Handle reading underline color

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)
 }
 

sample-files/colored-underlines.txt

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

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,
 	}
 }
 
@@ -159,6 +180,10 @@ func (current Style) RenderUpdateFrom(previous Style, terminalColorCount ColorCo
 		builder.WriteString(current.bg.ansiString(colorTypeBackground, terminalColorCount))
 	}
 
+	if current.underlineColor != previous.underlineColor {
+		builder.WriteString(current.underlineColor.ansiString(colorTypeUnderline, terminalColorCount))
+	}
+
 	// Handle AttrDim / AttrBold changes
 	previousBoldDim := previous.attrs & (AttrBold | AttrDim)
 	currentBoldDim := current.attrs & (AttrBold | AttrDim)