feat: adaptive theme selection based on the terminal color scheme

Cargo.lock

@@ -1459,6 +1459,7 @@ dependencies = [
  "serde_json",
  "slotmap",
  "tempfile",
+ "terminal-colorsaurus",
  "thiserror 2.0.3",
  "tokio",
  "tokio-stream",
@@ -2376,6 +2377,31 @@ dependencies = [
  "windows-sys 0.59.0",
 ]
 
+[[package]]
+name = "terminal-colorsaurus"
+version = "0.4.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7778d24b27585f6f92ec5d2705e7cf1710fd0ffa43262c807dfb49fa53471e95"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "memchr",
+ "mio",
+ "terminal-trx",
+ "windows-sys 0.59.0",
+]
+
+[[package]]
+name = "terminal-trx"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "57a5b836e7f4f81afe61b5cd399eee774f25edcfd47009a76e29f53bb6487833"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "windows-sys 0.59.0",
+]
+
 [[package]]
 name = "termini"
 version = "1.0.0"

book/src/configuration.md

@@ -11,6 +11,8 @@ # Configuration
 
 ```toml
 theme = "onedark"
+# Adaptive Theme
+# theme = { light = "onelight", dark = "onedark" }
 
 [editor]
 line-number = "relative"

book/src/themes.md

@@ -1,6 +1,7 @@
 ## Themes
 
 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>`.
+Alternatively, `theme = { light = "<name>", dark = "<name>" }` tries to select a theme based on the terminal color scheme. The detection should work with all major terminals including Windows Terminal (starting with v1.22).
 
 ## Creating a theme
 

helix-term/src/application.rs

@@ -113,6 +113,7 @@ pub fn new(args: Args, config: Config, lang_loader: syntax::Loader) -> Result<Se
         let theme = config
             .theme
             .as_ref()
+            .map(helix_view::theme::Config::get_active_theme)
             .and_then(|theme| {
                 theme_loader
                     .load(theme)
@@ -428,6 +429,7 @@ fn refresh_theme(&mut self, config: &Config) -> Result<(), Error> {
         let theme = config
             .theme
             .as_ref()
+            .map(helix_view::theme::Config::get_active_theme)
             .and_then(|theme| {
                 self.theme_loader
                     .load(theme)

helix-term/src/config.rs

@@ -11,7 +11,7 @@
 
 #[derive(Debug, Clone, PartialEq)]
 pub struct Config {
-    pub theme: Option<String>,
+    pub theme: Option<helix_view::theme::Config>,
     pub keys: HashMap<Mode, KeyTrie>,
     pub editor: helix_view::editor::Config,
 }
@@ -19,7 +19,7 @@ pub struct Config {
 #[derive(Debug, Clone, PartialEq, Deserialize)]
 #[serde(deny_unknown_fields)]
 pub struct ConfigRaw {
-    pub theme: Option<String>,
+    pub theme: Option<helix_view::theme::Config>,
     pub keys: Option<HashMap<Mode, KeyTrie>>,
     pub editor: Option<toml::Value>,
 }

helix-view/Cargo.toml

@@ -27,6 +27,7 @@ helix-vcs = { path = "../helix-vcs" }
 bitflags = "2.6"
 anyhow = "1"
 crossterm = { version = "0.28", optional = true }
+terminal-colorsaurus = "0.4"
 
 tempfile = "3.14"
 

helix-view/src/theme.rs

@@ -9,7 +9,7 @@
 use helix_loader::merge_toml_values;
 use log::warn;
 use once_cell::sync::Lazy;
-use serde::{Deserialize, Deserializer};
+use serde::{Deserialize, Deserializer, Serialize};
 use toml::{map::Map, Value};
 
 use crate::graphics::UnderlineStyle;
@@ -540,6 +540,28 @@ fn try_from(value: Value) -> Result<Self, Self::Error> {
     }
 }
 
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(untagged, deny_unknown_fields)]
+pub enum Config {
+    Static(String),
+    Adaptive { light: String, dark: String },
+}
+
+impl Config {
+    pub fn get_active_theme(&self) -> &str {
+        match self {
+            Config::Static(x) => x,
+            Config::Adaptive { light, dark } => {
+                use terminal_colorsaurus::{color_scheme, ColorScheme, QueryOptions};
+                match color_scheme(QueryOptions::default()).unwrap_or(ColorScheme::Dark) {
+                    ColorScheme::Light => light,
+                    ColorScheme::Dark => dark,
+                }
+            }
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;