Merge pull request #4061 from pascalkuthe/undercurl-modifier

Support different kinds of underline rendering (updated)

11 files changed, 307 insertions, 33 deletions

diff --git a/Cargo.lock b/Cargo.lock
index c45d8739..ec48c596 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -508,6 +508,7 @@ dependencies = [
  "helix-core",
  "helix-view",
  "serde",
+ "termini",
  "unicode-segmentation",
 ]
 
@@ -1101,6 +1102,15 @@ dependencies = [
 ]
 
 [[package]]
+name = "termini"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "394766021ef3dae8077f080518cdf5360831990f77f5708d5e3594c9b3efa2f9"
+dependencies = [
+ "dirs-next",
+]
+
+[[package]]
 name = "textwrap"
 version = "0.15.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/book/src/themes.md b/book/src/themes.md
index d1244596..392b5f8c 100644
--- a/book/src/themes.md
+++ b/book/src/themes.md
@@ -13,10 +13,10 @@ The default theme.toml can be found [here](https://github.com/helix-editor/helix
 Each line in the theme file is specified as below:
 
 ```toml
-key = { fg = "#ffffff", bg = "#000000", modifiers = ["bold", "italic"] }
+key = { fg = "#ffffff", bg = "#000000", underline = { color = "#ff0000", style = "curl"}, modifiers = ["bold", "italic"] }
 ```
 
-where `key` represents what you want to style, `fg` specifies the foreground color, `bg` the background color, and `modifiers` is a list of style modifiers. `bg` and `modifiers` can be omitted to defer to the defaults.
+where `key` represents what you want to style, `fg` specifies the foreground color, `bg` the background color, `underline` the underline `style`/`color`, and `modifiers` is a list of style modifiers. `bg`, `underline` and `modifiers` can be omitted to defer to the defaults.
 
 To specify only the foreground color:
 
@@ -77,17 +77,35 @@ The following values may be used as modifiers.
 
 Less common modifiers might not be supported by your terminal emulator.
 
+| Modifier             |
+| ---                  |
+| `bold`               |
+| `dim`                |
+| `italic`             |
+| `underlined`         |
+| `slow_blink`         |
+| `rapid_blink`        |
+| `reversed`           |
+| `hidden`             |
+| `crossed_out`        |
+
+> Note: The `underlined` modifier is deprecated and only available for backwards compatibility.
+> Its behavior is equivalent to setting `underline.style="line"`.
+
+### Underline Style
+
+One of the following values may be used as a value for `underline.style`. 
+
+Some styles might not be supported by your terminal emulator.
+
 | Modifier       |
 | ---            |
-| `bold`         |
-| `dim`          |
-| `italic`       |
-| `underlined`   |
-| `slow_blink`   |
-| `rapid_blink`  |
-| `reversed`     |
-| `hidden`       |
-| `crossed_out`  |
+| `line`         |
+| `curl`         |
+| `dashed`       |
+| `dot`          |
+| `double_line`  |
+
 
 ### Inheritance
 
diff --git a/helix-tui/Cargo.toml b/helix-tui/Cargo.toml
index b220c64f..a4a1c389 100644
--- a/helix-tui/Cargo.toml
+++ b/helix-tui/Cargo.toml
@@ -20,6 +20,7 @@ bitflags = "1.3"
 cassowary = "0.3"
 unicode-segmentation = "1.10"
 crossterm = { version = "0.25", optional = true }
+termini = "0.1"
 serde = { version = "1", "optional" = true, features = ["derive"]}
 helix-view = { version = "0.6", path = "../helix-view", features = ["term"] }
 helix-core = { version = "0.6", path = "../helix-core" }
diff --git a/helix-tui/src/backend/crossterm.rs b/helix-tui/src/backend/crossterm.rs
index eff098b3..7c7250fa 100644
--- a/helix-tui/src/backend/crossterm.rs
+++ b/helix-tui/src/backend/crossterm.rs
@@ -7,12 +7,45 @@ use crossterm::{
         SetForegroundColor,
     },
     terminal::{self, Clear, ClearType},
+    Command,
 };
-use helix_view::graphics::{Color, CursorKind, Modifier, Rect};
-use std::io::{self, Write};
+use helix_view::graphics::{Color, CursorKind, Modifier, Rect, UnderlineStyle};
+use std::{
+    fmt,
+    io::{self, Write},
+};
+fn vte_version() -> Option<usize> {
+    std::env::var("VTE_VERSION").ok()?.parse().ok()
+}
+
+/// Describes terminal capabilities like extended underline, truecolor, etc.
+#[derive(Copy, Clone, Debug, Default)]
+struct Capabilities {
+    /// Support for undercurled, underdashed, etc.
+    has_extended_underlines: bool,
+}
+
+impl Capabilities {
+    /// Detect capabilities from the terminfo database located based
+    /// on the $TERM environment variable. If detection fails, returns
+    /// a default value where no capability is supported.
+    pub fn from_env_or_default() -> Self {
+        match termini::TermInfo::from_env() {
+            Err(_) => Capabilities::default(),
+            Ok(t) => Capabilities {
+                // Smulx, VTE: https://unix.stackexchange.com/a/696253/246284
+                // Su (used by kitty): https://sw.kovidgoyal.net/kitty/underlines
+                has_extended_underlines: t.extended_cap("Smulx").is_some()
+                    || t.extended_cap("Su").is_some()
+                    || vte_version() >= Some(5102),
+            },
+        }
+    }
+}
 
 pub struct CrosstermBackend<W: Write> {
     buffer: W,
+    capabilities: Capabilities,
 }
 
 impl<W> CrosstermBackend<W>
@@ -20,7 +53,10 @@ where
     W: Write,
 {
     pub fn new(buffer: W) -> CrosstermBackend<W> {
-        CrosstermBackend { buffer }
+        CrosstermBackend {
+            buffer,
+            capabilities: Capabilities::from_env_or_default(),
+        }
     }
 }
 
@@ -47,6 +83,8 @@ where
     {
         let mut fg = Color::Reset;
         let mut bg = Color::Reset;
+        let mut underline_color = Color::Reset;
+        let mut underline_style = UnderlineStyle::Reset;
         let mut modifier = Modifier::empty();
         let mut last_pos: Option<(u16, u16)> = None;
         for (x, y, cell) in content {
@@ -74,11 +112,32 @@ where
                 bg = cell.bg;
             }
 
+            let mut new_underline_style = cell.underline_style;
+            if self.capabilities.has_extended_underlines {
+                if cell.underline_color != underline_color {
+                    let color = CColor::from(cell.underline_color);
+                    map_error(queue!(self.buffer, SetUnderlineColor(color)))?;
+                    underline_color = cell.underline_color;
+                }
+            } else {
+                match new_underline_style {
+                    UnderlineStyle::Reset | UnderlineStyle::Line => (),
+                    _ => new_underline_style = UnderlineStyle::Line,
+                }
+            }
+
+            if new_underline_style != underline_style {
+                let attr = CAttribute::from(new_underline_style);
+                map_error(queue!(self.buffer, SetAttribute(attr)))?;
+                underline_style = new_underline_style;
+            }
+
             map_error(queue!(self.buffer, Print(&cell.symbol)))?;
         }
 
         map_error(queue!(
             self.buffer,
+            SetUnderlineColor(CColor::Reset),
             SetForegroundColor(CColor::Reset),
             SetBackgroundColor(CColor::Reset),
             SetAttribute(CAttribute::Reset)
@@ -153,9 +212,6 @@ impl ModifierDiff {
         if removed.contains(Modifier::ITALIC) {
             map_error(queue!(w, SetAttribute(CAttribute::NoItalic)))?;
         }
-        if removed.contains(Modifier::UNDERLINED) {
-            map_error(queue!(w, SetAttribute(CAttribute::NoUnderline)))?;
-        }
         if removed.contains(Modifier::DIM) {
             map_error(queue!(w, SetAttribute(CAttribute::NormalIntensity)))?;
         }
@@ -176,9 +232,6 @@ impl ModifierDiff {
         if added.contains(Modifier::ITALIC) {
             map_error(queue!(w, SetAttribute(CAttribute::Italic)))?;
         }
-        if added.contains(Modifier::UNDERLINED) {
-            map_error(queue!(w, SetAttribute(CAttribute::Underlined)))?;
-        }
         if added.contains(Modifier::DIM) {
             map_error(queue!(w, SetAttribute(CAttribute::Dim)))?;
         }
@@ -195,3 +248,58 @@ impl ModifierDiff {
         Ok(())
     }
 }
+
+/// Crossterm uses semicolon as a seperator for colors
+/// this is actually not spec compliant (altough commonly supported)
+/// However the correct approach is to use colons as a seperator.
+/// This usually doesn't make a difference for emulators that do support colored underlines.
+/// However terminals that do not support colored underlines will ignore underlines colors with colons
+/// while escape sequences with semicolons are always processed which leads to weird visual artifacts.
+/// See [this nvim issue](https://github.com/neovim/neovim/issues/9270) for details
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct SetUnderlineColor(pub CColor);
+
+impl Command for SetUnderlineColor {
+    fn write_ansi(&self, f: &mut impl fmt::Write) -> fmt::Result {
+        let color = self.0;
+
+        if color == CColor::Reset {
+            write!(f, "\x1b[59m")?;
+            return Ok(());
+        }
+        f.write_str("\x1b[58:")?;
+
+        let res = match color {
+            CColor::Black => f.write_str("5:0"),
+            CColor::DarkGrey => f.write_str("5:8"),
+            CColor::Red => f.write_str("5:9"),
+            CColor::DarkRed => f.write_str("5:1"),
+            CColor::Green => f.write_str("5:10"),
+            CColor::DarkGreen => f.write_str("5:2"),
+            CColor::Yellow => f.write_str("5:11"),
+            CColor::DarkYellow => f.write_str("5:3"),
+            CColor::Blue => f.write_str("5:12"),
+            CColor::DarkBlue => f.write_str("5:4"),
+            CColor::Magenta => f.write_str("5:13"),
+            CColor::DarkMagenta => f.write_str("5:5"),
+            CColor::Cyan => f.write_str("5:14"),
+            CColor::DarkCyan => f.write_str("5:6"),
+            CColor::White => f.write_str("5:15"),
+            CColor::Grey => f.write_str("5:7"),
+            CColor::Rgb { r, g, b } => write!(f, "2::{}:{}:{}", r, g, b),
+            CColor::AnsiValue(val) => write!(f, "5:{}", val),
+            _ => Ok(()),
+        };
+        res?;
+        write!(f, "m")?;
+        Ok(())
+    }
+
+    #[cfg(windows)]
+    fn execute_winapi(&self) -> crossterm::Result<()> {
+        Err(std::io::Error::new(
+            std::io::ErrorKind::Other,
+            "SetUnderlineColor not supported by winapi.",
+        ))
+    }
+}
diff --git a/helix-tui/src/buffer.rs b/helix-tui/src/buffer.rs
index 21c53aad..424e6d32 100644
--- a/helix-tui/src/buffer.rs
+++ b/helix-tui/src/buffer.rs
@@ -3,7 +3,7 @@ use helix_core::unicode::width::UnicodeWidthStr;
 use std::cmp::min;
 use unicode_segmentation::UnicodeSegmentation;
 
-use helix_view::graphics::{Color, Modifier, Rect, Style};
+use helix_view::graphics::{Color, Modifier, Rect, Style, UnderlineStyle};
 
 /// A buffer cell
 #[derive(Debug, Clone, PartialEq)]
@@ -11,6 +11,8 @@ pub struct Cell {
     pub symbol: String,
     pub fg: Color,
     pub bg: Color,
+    pub underline_color: Color,
+    pub underline_style: UnderlineStyle,
     pub modifier: Modifier,
 }
 
@@ -44,6 +46,13 @@ impl Cell {
         if let Some(c) = style.bg {
             self.bg = c;
         }
+        if let Some(c) = style.underline_color {
+            self.underline_color = c;
+        }
+        if let Some(style) = style.underline_style {
+            self.underline_style = style;
+        }
+
         self.modifier.insert(style.add_modifier);
         self.modifier.remove(style.sub_modifier);
         self
@@ -53,6 +62,8 @@ impl Cell {
         Style::default()
             .fg(self.fg)
             .bg(self.bg)
+            .underline_color(self.underline_color)
+            .underline_style(self.underline_style)
             .add_modifier(self.modifier)
     }
 
@@ -61,6 +72,8 @@ impl Cell {
         self.symbol.push(' ');
         self.fg = Color::Reset;
         self.bg = Color::Reset;
+        self.underline_color = Color::Reset;
+        self.underline_style = UnderlineStyle::Reset;
         self.modifier = Modifier::empty();
     }
 }
@@ -71,6 +84,8 @@ impl Default for Cell {
             symbol: " ".into(),
             fg: Color::Reset,
             bg: Color::Reset,
+            underline_color: Color::Reset,
+            underline_style: UnderlineStyle::Reset,
             modifier: Modifier::empty(),
         }
     }
@@ -87,7 +102,7 @@ impl Default for Cell {
 ///
 /// ```
 /// use helix_tui::buffer::{Buffer, Cell};
-/// use helix_view::graphics::{Rect, Color, Style, Modifier};
+/// use helix_view::graphics::{Rect, Color, UnderlineStyle, Style, Modifier};
 ///
 /// let mut buf = Buffer::empty(Rect{x: 0, y: 0, width: 10, height: 5});
 /// buf[(0, 2)].set_symbol("x");
@@ -97,7 +112,9 @@ impl Default for Cell {
 ///     symbol: String::from("r"),
 ///     fg: Color::Red,
 ///     bg: Color::White,
-///     modifier: Modifier::empty()
+///     underline_color: Color::Reset,
+///     underline_style: UnderlineStyle::Reset,
+///     modifier: Modifier::empty(),
 /// });
 /// buf[(5, 0)].set_char('x');
 /// assert_eq!(buf[(5, 0)].symbol, "x");
diff --git a/helix-tui/src/text.rs b/helix-tui/src/text.rs
index 602090e5..1bfe5ee1 100644
--- a/helix-tui/src/text.rs
+++ b/helix-tui/src/text.rs
@@ -134,6 +134,8 @@ impl<'a> Span<'a> {
     ///             style: Style {
     ///                 fg: Some(Color::Yellow),
     ///                 bg: Some(Color::Black),
+    ///                 underline_color: None,
+    ///                 underline_style: None,
     ///                 add_modifier: Modifier::empty(),
     ///                 sub_modifier: Modifier::empty(),
     ///             },
@@ -143,6 +145,8 @@ impl<'a> Span<'a> {
     ///             style: Style {
     ///                 fg: Some(Color::Yellow),
     ///                 bg: Some(Color::Black),
+    ///                 underline_color: None,
+    ///                 underline_style: None,
     ///                 add_modifier: Modifier::empty(),
     ///                 sub_modifier: Modifier::empty(),
     ///             },
@@ -152,6 +156,8 @@ impl<'a> Span<'a> {
     ///             style: Style {
     ///                 fg: Some(Color::Yellow),
     ///                 bg: Some(Color::Black),
+    ///                 underline_color: None,
+    ///                 underline_style: None,
     ///                 add_modifier: Modifier::empty(),
     ///                 sub_modifier: Modifier::empty(),
     ///             },
@@ -161,6 +167,8 @@ impl<'a> Span<'a> {
     ///             style: Style {
     ///                 fg: Some(Color::Yellow),
     ///                 bg: Some(Color::Black),
+    ///                 underline_color: None,
+    ///                 underline_style: None,
     ///                 add_modifier: Modifier::empty(),
     ///                 sub_modifier: Modifier::empty(),
     ///             },
diff --git a/helix-view/src/graphics.rs b/helix-view/src/graphics.rs
index fb3c8b3f..4374a537 100644
--- a/helix-view/src/graphics.rs
+++ b/helix-view/src/graphics.rs
@@ -315,6 +315,44 @@ impl From<Color> for crossterm::style::Color {
     }
 }
 
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum UnderlineStyle {
+    Reset,
+    Line,
+    Curl,
+    Dotted,
+    Dashed,
+    DoubleLine,
+}
+
+impl FromStr for UnderlineStyle {
+    type Err = &'static str;
+
+    fn from_str(modifier: &str) -> Result<Self, Self::Err> {
+        match modifier {
+            "line" => Ok(Self::Line),
+            "curl" => Ok(Self::Curl),
+            "dotted" => Ok(Self::Dotted),
+            "dashed" => Ok(Self::Dashed),
+            "double_line" => Ok(Self::DoubleLine),
+            _ => Err("Invalid underline style"),
+        }
+    }
+}
+
+impl From<UnderlineStyle> for crossterm::style::Attribute {
+    fn from(style: UnderlineStyle) -> Self {
+        match style {
+            UnderlineStyle::Line => crossterm::style::Attribute::Underlined,
+            UnderlineStyle::Curl => crossterm::style::Attribute::Undercurled,
+            UnderlineStyle::Dotted => crossterm::style::Attribute::Underdotted,
+            UnderlineStyle::Dashed => crossterm::style::Attribute::Underdashed,
+            UnderlineStyle::DoubleLine => crossterm::style::Attribute::DoubleUnderlined,
+            UnderlineStyle::Reset => crossterm::style::Attribute::NoUnderline,
+        }
+    }
+}
+
 bitflags! {
     /// Modifier changes the way a piece of text is displayed.
     ///
@@ -332,7 +370,6 @@ bitflags! {
         const BOLD              = 0b0000_0000_0001;
         const DIM               = 0b0000_0000_0010;
         const ITALIC            = 0b0000_0000_0100;
-        const UNDERLINED        = 0b0000_0000_1000;
         const SLOW_BLINK        = 0b0000_0001_0000;
         const RAPID_BLINK       = 0b0000_0010_0000;
         const REVERSED          = 0b0000_0100_0000;
@@ -349,7 +386,6 @@ impl FromStr for Modifier {
             "bold" => Ok(Self::BOLD),
             "dim" => Ok(Self::DIM),
             "italic" => Ok(Self::ITALIC),
-            "underlined" => Ok(Self::UNDERLINED),
             "slow_blink" => Ok(Self::SLOW_BLINK),
             "rapid_blink" => Ok(Self::RAPID_BLINK),
             "reversed" => Ok(Self::REVERSED),
@@ -375,7 +411,7 @@ impl FromStr for Modifier {
 /// just S3.
 ///
 /// ```rust
-/// # use helix_view::graphics::{Rect, Color, Modifier, Style};
+/// # use helix_view::graphics::{Rect, Color, UnderlineStyle, Modifier, Style};
 /// # use helix_tui::buffer::Buffer;
 /// let styles = [
 ///     Style::default().fg(Color::Blue).add_modifier(Modifier::BOLD | Modifier::ITALIC),
@@ -391,6 +427,8 @@ impl FromStr for Modifier {
 ///         fg: Some(Color::Yellow),
 ///         bg: Some(Color::Red),
 ///         add_modifier: Modifier::BOLD,
+///         underline_color: Some(Color::Reset),
+///         underline_style: Some(UnderlineStyle::Reset),
 ///         sub_modifier: Modifier::empty(),
 ///     },
 ///     buffer[(0, 0)].style(),
@@ -401,7 +439,7 @@ impl FromStr for Modifier {
 /// reset all properties until that point use [`Style::reset`].
 ///
 /// ```
-/// # use helix_view::graphics::{Rect, Color, Modifier, Style};
+/// # use helix_view::graphics::{Rect, Color, UnderlineStyle, Modifier, Style};
 /// # use helix_tui::buffer::Buffer;
 /// let styles = [
 ///     Style::default().fg(Color::Blue).add_modifier(Modifier::BOLD | Modifier::ITALIC),
@@ -415,6 +453,8 @@ impl FromStr for Modifier {
 ///     Style {
 ///         fg: Some(Color::Yellow),
 ///         bg: Some(Color::Reset),
+///         underline_color: Some(Color::Reset),
+///         underline_style: Some(UnderlineStyle::Reset),
 ///         add_modifier: Modifier::empty(),
 ///         sub_modifier: Modifier::empty(),
 ///     },
@@ -426,6 +466,8 @@ impl FromStr for Modifier {
 pub struct Style {
     pub fg: Option<Color>,
     pub bg: Option<Color>,
+    pub underline_color: Option<Color>,
+    pub underline_style: Option<UnderlineStyle>,
     pub add_modifier: Modifier,
     pub sub_modifier: Modifier,
 }
@@ -435,6 +477,8 @@ impl Default for Style {
         Style {
             fg: None,
             bg: None,
+            underline_color: None,
+            underline_style: None,
             add_modifier: Modifier::empty(),
             sub_modifier: Modifier::empty(),
         }
@@ -447,6 +491,8 @@ impl Style {
         Style {
             fg: Some(Color::Reset),
             bg: Some(Color::Reset),
+            underline_color: None,
+            underline_style: None,
             add_modifier: Modifier::empty(),
             sub_modifier: Modifier::all(),
         }
@@ -482,6 +528,36 @@ impl Style {
         self
     }
 
+    /// Changes the underline color.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// # use helix_view::graphics::{Color, Style};
+    /// let style = Style::default().underline_color(Color::Blue);
+    /// let diff = Style::default().underline_color(Color::Red);
+    /// assert_eq!(style.patch(diff), Style::default().underline_color(Color::Red));
+    /// ```
+    pub fn underline_color(mut self, color: Color) -> Style {
+        self.underline_color = Some(color);
+        self
+    }
+
+    /// Changes the underline style.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// # use helix_view::graphics::{UnderlineStyle, Style};
+    /// let style = Style::default().underline_style(UnderlineStyle::Line);
+    /// let diff = Style::default().underline_style(UnderlineStyle::Curl);
+    /// assert_eq!(style.patch(diff), Style::default().underline_style(UnderlineStyle::Curl));
+    /// ```
+    pub fn underline_style(mut self, style: UnderlineStyle) -> Style {
+        self.underline_style = Some(style);
+        self
+    }
+
     /// Changes the text emphasis.
     ///
     /// When applied, it adds the given modifier to the `Style` modifiers.
@@ -538,6 +614,8 @@ impl Style {
     pub fn patch(mut self, other: Style) -> Style {
         self.fg = other.fg.or(self.fg);
         self.bg = other.bg.or(self.bg);
+        self.underline_color = other.underline_color.or(self.underline_color);
+        self.underline_style = other.underline_style.or(self.underline_style);
 
         self.add_modifier.remove(other.sub_modifier);
         self.add_modifier.insert(other.add_modifier);
diff --git a/helix-view/src/gutter.rs b/helix-view/src/gutter.rs
index ab0e2986..2c207d27 100644
--- a/helix-view/src/gutter.rs
+++ b/helix-view/src/gutter.rs
@@ -1,7 +1,7 @@
 use std::fmt::Write;
 
 use crate::{
-    graphics::{Color, Modifier, Style},
+    graphics::{Color, Style, UnderlineStyle},
     Document, Editor, Theme, View,
 };
 
@@ -147,7 +147,7 @@ pub fn breakpoints<'doc>(
             .find(|breakpoint| breakpoint.line == line)?;
 
         let mut style = if breakpoint.condition.is_some() && breakpoint.log_message.is_some() {
-            error.add_modifier(Modifier::UNDERLINED)
+            error.underline_style(UnderlineStyle::Line)
         } else if breakpoint.condition.is_some() {
             error
         } else if breakpoint.log_message.is_some() {
diff --git a/helix-view/src/theme.rs b/helix-view/src/theme.rs
index 8a1f8b7e..302844b7 100644
--- a/helix-view/src/theme.rs
+++ b/helix-view/src/theme.rs
@@ -11,6 +11,7 @@ use once_cell::sync::Lazy;
 use serde::{Deserialize, Deserializer};
 use toml::{map::Map, Value};
 
+use crate::graphics::UnderlineStyle;
 pub use crate::graphics::{Color, Modifier, Style};
 
 pub static DEFAULT_THEME: Lazy<Theme> = Lazy::new(|| {
@@ -378,19 +379,48 @@ impl ThemePalette {
             .ok_or(format!("Theme: invalid modifier: {}", value))
     }
 
+    pub fn parse_underline_style(value: &Value) -> Result<UnderlineStyle, String> {
+        value
+            .as_str()
+            .and_then(|s| s.parse().ok())
+            .ok_or(format!("Theme: invalid underline style: {}", value))
+    }
+
     pub fn parse_style(&self, style: &mut Style, value: Value) -> Result<(), String> {
         if let Value::Table(entries) = value {
-            for (name, value) in entries {
+            for (name, mut value) in entries {
                 match name.as_str() {
                     "fg" => *style = style.fg(self.parse_color(value)?),
                     "bg" => *style = style.bg(self.parse_color(value)?),
+                    "underline" => {
+                        let table = value
+                            .as_table_mut()
+                            .ok_or("Theme: underline must be table")?;
+                        if let Some(value) = table.remove("color") {
+                            *style = style.underline_color(self.parse_color(value)?);
+                        }
+                        if let Some(value) = table.remove("style") {
+                            *style = style.underline_style(Self::parse_underline_style(&value)?);
+                        }
+
+                        if let Some(attr) = table.keys().next() {
+                            return Err(format!("Theme: invalid underline attribute: {attr}"));
+                        }
+                    }
                     "modifiers" => {
                         let modifiers = value
                             .as_array()
                             .ok_or("Theme: modifiers should be an array")?;
 
                         for modifier in modifiers {
-                            *style = style.add_modifier(Self::parse_modifier(modifier)?);
+                            if modifier
+                                .as_str()
+                                .map_or(false, |modifier| modifier == "underlined")
+                            {
+                                *style = style.underline_style(UnderlineStyle::Line);
+                            } else {
+                                *style = style.add_modifier(Self::parse_modifier(modifier)?);
+                            }
                         }
                     }
                     _ => return Err(format!("Theme: invalid style attribute: {}", name)),
diff --git a/runtime/themes/dark_plus.toml b/runtime/themes/dark_plus.toml
index f99da4fb..fbb58e64 100644
--- a/runtime/themes/dark_plus.toml
+++ b/runtime/themes/dark_plus.toml
@@ -92,7 +92,8 @@
 "info" = { fg = "light_blue" }
 "hint" = { fg = "light_gray3" }
 
-diagnostic = { modifiers = ["underlined"] }
+"diagnostic.error".underline = { color = "red", style = "curl" }
+"diagnostic".underline = { color = "gold", style = "curl" }
 
 [palette]
 white = "#ffffff"
diff --git a/runtime/themes/onedark.toml b/runtime/themes/onedark.toml
index 1e7d9af1..c4a56b90 100644
--- a/runtime/themes/onedark.toml
+++ b/runtime/themes/onedark.toml
@@ -39,7 +39,10 @@
 "diff.delta" = "gold"
 "diff.minus" = "red"
 
-diagnostic = { modifiers = ["underlined"] }
+"diagnostic.info".underline = { color = "blue", style = "curl" } 
+"diagnostic.hint".underline = { color = "green", style = "curl" } 
+"diagnostic.warning".underline = { color = "yellow", style = "curl" } 
+"diagnostic.error".underline = { color = "red", style = "curl" } 
 "info" = { fg = "blue", modifiers = ["bold"] }
 "hint" = { fg = "green", modifiers = ["bold"] }
 "warning" = { fg = "yellow", modifiers = ["bold"] }