feat(settings): add font ligature toggle (#38)

Co-authored-by: l0ng-ai <24760907+l0ng-ai@users.noreply.github.com>

src/core/config.rs

@@ -9,7 +9,7 @@ use std::collections::HashMap;
 use std::path::PathBuf;
 use std::sync::OnceLock;
 
-use gpui::{Global, Hsla, Rgba, rgb};
+use gpui::{FontFeatures, Global, Hsla, Rgba, rgb};
 use serde::{Deserialize, Serialize};
 
 /// Top-level configuration. Stored as a GPUI global so any view can read it.
@@ -26,6 +26,10 @@ pub struct Config {
     /// Optional distinct face for italic cells. `None` reuses `font_family` with a
     /// synthesized italic slant.
     pub font_family_italic: Option<String>,
+    /// Optional OpenType font features for terminal text. When absent, tty7 keeps
+    /// terminal-safe defaults and disables contextual ligatures; when present,
+    /// this map is passed through to gpui as-is (for example `{ "calt": true }`).
+    pub font_features: Option<FontFeatures>,
     /// Base font size in pixels.
     pub font_size: f32,
     /// Line height as a multiple of the font size (e.g. 1.35 → a 13px font gets
@@ -230,6 +234,7 @@ impl Default for Config {
             ],
             font_family_bold: None,
             font_family_italic: None,
+            font_features: None,
             font_size: 15.0,
             line_height: 1.4,
             theme: "light".to_string(),
@@ -667,6 +672,23 @@ mod tests {
         assert_eq!(color_or(&Some("#ffffff".to_string()), 0x000000), white);
     }
 
+    #[test]
+    fn font_features_are_optional_and_parse_as_gpui_features() {
+        let cfg: Config =
+            serde_json::from_str(r#"{"font_features":{"calt":true,"liga":1}}"#).unwrap();
+        let features = cfg.font_features.expect("font features should parse");
+        assert_eq!(features.is_calt_enabled(), Some(true));
+        assert!(
+            features
+                .tag_value_list()
+                .iter()
+                .any(|(tag, value)| tag == "liga" && *value == 1)
+        );
+
+        let default_cfg = Config::default();
+        assert!(default_cfg.font_features.is_none());
+    }
+
     #[test]
     fn ansi_color_overrides_parse_and_default_independently() {
         let cfg: Config =

src/terminal/element.rs

@@ -151,10 +151,13 @@ fn build_font(base: &Font, bold: bool, italic: bool) -> Font {
         FontStyle::Normal
     };
     // Batched runs shape several chars in one line, where a programming font's
-    // contextual ligatures (`calt`, e.g. Fira Code's "->") would fuse cells into
-    // one glyph and break `force_width`'s one-glyph-per-column snapping. A cell
-    // grid can't ligate — Zed's terminal disables the same feature.
-    f.features = gpui::FontFeatures::disable_ligatures();
+    // contextual ligatures (`calt`, e.g. Fira Code's "->") can fuse cells into
+    // one glyph and stress `force_width`'s one-glyph-per-column snapping. Keep
+    // the terminal-safe default unless the user explicitly configured OpenType
+    // features on the base font.
+    if f.features.tag_value_list().is_empty() {
+        f.features = gpui::FontFeatures::disable_ligatures();
+    }
     f
 }
 
@@ -1896,6 +1899,23 @@ mod tests {
         assert_eq!(seg_clip_width(true, 1, cell), px(20.));
     }
 
+    #[test]
+    fn build_font_disables_ligatures_unless_features_are_configured() {
+        let font = build_font(&gpui::font("Test"), false, false);
+        assert_eq!(font.features.is_calt_enabled(), Some(false));
+
+        let mut configured = gpui::font("Test");
+        configured.features = serde_json::from_str(r#"{"calt":true,"liga":1}"#).unwrap();
+        let font = build_font(&configured, false, false);
+        assert_eq!(font.features.is_calt_enabled(), Some(true));
+        assert!(
+            font.features
+                .tag_value_list()
+                .iter()
+                .any(|(tag, value)| tag == "liga" && *value == 1)
+        );
+    }
+
     #[test]
     fn segment_row_keeps_powerline_separators_solo() {
         // The native-draw intercept lives in the Solo arm of `paint_glyphs`;

src/terminal/view.rs

@@ -73,6 +73,9 @@ pub struct TerminalView {
     /// Optional distinct base face for italic cells (from `font_family_italic`).
     /// `None` → synthesize italic from `font`.
     pub font_italic: Option<Font>,
+    /// User-configured OpenType features for terminal fonts. `None` preserves
+    /// tty7's terminal-safe default (ligatures disabled); `Some` is opt-in.
+    font_features: Option<gpui::FontFeatures>,
     pub font_size: Pixels,
     /// Line height as a multiple of `font_size`; the element turns it into the
     /// concrete row height each frame. Sourced from `Config::line_height`.
@@ -438,14 +441,21 @@ impl TerminalView {
         let fallbacks = fallback_chain(&font_family, &config.font_fallbacks);
         let font_size = px(config.font_size);
         let line_height_mul = config.line_height;
+        let font_features = config.font_features.clone();
         let mut font = gpui::font(font_family);
         font.fallbacks = Some(gpui::FontFallbacks::from_fonts(fallbacks.clone()));
+        if let Some(features) = &font_features {
+            font.features = features.clone();
+        }
         // Optional distinct bold/italic faces, each carrying the same fallback
         // chain so glyph coverage matches the primary face.
         let alt_font = |family: &Option<String>| {
             family.as_ref().map(|f| {
                 let mut af = gpui::font(f.clone());
                 af.fallbacks = Some(gpui::FontFallbacks::from_fonts(fallbacks.clone()));
+                if let Some(features) = &font_features {
+                    af.features = features.clone();
+                }
                 af
             })
         };
@@ -591,6 +601,7 @@ impl TerminalView {
             font,
             font_bold,
             font_italic,
+            font_features,
             font_size,
             line_height_mul,
             cell_width: px(8.),
@@ -1647,6 +1658,9 @@ impl TerminalView {
         let fallbacks = self.font.fallbacks.clone();
         let mut font = gpui::font(family);
         font.fallbacks = fallbacks;
+        if let Some(features) = &self.font_features {
+            font.features = features.clone();
+        }
         self.font = font;
         cx.notify();
     }
@@ -1664,12 +1678,37 @@ impl TerminalView {
         cx.notify();
     }
 
+    /// Apply OpenType features to the live terminal fonts. `None` restores the
+    /// terminal-safe default path, where the renderer disables contextual
+    /// ligatures while building paint faces.
+    pub fn set_font_features(
+        &mut self,
+        features: Option<gpui::FontFeatures>,
+        cx: &mut Context<Self>,
+    ) {
+        self.font_features = features.clone();
+        let apply = |font: &mut Font| {
+            font.features = features.clone().unwrap_or_default();
+        };
+        apply(&mut self.font);
+        if let Some(font) = &mut self.font_bold {
+            apply(font);
+        }
+        if let Some(font) = &mut self.font_italic {
+            apply(font);
+        }
+        cx.notify();
+    }
+
     /// Build an alternate face from a family name, reusing the primary's
     /// fallbacks. `None` → `None` (fall back to synthesizing from `self.font`).
     fn alt_font(&self, family: Option<String>) -> Option<Font> {
         family.map(|f| {
             let mut af = gpui::font(f);
             af.fallbacks = self.font.fallbacks.clone();
+            if let Some(features) = &self.font_features {
+                af.features = features.clone();
+            }
             af
         })
     }

src/ui/app.rs

@@ -10,6 +10,7 @@ use gpui_component::input::{InputEvent, InputState};
 use gpui_component::select::{SearchableVec, SelectEvent, SelectState};
 use gpui_component::slider::{SliderEvent, SliderState};
 use gpui_component::{ActiveTheme as _, IndexPath, TitleBar};
+use std::sync::Arc;
 
 use crate::core::actions::*;
 use crate::core::config::{Config, NewTabPosition, ShellConfig, color_or, hsla_to_hex6};
@@ -100,6 +101,9 @@ pub struct Tty7App {
     /// tracked so the hot-reload observer can diff them like `font_family`.
     pub(crate) font_family_bold: Option<String>,
     pub(crate) font_family_italic: Option<String>,
+    /// Currently-applied OpenType features for terminal fonts. `None` means the
+    /// terminal-safe default (ligatures disabled).
+    pub(crate) font_features: Option<gpui::FontFeatures>,
     /// Keeps the `observe_global::<Config>` subscription alive for the app's
     /// lifetime so external edits to `config.json` (swapped in by the watcher in
     /// `main.rs`) live-apply font size / line height / family. Never read.
@@ -150,6 +154,7 @@ impl Tty7App {
         let font_family = cx.global::<Config>().font_family.clone();
         let font_family_bold = cx.global::<Config>().font_family_bold.clone();
         let font_family_italic = cx.global::<Config>().font_family_italic.clone();
+        let font_features = cx.global::<Config>().font_features.clone();
         // Live-apply hot-reloaded config: the watcher in `main.rs` swaps the
         // `Config` global on every `config.json` change, which fires this. Theme
         // and colors are handled separately by `apply_theme`; here we cover the
@@ -189,6 +194,7 @@ impl Tty7App {
             font_family,
             font_family_bold,
             font_family_italic,
+            font_features,
             _config_watch: config_watch,
             _keystroke_watch: keystroke_watch,
             palette: None,
@@ -545,6 +551,29 @@ impl Tty7App {
         cx.notify();
     }
 
+    /// Toggle terminal font ligatures through the generic `font_features`
+    /// config. On enables the common programming-font features; off restores
+    /// tty7's terminal-safe default (contextual ligatures disabled).
+    pub(crate) fn set_font_ligatures(&mut self, on: bool, cx: &mut Context<Self>) {
+        let features = on.then(|| {
+            gpui::FontFeatures(Arc::new(vec![
+                ("calt".to_string(), 1),
+                ("liga".to_string(), 1),
+            ]))
+        });
+        self.font_features = features.clone();
+        for tab in &self.tabs {
+            for leaf in tab.pane.leaves() {
+                let features = features.clone();
+                leaf.update(cx, |v, cx| v.set_font_features(features, cx));
+            }
+        }
+        let cfg = cx.global_mut::<Config>();
+        cfg.font_features = features;
+        cfg.save();
+        cx.notify();
+    }
+
     /// Apply a picked ANSI color override and re-paint the terminal palette live.
     /// `None` clears the slot back to the active preset's ANSI value.
     pub(crate) fn set_ansi_color_override(
@@ -1580,9 +1609,14 @@ impl Tty7App {
     /// writes it), and — because we never write the global or `save()` from here
     /// — closes the save → watch → reload loop that would otherwise oscillate.
     fn reload_from_config(&mut self, cx: &mut Context<Self>) {
-        let (font_size, line_height, font_family) = {
+        let (font_size, line_height, font_family, font_features) = {
             let cfg = cx.global::<Config>();
-            (cfg.font_size, cfg.line_height, cfg.font_family.clone())
+            (
+                cfg.font_size,
+                cfg.line_height,
+                cfg.font_family.clone(),
+                cfg.font_features.clone(),
+            )
         };
         if font_size != self.font_size {
             self.font_size = font_size;
@@ -1616,6 +1650,15 @@ impl Tty7App {
                 }
             }
         }
+        if font_features != self.font_features {
+            self.font_features = font_features.clone();
+            for tab in &self.tabs {
+                for leaf in tab.pane.leaves() {
+                    let features = font_features.clone();
+                    leaf.update(cx, |v, cx| v.set_font_features(features, cx));
+                }
+            }
+        }
         let (bold, italic) = {
             let cfg = cx.global::<Config>();
             (cfg.font_family_bold.clone(), cfg.font_family_italic.clone())

src/ui/settings.rs

@@ -504,6 +504,13 @@ impl Tty7App {
         let cfg = cx.global::<Config>();
         let cursor_style = cfg.cursor_style;
         let cursor_blink = cfg.cursor_blink;
+        let font_ligatures = cfg.font_features.as_ref().is_some_and(|features| {
+            features.is_calt_enabled() == Some(true)
+                || features
+                    .tag_value_list()
+                    .iter()
+                    .any(|(tag, value)| tag == "liga" && *value != 0)
+        });
         let colors = cfg.colors.clone();
         let ansi_colors = cfg.ansi_colors.clone();
 
@@ -614,6 +621,10 @@ impl Tty7App {
         let font_family_control = font_dropdown(&font_select);
         let font_bold_control = font_dropdown(&font_bold_select);
         let font_italic_control = font_dropdown(&font_italic_select);
+        let ligature_switch = Switch::new("font-ligatures")
+            .checked(font_ligatures)
+            .on_click(cx.listener(|this, on: &bool, _w, cx| this.set_font_ligatures(*on, cx)))
+            .into_any_element();
 
         let cursor_idx = match cursor_style {
             CursorStyle::Block => 0,
@@ -680,6 +691,12 @@ impl Tty7App {
                 font_italic_control,
                 cx,
             ))
+            .child(self.settings_row(
+                "Font ligatures",
+                "Enable common programming ligature features for terminal text.",
+                ligature_switch,
+                cx,
+            ))
             .child(self.section_rule(cx))
             .child(self.section_header("Cursor", cx))
             .child(self.settings_row(