Support mode 2031 dark/light mode detection

Author: the-mikedavis

book/src/themes.md

@@ -2,6 +2,17 @@
 
 To use a theme add `theme = "<name>"` to the top of your [`config.toml`](./configuration.md) file, or select it during runtime using `:theme <name>`.
 
+Separate themes can be configured for light and dark modes. On terminals supporting [mode 2031 dark/light detection](https://github.com/contour-terminal/contour/blob/master/docs/vt-extensions/color-palette-update-notifications.md), the theme mode is detected from the terminal.
+
+```toml
+[theme]
+dark = "catppuccin_frappe"
+light = "catppuccin_latte"
+## Optional. Used if the terminal doesn't declare a preference.
+## Defaults to the theme set for `dark` if not specified.
+# fallback = "catppuccin_frappe"
+```
+
 ## Creating a theme
 
 Create a file with the name of your theme as the file name (i.e `mytheme.toml`) and place it in your `themes` directory (i.e `~/.config/helix/themes` or `%AppData%\helix\themes` on Windows). The directory might have to be created beforehand.

helix-term/src/application.rs

@@ -67,6 +67,8 @@ pub struct Application {
     signals: Signals,
     jobs: Jobs,
     lsp_progress: LspProgressMap,
+
+    theme_mode: Option<theme::Mode>,
 }
 
 #[cfg(feature = "integration")]
@@ -109,6 +111,7 @@ impl Application {
         #[cfg(feature = "integration")]
         let backend = TestBackend::new(120, 150);
 
+        let theme_mode = backend.get_theme_mode();
         let terminal = Terminal::new(backend)?;
         let area = terminal.size().expect("couldn't get terminal size");
         let mut compositor = Compositor::new(area);
@@ -127,6 +130,7 @@ impl Application {
             &mut editor,
             &config.load(),
             terminal.backend().supports_true_color(),
+            theme_mode,
         );
 
         let keys = Box::new(Map::new(Arc::clone(&config), |config: &Config| {
@@ -246,6 +250,7 @@ impl Application {
             signals,
             jobs: Jobs::new(),
             lsp_progress: LspProgressMap::new(),
+            theme_mode,
         };
 
         Ok(app)
@@ -404,6 +409,7 @@ impl Application {
                 &mut self.editor,
                 &default_config,
                 self.terminal.backend().supports_true_color(),
+                self.theme_mode,
             );
 
             // Re-parse any open documents with the new language config.
@@ -437,12 +443,18 @@ impl Application {
     }
 
     /// Load the theme set in configuration
-    fn load_configured_theme(editor: &mut Editor, config: &Config, terminal_true_color: bool) {
+    fn load_configured_theme(
+        editor: &mut Editor,
+        config: &Config,
+        terminal_true_color: bool,
+        mode: Option<theme::Mode>,
+    ) {
         let true_color = terminal_true_color || config.editor.true_color || crate::true_color();
         let theme = config
             .theme
             .as_ref()
-            .and_then(|theme| {
+            .and_then(|theme_config| {
+                let theme = theme_config.choose(mode);
                 editor
                     .theme_loader
                     .load(theme)
@@ -660,6 +672,8 @@ impl Application {
     }
 
     pub async fn handle_terminal_events(&mut self, event: std::io::Result<termina::Event>) {
+        use termina::escape::csi;
+
         let mut cx = crate::compositor::Context {
             editor: &mut self.editor,
             jobs: &mut self.jobs,
@@ -684,6 +698,15 @@ impl Application {
                 kind: termina::event::KeyEventKind::Release,
                 ..
             }) => false,
+            termina::Event::Csi(csi::Csi::Mode(csi::Mode::ReportTheme(mode))) => {
+                Self::load_configured_theme(
+                    &mut self.editor,
+                    &self.config.load(),
+                    self.terminal.backend().supports_true_color(),
+                    Some(mode.into()),
+                );
+                true
+            }
             event => self.compositor.handle_event(&event.into(), &mut cx),
         };
 
@@ -1134,9 +1157,16 @@ impl Application {
 
     #[cfg(not(feature = "integration"))]
     pub fn event_stream(&self) -> impl Stream<Item = std::io::Result<termina::Event>> + Unpin {
-        use termina::Terminal as _;
+        use termina::{escape::csi, Terminal as _};
         let reader = self.terminal.backend().terminal().event_reader();
-        termina::EventStream::new(reader, |event| !event.is_escape())
+        termina::EventStream::new(reader, |event| {
+            // Accept either non-escape sequences or theme mode updates.
+            !event.is_escape()
+                || matches!(
+                    event,
+                    termina::Event::Csi(csi::Csi::Mode(csi::Mode::ReportTheme(_)))
+                )
+        })
     }
 
     #[cfg(feature = "integration")]

helix-term/src/config.rs

@@ -1,7 +1,7 @@
 use crate::keymap;
 use crate::keymap::{merge_keys, KeyTrie};
 use helix_loader::merge_toml_values;
-use helix_view::document::Mode;
+use helix_view::{document::Mode, theme};
 use serde::Deserialize;
 use std::collections::HashMap;
 use std::fmt::Display;
@@ -11,15 +11,15 @@ use toml::de::Error as TomlError;
 
 #[derive(Debug, Clone, PartialEq)]
 pub struct Config {
-    pub theme: Option<String>,
+    pub theme: Option<theme::Config>,
     pub keys: HashMap<Mode, KeyTrie>,
     pub editor: helix_view::editor::Config,
 }
 
 #[derive(Debug, Clone, PartialEq, Deserialize)]
 #[serde(deny_unknown_fields)]
 pub struct ConfigRaw {
-    pub theme: Option<String>,
+    pub theme: Option<theme::Config>,
     pub keys: Option<HashMap<Mode, KeyTrie>>,
     pub editor: Option<toml::Value>,
 }

helix-tui/src/backend/mod.rs

@@ -39,4 +39,5 @@ pub trait Backend {
     /// Flushes the terminal buffer
     fn flush(&mut self) -> Result<(), io::Error>;
     fn supports_true_color(&self) -> bool;
+    fn get_theme_mode(&self) -> Option<helix_view::theme::Mode>;
 }

helix-tui/src/backend/termina.rs

@@ -3,7 +3,7 @@ use std::io::{self, Write as _};
 use helix_view::{
     editor::KittyKeyboardProtocolConfig,
     graphics::{CursorKind, Rect, UnderlineStyle},
-    theme::{Color, Modifier},
+    theme::{self, Color, Modifier},
 };
 use termina::{
     escape::{
@@ -52,6 +52,7 @@ struct Capabilities {
     synchronized_output: bool,
     true_color: bool,
     extended_underlines: bool,
+    theme_mode: Option<theme::Mode>,
 }
 
 #[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
@@ -148,11 +149,13 @@ impl TerminaBackend {
         // If we only receive the device attributes then we know it is not.
         write!(
             terminal,
-            "{}{}{}{}{}{}",
+            "{}{}{}{}{}{}{}",
             // Synchronized output
             Csi::Mode(csi::Mode::QueryDecPrivateMode(csi::DecPrivateMode::Code(
                 csi::DecPrivateModeCode::SynchronizedOutput
             ))),
+            // Mode 2031 theme updates. Query the current theme.
+            Csi::Mode(csi::Mode::QueryTheme),
             // True color and while we're at it, extended underlines:
             // <https://github.com/termstandard/colors?tab=readme-ov-file#querying-the-terminal>
             Csi::Sgr(csi::Sgr::Background(TEST_COLOR.into())),
@@ -184,6 +187,9 @@ impl TerminaBackend {
                     })) => {
                         capabilities.synchronized_output = true;
                     }
+                    Event::Csi(Csi::Mode(csi::Mode::ReportTheme(mode))) => {
+                        capabilities.theme_mode = Some(mode.into());
+                    }
                     Event::Dcs(dcs::Dcs::Response {
                         value: dcs::DcsResponse::GraphicRendition(sgrs),
                         ..
@@ -320,6 +326,11 @@ impl TerminaBackend {
             }
         }
 
+        if self.capabilities.theme_mode.is_some() {
+            // Enable mode 2031 theme mode notifications:
+            write!(self.terminal, "{}", decset!(Theme))?;
+        }
+
         Ok(())
     }
 
@@ -332,6 +343,11 @@ impl TerminaBackend {
             )?;
         }
 
+        if self.capabilities.theme_mode.is_some() {
+            // Mode 2031 theme notifications.
+            write!(self.terminal, "{}", decreset!(Theme))?;
+        }
+
         Ok(())
     }
 
@@ -550,6 +566,10 @@ impl Backend for TerminaBackend {
     fn supports_true_color(&self) -> bool {
         self.capabilities.true_color
     }
+
+    fn get_theme_mode(&self) -> Option<theme::Mode> {
+        self.capabilities.theme_mode
+    }
 }
 
 impl Drop for TerminaBackend {

helix-tui/src/backend/test.rs

@@ -160,4 +160,8 @@ impl Backend for TestBackend {
     fn supports_true_color(&self) -> bool {
         false
     }
+
+    fn get_theme_mode(&self) -> Option<helix_view::theme::Mode> {
+        None
+    }
 }

helix-view/src/theme.rs

@@ -35,6 +35,75 @@ pub static BASE16_DEFAULT_THEME: Lazy<Theme> = Lazy::new(|| Theme {
     ..Theme::from(BASE16_DEFAULT_THEME_DATA.clone())
 });
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum Mode {
+    Dark,
+    Light,
+}
+
+#[cfg(feature = "term")]
+impl From<termina::escape::csi::ThemeMode> for Mode {
+    fn from(mode: termina::escape::csi::ThemeMode) -> Self {
+        match mode {
+            termina::escape::csi::ThemeMode::Dark => Self::Dark,
+            termina::escape::csi::ThemeMode::Light => Self::Light,
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Config {
+    light: String,
+    dark: String,
+    /// A theme to choose when the terminal did not declare either light or dark mode.
+    /// When not specified the dark theme is preferred.
+    fallback: Option<String>,
+}
+
+impl Config {
+    pub fn choose(&self, preference: Option<Mode>) -> &str {
+        match preference {
+            Some(Mode::Light) => &self.light,
+            Some(Mode::Dark) => &self.dark,
+            None => self.fallback.as_ref().unwrap_or(&self.dark),
+        }
+    }
+}
+
+impl<'de> Deserialize<'de> for Config {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        #[derive(Deserialize)]
+        #[serde(untagged, deny_unknown_fields, rename_all = "kebab-case")]
+        enum InnerConfig {
+            Constant(String),
+            Adaptive {
+                dark: String,
+                light: String,
+                fallback: Option<String>,
+            },
+        }
+
+        let inner = InnerConfig::deserialize(deserializer)?;
+
+        let (light, dark, fallback) = match inner {
+            InnerConfig::Constant(theme) => (theme.clone(), theme.clone(), None),
+            InnerConfig::Adaptive {
+                light,
+                dark,
+                fallback,
+            } => (light, dark, fallback),
+        };
+
+        Ok(Self {
+            light,
+            dark,
+            fallback,
+        })
+    }
+}
 #[derive(Clone, Debug)]
 pub struct Loader {
     /// Theme directories to search from highest to lowest priority