[int(color.colorValue())]
 
-	case ColorType256:
+	case ColorCount256:
 		if color.colorValue() < 16 {
 			return colorNames16[int(color.colorValue())]
 		}
 		return fmt.Sprintf("#%02x", color.colorValue())
 
-	case ColorType24bit:
+	case ColorCount24bit:
 		return fmt.Sprintf("#%06x", color.colorValue())
 	}
 
-	panic(fmt.Errorf("unhandled color type %d", color.ColorType()))
+	panic(fmt.Errorf("unhandled color type %d", color.ColorCount()))
 }
 
 func (color Color) to24Bit() Color {
-	if color.ColorType() == ColorType24bit {
+	if color.ColorCount() == ColorCount24bit {
 		return color
 	}
 
-	if color.ColorType() == ColorType8 || color.ColorType() == ColorType16 || color.ColorType() == ColorType256 {
+	if color.ColorCount() == ColorCount8 || color.ColorCount() == ColorCount16 || color.ColorCount() == ColorCount256 {
 		r0, g0, b0 := color256ToRGB(uint8(color.colorValue()))
 		return NewColor24Bit(r0, g0, b0)
 	}
 
-	panic(fmt.Errorf("unhandled color type %d", color.ColorType()))
+	panic(fmt.Errorf("unhandled color type %d", color.ColorCount()))
 }
 
-func (color Color) downsampleTo(terminalColorCount ColorType) Color {
-	if color.ColorType() == ColorTypeDefault || terminalColorCount == ColorTypeDefault {
+func (color Color) downsampleTo(terminalColorCount ColorCount) Color {
+	if color.ColorCount() == ColorCountDefault || terminalColorCount == ColorCountDefault {
 		panic(fmt.Errorf("downsampling to or from default color not supported, %s -> %#v", color.String(), terminalColorCount))
 	}
 
-	if color.ColorType() <= terminalColorCount {
+	if color.ColorCount() <= terminalColorCount {
 		// Already low enough
 		return color
 	}
@@ -192,13 +206,13 @@ func (color Color) downsampleTo(terminalColorCount ColorType) Color {
 	var scanFirst int
 	var scanLast int
 	switch terminalColorCount {
-	case ColorType8:
+	case ColorCount8:
 		scanFirst = 0
 		scanLast = 7
-	case ColorType16:
+	case ColorCount16:
 		scanFirst = 0
 		scanLast = 15
-	case ColorType256:
+	case ColorCount256:
 		// Colors 0-15 can be customized by the user, so we skip them and use
 		// only the well defined ones
 		scanFirst = 16
@@ -234,7 +248,7 @@ func (color Color) downsampleTo(terminalColorCount ColorType) Color {
 // The result from this function has been scaled to 0.0-1.0, where 1.0 is the
 // distance between black and white.
 func (color Color) Distance(other Color) float64 {
-	if color.ColorType() != ColorType24bit {
+	if color.ColorCount() != ColorCount24bit {
 		panic(fmt.Errorf("contrast only supported for 24 bit colors, got %s vs %s", color.String(), other.String()))
 	}
 

twin/colors_test.go

@@ -1,6 +1,7 @@
 package twin
 
 import (
+	"strings"
 	"testing"
 
 	"gotest.tools/v3/assert"
@@ -8,14 +9,14 @@ import (
 
 func TestDownsample24BitsTo16Colors(t *testing.T) {
 	assert.Equal(t,
-		NewColor24Bit(255, 255, 255).downsampleTo(ColorType16),
+		NewColor24Bit(255, 255, 255).downsampleTo(ColorCount16),
 		NewColor16(15),
 	)
 }
 
 func TestDownsample24BitsTo256Colors(t *testing.T) {
 	assert.Equal(t,
-		NewColor24Bit(255, 255, 255).downsampleTo(ColorType256),
+		NewColor24Bit(255, 255, 255).downsampleTo(ColorCount256),
 
 		// From https://jonasjacek.github.io/colors/
 		NewColor256(231),
@@ -24,22 +25,28 @@ func TestDownsample24BitsTo256Colors(t *testing.T) {
 
 func TestRealWorldDownsampling(t *testing.T) {
 	assert.Equal(t,
-		NewColor24Bit(0xd0, 0xd0, 0xd0).downsampleTo(ColorType256),
+		NewColor24Bit(0xd0, 0xd0, 0xd0).downsampleTo(ColorCount256),
 		NewColor256(252), // From https://jonasjacek.github.io/colors/
 	)
 }
 
 func TestAnsiStringWithDownSampling(t *testing.T) {
+	actual := NewColor24Bit(0xd0, 0xd0, 0xd0).ansiString(colorTypeForeground, ColorCount256)
+	actual = strings.ReplaceAll(actual, "\x1b", "ESC")
+	expected := "ESC[38;5;252m"
 	assert.Equal(t,
-		NewColor24Bit(0xd0, 0xd0, 0xd0).ansiString(true, ColorType256),
-		"\x1b[38;5;252m",
+		actual,
+		expected,
 	)
 }
 
 func TestAnsiStringDefault(t *testing.T) {
+	actual := ColorDefault.ansiString(colorTypeBackground, ColorCount16)
+	actual = strings.ReplaceAll(actual, "\x1b", "ESC")
+	expected := "ESC[49m"
 	assert.Equal(t,
-		ColorDefault.ansiString(true, ColorType16),
-		"\x1b[39m",
+		actual,
+		expected,
 	)
 }
 

twin/panicHandler.go

@@ -6,12 +6,13 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
-func panicHandler(goroutineName string, recoverResult any) {
+func panicHandler(goroutineName string, recoverResult any, stackTrace []byte) {
 	if recoverResult == nil {
 		return
 	}
 
 	log.WithFields(log.Fields{
-		"recoverResult": recoverResult,
+		"panic":      recoverResult,
+		"stackTrace": string(stackTrace),
 	}).Error("Goroutine panicked: " + goroutineName)
 }

twin/screen-setup.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"os"
 	"os/signal"
+	"runtime/debug"
 	"sync/atomic"
 	"syscall"
 
@@ -118,7 +119,7 @@ func (screen *UnixScreen) setupSigwinchNotification() {
 	signal.Notify(sigwinch, syscall.SIGWINCH)
 	go func() {
 		defer func() {
-			panicHandler("setupSigwinchNotification()/SIGWINCH", recover())
+			panicHandler("setupSigwinchNotification()/SIGWINCH", recover(), debug.Stack())
 		}()
 
 		for {

twin/screen-setup_test.go

@@ -6,6 +6,7 @@ package twin
 import (
 	"io"
 	"os"
+	"runtime/debug"
 	"testing"
 	"time"
 
@@ -32,7 +33,7 @@ func TestInterruptableReader_blockedOnReadImmediate(t *testing.T) {
 	readResultChan := make(chan readResult)
 	go func() {
 		defer func() {
-			panicHandler("TestInterruptableReader_blockedOnReadImmediate()", recover())
+			panicHandler("TestInterruptableReader_blockedOnReadImmediate()", recover(), debug.Stack())
 		}()
 
 		buffer := make([]byte, 1)

twin/screen.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"regexp"
+	"runtime/debug"
 	"strconv"
 	"strings"
 	"unicode/utf8"
@@ -96,7 +97,7 @@ type UnixScreen struct {
 	ttyOut        *os.File
 	oldTtyOutMode uint32 //nolint Windows only
 
-	terminalColorCount ColorType
+	terminalColorCount ColorCount
 }
 
 // Example event: "\x1b[<65;127;41M"
@@ -121,15 +122,15 @@ func NewScreen() (Screen, error) {
 }
 
 func NewScreenWithMouseMode(mouseMode MouseMode) (Screen, error) {
-	terminalColorCount := ColorType24bit
+	terminalColorCount := ColorCount24bit
 	if os.Getenv("COLORTERM") != "truecolor" && strings.Contains(os.Getenv("TERM"), "256") {
 		// Covers "xterm-256color" as used by the macOS Terminal
-		terminalColorCount = ColorType256
+		terminalColorCount = ColorCount256
 	}
-	return NewScreenWithMouseModeAndColorType(mouseMode, terminalColorCount)
+	return NewScreenWithMouseModeAndColorCount(mouseMode, terminalColorCount)
 }
 
-func NewScreenWithMouseModeAndColorType(mouseMode MouseMode, terminalColorCount ColorType) (Screen, error) {
+func NewScreenWithMouseModeAndColorCount(mouseMode MouseMode, terminalColorCount ColorCount) (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())
 	}
@@ -181,7 +182,7 @@ func NewScreenWithMouseModeAndColorType(mouseMode MouseMode, terminalColorCount
 
 	go func() {
 		defer func() {
-			panicHandler("NewScreenWithMouseModeAndColorType()/mainLoop()", recover())
+			panicHandler("NewScreenWithMouseModeAndColorCount()/mainLoop()", recover(), debug.Stack())
 		}()
 
 		screen.mainLoop()
@@ -413,7 +414,7 @@ func (screen *UnixScreen) mainLoop() {
 		}
 
 		// We only expect this on entry, it's requested right before we start
-		// the main loop in NewScreenWithMouseModeAndColorType().
+		// the main loop in NewScreenWithMouseModeAndColorCount().
 		expectingTerminalBackgroundColor = false
 
 		if count > maxBytesRead {
@@ -657,7 +658,7 @@ func (screen *UnixScreen) Clear() {
 
 // Returns the rendered line, plus how many information carrying cells went into
 // it
-func renderLine(row []Cell, terminalColorCount ColorType) (string, int) {
+func renderLine(row []Cell, terminalColorCount ColorCount) (string, int) {
 	// Strip trailing whitespace
 	lastSignificantCellIndex := len(row) - 1
 	for ; lastSignificantCellIndex >= 0; lastSignificantCellIndex-- {

twin/screen_test.go

@@ -3,6 +3,7 @@ package twin
 import (
 	"io"
 	"os"
+	"runtime/debug"
 	"strings"
 	"testing"
 	"time"
@@ -64,7 +65,7 @@ func TestRenderLine(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorType16)
+	rendered, count := renderLine(row, ColorCount16)
 	assert.Equal(t, count, 2)
 	reset := ""
 	reversed := ""
@@ -79,7 +80,7 @@ func TestRenderLine(t *testing.T) {
 func TestRenderLineEmpty(t *testing.T) {
 	row := []Cell{}
 
-	rendered, count := renderLine(row, ColorType16)
+	rendered, count := renderLine(row, ColorCount16)
 	assert.Equal(t, count, 0)
 
 	// All lines are expected to stand on their own, so we always need to clear
@@ -95,7 +96,7 @@ func TestRenderLineLastReversed(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorType16)
+	rendered, count := renderLine(row, ColorCount16)
 	assert.Equal(t, count, 1)
 	reset := ""
 	reversed := ""
@@ -113,7 +114,7 @@ func TestRenderLineLastNonSpace(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorType16)
+	rendered, count := renderLine(row, ColorCount16)
 	assert.Equal(t, count, 1)
 	reset := ""
 	clearToEol := ""
@@ -134,7 +135,7 @@ func TestRenderLineLastReversedPlusTrailingSpace(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorType16)
+	rendered, count := renderLine(row, ColorCount16)
 	assert.Equal(t, count, 1)
 	reset := ""
 	reversed := ""
@@ -156,7 +157,7 @@ func TestRenderLineOnlyTrailingSpaces(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorType16)
+	rendered, count := renderLine(row, ColorCount16)
 	assert.Equal(t, count, 0)
 
 	// All lines are expected to stand on their own, so we always need to clear
@@ -172,7 +173,7 @@ func TestRenderLineLastReversedSpaces(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorType16)
+	rendered, count := renderLine(row, ColorCount16)
 	assert.Equal(t, count, 1)
 	reset := ""
 	reversed := ""
@@ -189,7 +190,7 @@ func TestRenderLineNonPrintable(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorType16)
+	rendered, count := renderLine(row, ColorCount16)
 	assert.Equal(t, count, 1)
 	reset := ""
 	white := ""
@@ -210,7 +211,7 @@ func TestRenderHyperlinkAtEndOfLine(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorType16)
+	rendered, count := renderLine(row, ColorCount16)
 	assert.Equal(t, count, 1)
 
 	assert.Equal(t,
@@ -235,7 +236,7 @@ func TestMultiCharHyperlink(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorType16)
+	rendered, count := renderLine(row, ColorCount16)
 	assert.Equal(t, count, 3)
 
 	assert.Equal(t,
@@ -270,7 +271,7 @@ func TestInterruptableReader_blockedOnRead(t *testing.T) {
 	readResultChan := make(chan readResult)
 	go func() {
 		defer func() {
-			panicHandler("TestInterruptableReader_blockedOnRead()", recover())
+			panicHandler("TestInterruptableReader_blockedOnRead()", recover(), debug.Stack())
 		}()
 
 		buffer := make([]byte, 1)

twin/styles.go

@@ -19,9 +19,10 @@ const (
 )
 
 type Style struct {
-	fg    Color
-	bg    Color
-	attrs AttrMask
+	fg             Color
+	bg             Color
+	underlineColor Color
+	attrs          AttrMask
 
 	// This hyperlinkURL is a URL for in-terminal hyperlinks.
 	//
@@ -37,8 +38,13 @@ type Style struct {
 var StyleDefault Style
 
 func (style Style) String() string {
+	undelineSuffix := ""
+	if style.underlineColor != ColorDefault {
+		undelineSuffix = fmt.Sprintf(" underlined with %v", style.underlineColor)
+	}
+
 	if style.attrs == AttrNone {
-		return fmt.Sprint(style.fg, " on ", style.bg)
+		return fmt.Sprint(style.fg, " on ", style.bg, undelineSuffix)
 	}
 
 	attrNames := make([]string, 0)
@@ -67,15 +73,16 @@ func (style Style) String() string {
 		attrNames = append(attrNames, "\""+*style.hyperlinkURL+"\"")
 	}
 
-	return fmt.Sprint(strings.Join(attrNames, " "), " ", style.fg, " on ", style.bg)
+	return fmt.Sprint(strings.Join(attrNames, " "), " ", style.fg, " on ", style.bg, undelineSuffix)
 }
 
 func (style Style) WithAttr(attr AttrMask) Style {
 	result := Style{
-		fg:           style.fg,
-		bg:           style.bg,
-		attrs:        style.attrs | attr,
-		hyperlinkURL: style.hyperlinkURL,
+		fg:             style.fg,
+		bg:             style.bg,
+		underlineColor: style.underlineColor,
+		attrs:          style.attrs | attr,
+		hyperlinkURL:   style.hyperlinkURL,
 	}
 
 	// Bold and dim are mutually exclusive
@@ -97,19 +104,21 @@ func (style Style) WithHyperlink(hyperlinkURL *string) Style {
 	}
 
 	return Style{
-		fg:           style.fg,
-		bg:           style.bg,
-		attrs:        style.attrs,
-		hyperlinkURL: hyperlinkURL,
+		fg:             style.fg,
+		bg:             style.bg,
+		underlineColor: style.underlineColor,
+		attrs:          style.attrs,
+		hyperlinkURL:   hyperlinkURL,
 	}
 }
 
 func (style Style) WithoutAttr(attr AttrMask) Style {
 	return Style{
-		fg:           style.fg,
-		bg:           style.bg,
-		attrs:        style.attrs & ^attr,
-		hyperlinkURL: style.hyperlinkURL,
+		fg:             style.fg,
+		bg:             style.bg,
+		underlineColor: style.underlineColor,
+		attrs:          style.attrs & ^attr,
+		hyperlinkURL:   style.hyperlinkURL,
 	}
 }
 
@@ -119,19 +128,31 @@ func (attr AttrMask) has(attrs AttrMask) bool {
 
 func (style Style) WithBackground(color Color) Style {
 	return Style{
-		fg:           style.fg,
-		bg:           color,
-		attrs:        style.attrs,
-		hyperlinkURL: style.hyperlinkURL,
+		fg:             style.fg,
+		bg:             color,
+		underlineColor: style.underlineColor,
+		attrs:          style.attrs,
+		hyperlinkURL:   style.hyperlinkURL,
 	}
 }
 
 func (style Style) WithForeground(color Color) Style {
 	return Style{
-		fg:           color,
-		bg:           style.bg,
-		attrs:        style.attrs,
-		hyperlinkURL: style.hyperlinkURL,
+		fg:             color,
+		bg:             style.bg,
+		underlineColor: style.underlineColor,
+		attrs:          style.attrs,
+		hyperlinkURL:   style.hyperlinkURL,
+	}
+}
+
+func (style Style) WithUnderlineColor(color Color) Style {
+	return Style{
+		fg:             style.fg,
+		bg:             style.bg,
+		underlineColor: color,
+		attrs:          style.attrs,
+		hyperlinkURL:   style.hyperlinkURL,
 	}
 }
 
@@ -139,7 +160,7 @@ func (style Style) WithForeground(color Color) Style {
 // one.
 //
 //revive:disable-next-line:receiver-naming
-func (current Style) RenderUpdateFrom(previous Style, terminalColorCount ColorType) string {
+func (current Style) RenderUpdateFrom(previous Style, terminalColorCount ColorCount) string {
 	if current == previous {
 		// Shortcut for the common case
 		return ""
@@ -152,11 +173,15 @@ func (current Style) RenderUpdateFrom(previous Style, terminalColorCount ColorTy
 
 	var builder strings.Builder
 	if current.fg != previous.fg {
-		builder.WriteString(current.fg.ForegroundAnsiString(terminalColorCount))
+		builder.WriteString(current.fg.ansiString(colorTypeForeground, terminalColorCount))
 	}
 
 	if current.bg != previous.bg {
-		builder.WriteString(current.bg.BackgroundAnsiString(terminalColorCount))
+		builder.WriteString(current.bg.ansiString(colorTypeBackground, terminalColorCount))
+	}
+
+	if current.underlineColor != previous.underlineColor {
+		builder.WriteString(current.underlineColor.ansiString(colorTypeUnderline, terminalColorCount))
 	}
 
 	// Handle AttrDim / AttrBold changes

twin/styles_test.go

@@ -12,6 +12,6 @@ func TestHyperlinkToNormal(t *testing.T) {
 
 	style := StyleDefault.WithHyperlink(&url)
 	assert.Equal(t,
-		strings.ReplaceAll(StyleDefault.RenderUpdateFrom(style, ColorType16), "", "ESC"),
+		strings.ReplaceAll(StyleDefault.RenderUpdateFrom(style, ColorCount16), "", "ESC"),
 		"ESC]8;;ESC\\")
 }