Add Curly, Dotted, Dashed and colored underline concept to model

These aren't currently rendered, but the parser and model now support
recognizing expanded underline sequences:

```
CSI 24 m   -> No underline
CSI 4 m    -> Single underline
CSI 21 m   -> Double underline
CSI 60 m   -> Curly underline
CSI 61 m   -> Dotted underline
CSI 62 m   -> Dashed underline

CSI 58 ; 2 ; R ; G ; B m   -> set underline color to specified true color RGB
CSI 58 ; 5 ; I m           -> set underline color to palette index I (0-255)
CSI 59                     -> restore underline color to default
```

The Curly, Dotted and Dashed CSI codes are a wezterm assignment in the
SGR space.  This is by no means official; I just picked some numbers
that were not used based on the xterm ctrl sequences.

The color assignment codes 58 and 59 are prior art from Kitty.

refs: #415

term/src/terminalstate.rs

@@ -2514,6 +2514,9 @@ impl TerminalState {
             Sgr::Background(col) => {
                 self.pen.set_background(col);
             }
+            Sgr::UnderlineColor(col) => {
+                self.pen.set_underline_color(col);
+            }
             Sgr::Font(_) => {}
         }
     }

termwiz/src/cell.rs

@@ -56,6 +56,9 @@ struct FatAttributes {
     hyperlink: Option<Arc<Hyperlink>>,
     /// The image data, if any
     image: Option<Box<ImageCell>>,
+    /// The color of the underline.  If None, then
+    /// the foreground color is to be used
+    underline_color: ColorAttribute,
 }
 
 /// Define getter and setter for the attributes bitfield.
@@ -162,6 +165,12 @@ pub enum Underline {
     Single = 1,
     /// The cell is underlined with two lines
     Double = 2,
+    /// Curly underline
+    Curly = 3,
+    /// Dotted underline
+    Dotted = 4,
+    /// Dashed underline
+    Dashed = 5,
 }
 
 impl Default for Underline {
@@ -200,15 +209,15 @@ impl Into<bool> for Blink {
 
 impl CellAttributes {
     bitfield!(intensity, set_intensity, Intensity, 0b11, 0);
-    bitfield!(underline, set_underline, Underline, 0b11, 2);
-    bitfield!(blink, set_blink, Blink, 0b11, 4);
-    bitfield!(italic, set_italic, 6);
-    bitfield!(reverse, set_reverse, 7);
-    bitfield!(strikethrough, set_strikethrough, 8);
-    bitfield!(invisible, set_invisible, 9);
-    bitfield!(wrapped, set_wrapped, 10);
-    bitfield!(overline, set_overline, 11);
-    bitfield!(semantic_type, set_semantic_type, SemanticType, 0b11, 12);
+    bitfield!(underline, set_underline, Underline, 0b111, 2);
+    bitfield!(blink, set_blink, Blink, 0b11, 5);
+    bitfield!(italic, set_italic, 7);
+    bitfield!(reverse, set_reverse, 8);
+    bitfield!(strikethrough, set_strikethrough, 9);
+    bitfield!(invisible, set_invisible, 10);
+    bitfield!(wrapped, set_wrapped, 11);
+    bitfield!(overline, set_overline, 12);
+    bitfield!(semantic_type, set_semantic_type, SemanticType, 0b11, 13);
 
     /// Returns true if the attribute bits in both objects are equal.
     /// This can be used to cheaply test whether the styles of the two
@@ -233,6 +242,7 @@ impl CellAttributes {
             self.fat.replace(Box::new(FatAttributes {
                 hyperlink: None,
                 image: None,
+                underline_color: ColorAttribute::Default,
             }));
         }
     }
@@ -241,7 +251,11 @@ impl CellAttributes {
         let deallocate = self
             .fat
             .as_ref()
-            .map(|fat| fat.image.is_none() && fat.hyperlink.is_none())
+            .map(|fat| {
+                fat.image.is_none()
+                    && fat.hyperlink.is_none()
+                    && fat.underline_color == ColorAttribute::Default
+            })
             .unwrap_or(false);
         if deallocate {
             self.fat.take();
@@ -270,6 +284,21 @@ impl CellAttributes {
         }
     }
 
+    pub fn set_underline_color<C: Into<ColorAttribute>>(
+        &mut self,
+        underline_color: C,
+    ) -> &mut Self {
+        let underline_color = underline_color.into();
+        if underline_color == ColorAttribute::Default && self.fat.is_none() {
+            self
+        } else {
+            self.allocate_fat_attributes();
+            self.fat.as_mut().unwrap().underline_color = underline_color;
+            self.deallocate_fat_attributes_if_none();
+            self
+        }
+    }
+
     /// Clone the attributes, but exclude fancy extras such
     /// as hyperlinks or future sprite things
     pub fn clone_sgr_only(&self) -> Self {
@@ -284,6 +313,7 @@ impl CellAttributes {
         // be deterministically tagged as Output so that we have an
         // easier time in get_semantic_zones.
         res.set_semantic_type(SemanticType::default());
+        res.set_underline_color(self.underline_color());
         res
     }
 
@@ -296,6 +326,13 @@ impl CellAttributes {
             .as_ref()
             .and_then(|fat| fat.image.as_ref().map(|im| im.as_ref()))
     }
+
+    pub fn underline_color(&self) -> ColorAttribute {
+        self.fat
+            .as_ref()
+            .map(|fat| fat.underline_color)
+            .unwrap_or(ColorAttribute::Default)
+    }
 }
 
 #[cfg(feature = "use_serde")]

termwiz/src/escape/csi.rs

@@ -1086,6 +1086,7 @@ pub enum Sgr {
     /// Set the intensity/bold level
     Intensity(Intensity),
     Underline(Underline),
+    UnderlineColor(ColorSpec),
     Blink(Blink),
     Italic(bool),
     Inverse(bool),
@@ -1124,6 +1125,9 @@ impl Display for Sgr {
             Sgr::Intensity(Intensity::Normal) => code!(NormalIntensity),
             Sgr::Underline(Underline::Single) => code!(UnderlineOn),
             Sgr::Underline(Underline::Double) => code!(UnderlineDouble),
+            Sgr::Underline(Underline::Curly) => code!(UnderlineCurly),
+            Sgr::Underline(Underline::Dotted) => code!(UnderlineDotted),
+            Sgr::Underline(Underline::Dashed) => code!(UnderlineDashed),
             Sgr::Underline(Underline::None) => code!(UnderlineOff),
             Sgr::Blink(Blink::Slow) => code!(BlinkOn),
             Sgr::Blink(Blink::Rapid) => code!(RapidBlinkOn),
@@ -1213,6 +1217,18 @@ impl Display for Sgr {
                 c.green,
                 c.blue
             )?,
+            Sgr::UnderlineColor(ColorSpec::Default) => code!(ResetUnderlineColor),
+            Sgr::UnderlineColor(ColorSpec::TrueColor(c)) => write!(
+                f,
+                "{};2;{};{};{}m",
+                SgrCode::UnderlineColor as i64,
+                c.red,
+                c.green,
+                c.blue
+            )?,
+            Sgr::UnderlineColor(ColorSpec::PaletteIndex(idx)) => {
+                write!(f, "{};5;{}m", SgrCode::UnderlineColor as i64, *idx)?
+            }
         }
         Ok(())
     }
@@ -1814,7 +1830,14 @@ impl<'a> CSIParser<'a> {
                     SgrCode::NormalIntensity => one!(Sgr::Intensity(Intensity::Normal)),
                     SgrCode::UnderlineOn => one!(Sgr::Underline(Underline::Single)),
                     SgrCode::UnderlineDouble => one!(Sgr::Underline(Underline::Double)),
+                    SgrCode::UnderlineCurly => one!(Sgr::Underline(Underline::Curly)),
+                    SgrCode::UnderlineDotted => one!(Sgr::Underline(Underline::Dotted)),
+                    SgrCode::UnderlineDashed => one!(Sgr::Underline(Underline::Dashed)),
                     SgrCode::UnderlineOff => one!(Sgr::Underline(Underline::None)),
+                    SgrCode::UnderlineColor => {
+                        self.parse_sgr_color(params).map(Sgr::UnderlineColor)
+                    }
+                    SgrCode::ResetUnderlineColor => one!(Sgr::UnderlineColor(ColorSpec::default())),
                     SgrCode::BlinkOn => one!(Sgr::Blink(Blink::Slow)),
                     SgrCode::RapidBlinkOn => one!(Sgr::Blink(Blink::Rapid)),
                     SgrCode::BlinkOff => one!(Sgr::Blink(Blink::None)),
@@ -1948,6 +1971,12 @@ pub enum SgrCode {
     OverlineOn = 53,
     OverlineOff = 55,
 
+    UnderlineColor = 58,
+    ResetUnderlineColor = 59,
+    UnderlineCurly = 60,
+    UnderlineDotted = 61,
+    UnderlineDashed = 62,
+
     ForegroundBrightBlack = 90,
     ForegroundBrightRed = 91,
     ForegroundBrightGreen = 92,
@@ -2073,6 +2102,50 @@ mod test {
         );
     }
 
+    #[test]
+    fn underlines() {
+        assert_eq!(
+            parse('m', &[21], "\x1b[21m"),
+            vec![CSI::Sgr(Sgr::Underline(Underline::Double))]
+        );
+        assert_eq!(
+            parse('m', &[4], "\x1b[4m"),
+            vec![CSI::Sgr(Sgr::Underline(Underline::Single))]
+        );
+    }
+
+    #[test]
+    fn underline_color() {
+        assert_eq!(
+            parse('m', &[58, 2], "\x1b[58;2m"),
+            vec![CSI::Unspecified(Box::new(Unspecified {
+                params: [58, 2].to_vec(),
+                intermediates: vec![],
+                ignored_extra_intermediates: false,
+                control: 'm',
+            }))]
+        );
+
+        assert_eq!(
+            parse('m', &[58, 2, 255, 255, 255], "\x1b[58;2;255;255;255m"),
+            vec![CSI::Sgr(Sgr::UnderlineColor(ColorSpec::TrueColor(
+                RgbColor::new(255, 255, 255),
+            )))]
+        );
+        assert_eq!(
+            parse('m', &[58, 5, 220, 255, 255], "\x1b[58;5;220m\x1b[255;255m"),
+            vec![
+                CSI::Sgr(Sgr::UnderlineColor(ColorSpec::PaletteIndex(220))),
+                CSI::Unspecified(Box::new(Unspecified {
+                    params: [255, 255].to_vec(),
+                    intermediates: vec![],
+                    ignored_extra_intermediates: false,
+                    control: 'm',
+                })),
+            ]
+        );
+    }
+
     #[test]
     fn color() {
         assert_eq!(

termwiz/src/escape/parser/mod.rs

@@ -418,7 +418,7 @@ impl SixelBuilder {
 #[cfg(test)]
 mod test {
     use super::*;
-    use crate::cell::Intensity;
+    use crate::cell::{Intensity, Underline};
     use crate::escape::csi::Sgr;
     use crate::escape::EscCode;
     use std::io::Write;
@@ -478,6 +478,35 @@ mod test {
         assert_eq!(encode(&actions), "\x1b[1m\x1b[3mb");
     }
 
+    #[test]
+    fn fancy_underline() {
+        let mut p = Parser::new();
+
+        // Kitty underline sequences use a `:` which is explicitly invalid
+        // and deleted by the dec/ansi vtparser
+        let actions = p.parse_as_vec(b"\x1b[4:0mb");
+        assert_eq!(
+            vec![
+                // NO: Action::CSI(CSI::Sgr(Sgr::Underline(Underline::None))),
+                Action::Print('b'),
+            ],
+            actions
+        );
+
+        let actions = p.parse_as_vec(b"\x1b[60;61;62mb");
+        assert_eq!(
+            vec![
+                Action::CSI(CSI::Sgr(Sgr::Underline(Underline::Curly))),
+                Action::CSI(CSI::Sgr(Sgr::Underline(Underline::Dotted))),
+                Action::CSI(CSI::Sgr(Sgr::Underline(Underline::Dashed))),
+                Action::Print('b'),
+            ],
+            actions
+        );
+
+        assert_eq!(encode(&actions), "\x1b[60m\x1b[61m\x1b[62mb");
+    }
+
     #[test]
     fn basic_osc() {
         let mut p = Parser::new();

vtparse/src/lib.rs

@@ -707,6 +707,28 @@ mod test {
         );
     }
 
+    #[test]
+    fn test_fancy_underline() {
+        assert_eq!(
+            parse_as_vec(b"\x1b[4m"),
+            vec![VTAction::CsiDispatch {
+                params: vec![4],
+                intermediates: b"".to_vec(),
+                ignored_excess_intermediates: false,
+                byte: b'm'
+            }]
+        );
+
+        assert_eq!(
+            // This is the kitty curly underline sequence.
+            // The : is explicitly set to be ignored by
+            // the state machine tables, so this whole sequence
+            // is discarded during parsing.
+            parse_as_vec(b"\x1b[4:3m"),
+            vec![]
+        );
+    }
+
     #[test]
     fn test_csi_omitted_param() {
         assert_eq!(

wezterm-gui/src/gui/utilsprites.rs

@@ -369,6 +369,12 @@ impl<T: Texture2d> UtilSprites<T> {
             (false, true, Underline::None, true) => &self.strike_over,
             (false, true, Underline::Single, true) => &self.single_strike_over,
             (false, true, Underline::Double, true) => &self.double_strike_over,
+
+            // FIXME: these are just placeholders under we render
+            // these things properly
+            (_, _, Underline::Curly, _) => &self.double_underline,
+            (_, _, Underline::Dotted, _) => &self.double_underline,
+            (_, _, Underline::Dashed, _) => &self.double_underline,
         }
     }