Add underline style variants and underline color support

Support double, curly, dotted, and dashed underline styles via --color
(e.g. underline-curly) and ANSI passthrough (SGR 4:N, 58, 59) with --ansi.

Close #4633
Close #4678

Thanks to @shtse8 for the test cases.

src/ansi.go

@@ -22,20 +22,21 @@ type url struct {
 type ansiState struct {
 	fg   tui.Color
 	bg   tui.Color
+	ul   tui.Color
 	attr tui.Attr
 	lbg  tui.Color
 	url  *url
 }
 
 func (s *ansiState) colored() bool {
-	return s.fg != -1 || s.bg != -1 || s.attr > 0 || s.lbg >= 0 || s.url != nil
+	return s.fg != -1 || s.bg != -1 || s.ul != -1 || s.attr > 0 || s.lbg >= 0 || s.url != nil
 }
 
 func (s *ansiState) equals(t *ansiState) bool {
 	if t == nil {
 		return !s.colored()
 	}
-	return s.fg == t.fg && s.bg == t.bg && s.attr == t.attr && s.lbg == t.lbg && s.url == t.url
+	return s.fg == t.fg && s.bg == t.bg && s.ul == t.ul && s.attr == t.attr && s.lbg == t.lbg && s.url == t.url
 }
 
 func (s *ansiState) ToString() string {
@@ -54,7 +55,18 @@ func (s *ansiState) ToString() string {
 		ret += "3;"
 	}
 	if s.attr&tui.Underline > 0 {
-		ret += "4;"
+		switch s.attr.UnderlineStyle() {
+		case tui.UlStyleDouble:
+			ret += "4:2;"
+		case tui.UlStyleCurly:
+			ret += "4:3;"
+		case tui.UlStyleDotted:
+			ret += "4:4;"
+		case tui.UlStyleDashed:
+			ret += "4:5;"
+		default:
+			ret += "4;"
+		}
 	}
 	if s.attr&tui.Blink > 0 {
 		ret += "5;"
@@ -66,6 +78,9 @@ func (s *ansiState) ToString() string {
 		ret += "9;"
 	}
 	ret += toAnsiString(s.fg, 30) + toAnsiString(s.bg, 40)
+	if s.ul != -1 {
+		ret += toAnsiStringUl(s.ul)
+	}
 
 	ret = "\x1b[" + strings.TrimSuffix(ret, ";") + "m"
 	if s.url != nil {
@@ -74,6 +89,20 @@ func (s *ansiState) ToString() string {
 	return ret
 }
 
+func toAnsiStringUl(color tui.Color) string {
+	col := int(color)
+	if col < 0 {
+		return ""
+	}
+	if col >= (1 << 24) {
+		r := strconv.Itoa((col >> 16) & 0xff)
+		g := strconv.Itoa((col >> 8) & 0xff)
+		b := strconv.Itoa(col & 0xff)
+		return "58;2;" + r + ";" + g + ";" + b + ";"
+	}
+	return "58;5;" + strconv.Itoa(col) + ";"
+}
+
 func toAnsiString(color tui.Color, offset int) string {
 	col := int(color)
 	ret := ""
@@ -338,15 +367,19 @@ func extractColor(str string, state *ansiState, proc func(string, *ansiState) bo
 	return trimmed, nil, state
 }
 
-func parseAnsiCode(s string) (int, string) {
+func parseAnsiCode(s string) (int, byte, string) {
 	var remaining string
-	var i int
-	// Faster than strings.IndexAny(";:")
-	i = strings.IndexByte(s, ';')
-	if i < 0 {
-		i = strings.IndexByte(s, ':')
+	var sep byte
+	// Find the first separator (either ; or :)
+	i := -1
+	for j := 0; j < len(s); j++ {
+		if s[j] == ';' || s[j] == ':' {
+			i = j
+			break
+		}
 	}
 	if i >= 0 {
+		sep = s[i]
 		remaining = s[i+1:]
 		s = s[:i]
 	}
@@ -358,14 +391,14 @@ func parseAnsiCode(s string) (int, string) {
 		for _, ch := range stringBytes(s) {
 			ch -= '0'
 			if ch > 9 {
-				return -1, remaining
+				return -1, sep, remaining
 			}
 			code = code*10 + int(ch)
 		}
-		return code, remaining
+		return code, sep, remaining
 	}
 
-	return -1, remaining
+	return -1, sep, remaining
 }
 
 func interpretCode(ansiCode string, prevState *ansiState) ansiState {
@@ -373,14 +406,14 @@ func interpretCode(ansiCode string, prevState *ansiState) ansiState {
 		if prevState != nil {
 			return *prevState
 		}
-		return ansiState{-1, -1, 0, -1, nil}
+		return ansiState{-1, -1, -1, 0, -1, nil}
 	}
 
 	var state ansiState
 	if prevState == nil {
-		state = ansiState{-1, -1, 0, -1, nil}
+		state = ansiState{-1, -1, -1, 0, -1, nil}
 	} else {
-		state = ansiState{prevState.fg, prevState.bg, prevState.attr, prevState.lbg, prevState.url}
+		state = ansiState{prevState.fg, prevState.bg, prevState.ul, prevState.attr, prevState.lbg, prevState.url}
 	}
 	if ansiCode[0] != '\x1b' || ansiCode[1] != '[' || ansiCode[len(ansiCode)-1] != 'm' {
 		if prevState != nil && (strings.HasSuffix(ansiCode, "0K") || strings.HasSuffix(ansiCode, "[K")) {
@@ -405,6 +438,7 @@ func interpretCode(ansiCode string, prevState *ansiState) ansiState {
 	reset := func() {
 		state.fg = -1
 		state.bg = -1
+		state.ul = -1
 		state.attr = 0
 	}
 
@@ -420,7 +454,8 @@ func interpretCode(ansiCode string, prevState *ansiState) ansiState {
 	count := 0
 	for len(ansiCode) != 0 {
 		var num int
-		if num, ansiCode = parseAnsiCode(ansiCode); num != -1 {
+		var sep byte
+		if num, sep, ansiCode = parseAnsiCode(ansiCode); num != -1 {
 			count++
 			switch state256 {
 			case 0:
@@ -431,10 +466,15 @@ func interpretCode(ansiCode string, prevState *ansiState) ansiState {
 				case 48:
 					ptr = &state.bg
 					state256++
+				case 58:
+					ptr = &state.ul
+					state256++
 				case 39:
 					state.fg = -1
 				case 49:
 					state.bg = -1
+				case 59:
+					state.ul = -1
 				case 1:
 					state.attr = state.attr | tui.Bold
 				case 2:
@@ -442,7 +482,30 @@ func interpretCode(ansiCode string, prevState *ansiState) ansiState {
 				case 3:
 					state.attr = state.attr | tui.Italic
 				case 4:
-					state.attr = state.attr | tui.Underline
+					if sep == ':' {
+						// SGR 4:N — underline style sub-parameter
+						var subNum int
+						subNum, _, ansiCode = parseAnsiCode(ansiCode)
+						state.attr = state.attr &^ tui.UnderlineStyleMask
+						switch subNum {
+						case 0:
+							state.attr = state.attr &^ tui.Underline
+						case 1:
+							state.attr = state.attr | tui.Underline
+						case 2:
+							state.attr = state.attr | tui.Underline | tui.UlStyleDouble
+						case 3:
+							state.attr = state.attr | tui.Underline | tui.UlStyleCurly
+						case 4:
+							state.attr = state.attr | tui.Underline | tui.UlStyleDotted
+						case 5:
+							state.attr = state.attr | tui.Underline | tui.UlStyleDashed
+						default:
+							state.attr = state.attr | tui.Underline
+						}
+					} else {
+						state.attr = state.attr | tui.Underline
+					}
 				case 5:
 					state.attr = state.attr | tui.Blink
 				case 7:
@@ -456,6 +519,7 @@ func interpretCode(ansiCode string, prevState *ansiState) ansiState {
 					state.attr = state.attr &^ tui.Italic
 				case 24: // tput rmul
 					state.attr = state.attr &^ tui.Underline
+					state.attr = state.attr &^ tui.UnderlineStyleMask
 				case 25:
 					state.attr = state.attr &^ tui.Blink
 				case 27: