feat(style): add underline style and color support

Add support to CSI 4:x and CSI 58 escape sequences

Ref: https://en.wikipedia.org/wiki/ANSI_escape_code#SGR
Ref: https://sw.kovidgoyal.net/kitty/underlines/

color.go

@@ -19,6 +19,8 @@ const (
 	ForegroudSeq = "38"
 	// Background sequence code.
 	BackgroundSeq = "48"
+	// Underline color sequence code.
+	UnderColorSeq = "58"
 )
 
 // Foreground and Background sequence codes

style.go

@@ -9,15 +9,20 @@ import (
 
 // Sequence definitions.
 const (
-	ResetSeq     = "0"
-	BoldSeq      = "1"
-	FaintSeq     = "2"
-	ItalicSeq    = "3"
-	UnderlineSeq = "4"
-	BlinkSeq     = "5"
-	ReverseSeq   = "7"
-	CrossOutSeq  = "9"
-	OverlineSeq  = "53"
+	ResetSeq       = "0"
+	BoldSeq        = "1"
+	FaintSeq       = "2"
+	ItalicSeq      = "3"
+	UnderlineSeq   = "4" // also 4:1
+	UnderdoubleSeq = "4:2"
+	UndercurlSeq   = "4:3"
+	UnderdotSeq    = "4:4"
+	UnderdashSeq   = "4:5"
+	BlinkSeq       = "5"
+	ReverseSeq     = "7"
+	CrossOutSeq    = "9"
+	OverlineSeq    = "53"
+	UndercolorSeq  = "58"
 )
 
 // Style is a string that various rendering styles can be applied to.
@@ -106,9 +111,63 @@ func (t Style) Italic() Style {
 	return t
 }
 
+func undercolorSeq(c Color) []string {
+	var seqs []string
+	switch v := c.(type) {
+	case NoColor:
+		return seqs
+	case ANSIColor:
+		// ANSIColor(s) are their own sequences.
+		// Underline colors don't support ANSI color sequences.
+		// Convert them into ANSI256
+		c = ANSI256Color(v.Color)
+	}
+	seqs = append(seqs, UndercolorSeq, c.Sequence())
+	return seqs
+}
+
 // Underline enables underline rendering.
-func (t Style) Underline() Style {
+func (t Style) Underline(c ...Color) Style {
 	t.styles = append(t.styles, UnderlineSeq)
+	if len(c) > 0 {
+		t.styles = append(t.styles, undercolorSeq(c[0])...)
+	}
+	return t
+}
+
+// Underdouble enables double underline rendering.
+func (t Style) Underdouble(c ...Color) Style {
+	t.styles = append(t.styles, UnderdoubleSeq)
+	if len(c) > 0 {
+		t.styles = append(t.styles, undercolorSeq(c[0])...)
+	}
+	return t
+}
+
+// Undercurl enables curly underline rendering.
+func (t Style) Undercurl(c ...Color) Style {
+	t.styles = append(t.styles, UndercurlSeq)
+	if len(c) > 0 {
+		t.styles = append(t.styles, undercolorSeq(c[0])...)
+	}
+	return t
+}
+
+// Underdot enables dotted underline rendering.
+func (t Style) Underdot(c ...Color) Style {
+	t.styles = append(t.styles, UnderdotSeq)
+	if len(c) > 0 {
+		t.styles = append(t.styles, undercolorSeq(c[0])...)
+	}
+	return t
+}
+
+// Underdash enables dashed underline rendering.
+func (t Style) Underdash(c ...Color) Style {
+	t.styles = append(t.styles, UnderdashSeq)
+	if len(c) > 0 {
+		t.styles = append(t.styles, undercolorSeq(c[0])...)
+	}
 	return t
 }
 

templatehelper.go

@@ -45,14 +45,29 @@ func TemplateFuncs(p Profile) template.FuncMap {
 
 			return s.String()
 		},
-		"Bold":      styleFunc(p, Style.Bold),
-		"Faint":     styleFunc(p, Style.Faint),
-		"Italic":    styleFunc(p, Style.Italic),
-		"Underline": styleFunc(p, Style.Underline),
-		"Overline":  styleFunc(p, Style.Overline),
-		"Blink":     styleFunc(p, Style.Blink),
-		"Reverse":   styleFunc(p, Style.Reverse),
-		"CrossOut":  styleFunc(p, Style.CrossOut),
+		"Bold":        styleFunc(p, Style.Bold),
+		"Faint":       styleFunc(p, Style.Faint),
+		"Italic":      styleFunc(p, Style.Italic),
+		"Overline":    styleFunc(p, Style.Overline),
+		"Blink":       styleFunc(p, Style.Blink),
+		"Reverse":     styleFunc(p, Style.Reverse),
+		"CrossOut":    styleFunc(p, Style.CrossOut),
+		"Underline":   styleUnderline(p, Style.Underline),
+		"Underdouble": styleUnderline(p, Style.Underdouble),
+		"Undercurl":   styleUnderline(p, Style.Undercurl),
+		"Underdot":    styleUnderline(p, Style.Underdot),
+		"Underdash":   styleUnderline(p, Style.Underdash),
+	}
+}
+
+func styleUnderline(p Profile, f func(Style, ...Color) Style) func(...interface{}) string {
+	return func(values ...interface{}) string {
+		if len(values) == 2 {
+			s := p.String(values[1].(string))
+			return f(s, p.Color(values[0].(string))).String()
+		}
+		s := p.String(values[0].(string))
+		return f(s).String()
 	}
 }
 
@@ -64,17 +79,21 @@ func styleFunc(p Profile, f func(Style) Style) func(...interface{}) string {
 }
 
 var noopTemplateFuncs = template.FuncMap{
-	"Color":      noColorFunc,
-	"Foreground": noColorFunc,
-	"Background": noColorFunc,
-	"Bold":       noStyleFunc,
-	"Faint":      noStyleFunc,
-	"Italic":     noStyleFunc,
-	"Underline":  noStyleFunc,
-	"Overline":   noStyleFunc,
-	"Blink":      noStyleFunc,
-	"Reverse":    noStyleFunc,
-	"CrossOut":   noStyleFunc,
+	"Color":       noColorFunc,
+	"Foreground":  noColorFunc,
+	"Background":  noColorFunc,
+	"Bold":        noStyleFunc,
+	"Faint":       noStyleFunc,
+	"Italic":      noStyleFunc,
+	"Overline":    noStyleFunc,
+	"Blink":       noStyleFunc,
+	"Reverse":     noStyleFunc,
+	"CrossOut":    noStyleFunc,
+	"Underline":   noUnderline,
+	"Underdouble": noUnderline,
+	"Undercurl":   noUnderline,
+	"Underdot":    noUnderline,
+	"Underdash":   noUnderline,
 }
 
 func noColorFunc(values ...interface{}) string {
@@ -84,3 +103,10 @@ func noColorFunc(values ...interface{}) string {
 func noStyleFunc(values ...interface{}) string {
 	return values[0].(string)
 }
+
+func noUnderline(values ...interface{}) string {
+	if len(values) == 2 {
+		return values[1].(string)
+	}
+	return values[0].(string)
+}

testdata/templatehelper.tpl

@@ -8,7 +8,13 @@ Plain
 {{ Faint "Faint" }}
 {{ Italic "Italic" }}
 {{ Underline "Underline" }}
+{{ Underline "#ff0000" "Red Underline" }}
+{{ Underdouble "Double Underline" }}
+{{ Undercurl "Undercurl" }}
+{{ Undercurl "#00ff00" "Green Undercurl" }}
+{{ Underdot "Dotted Underline" }}
+{{ Underdash "Dashed Underline" }}
 {{ Overline "Overline" }}
 {{ Blink "Blink" }}
 {{ Reverse "Reverse" }}
-{{ CrossOut "CrossOut" }}
+{{ CrossOut "CrossOut" }}

testdata/templatehelper_ansi.txt

@@ -8,7 +8,13 @@ Plain
 Faint
 Italic
 Underline
+Red Underline
+[4:2mDouble Underline
+[4:3mUndercurl
+[4:3;58;5;10mGreen Undercurl
+[4:4mDotted Underline
+[4:5mDashed Underline
 Overline
 Blink
 Reverse
-CrossOut
+CrossOut

testdata/templatehelper_ansi256.txt

@@ -8,7 +8,13 @@ Plain
 Faint
 Italic
 Underline
+Red Underline
+[4:2mDouble Underline
+[4:3mUndercurl
+[4:3;58;5;46mGreen Undercurl
+[4:4mDotted Underline
+[4:5mDashed Underline
 Overline
 Blink
 Reverse
-CrossOut
+CrossOut

testdata/templatehelper_ascii.txt

@@ -8,7 +8,13 @@ Bold
 Faint
 Italic
 Underline
+Red Underline
+Double Underline
+Undercurl
+Green Undercurl
+Dotted Underline
+Dashed Underline
 Overline
 Blink
 Reverse
-CrossOut
+CrossOut

testdata/templatehelper_truecolor.txt

@@ -8,7 +8,13 @@ Plain
 Faint
 Italic
 Underline
+Red Underline
+[4:2mDouble Underline
+[4:3mUndercurl
+[4:3;58;2;0;255;0mGreen Undercurl
+[4:4mDotted Underline
+[4:5mDashed Underline
 Overline
 Blink
 Reverse
-CrossOut
+CrossOut