Load alt default theme if true color is not supported

book/src/configuration.md

@@ -23,6 +23,7 @@ To override global configuration parameters, create a `config.toml` file located
 | `idle-timeout` | Time in milliseconds since last keypress before idle timers trigger. Used for autocompletion, set to 0 for instant. | `400` |
 | `completion-trigger-len` | The min-length of word under cursor to trigger autocompletion | `2` |
 | `auto-info` | Whether to display infoboxes | `true` |
+| `true-color` | Set to `true` to override automatic detection of terminal truecolor support in the event of a false negative. | `false` |
 
 `[editor.filepicker]` section of the config. Sets options for file picker and global search. All but the last key listed in the default file-picker configuration below are IgnoreOptions: whether hidden files and files listed within ignore files are ignored by (not visible in) the helix file picker and global search. There is also one other key, `max-depth` available, which is not defined by default.
 

helix-term/src/application.rs

@@ -76,17 +76,27 @@ impl Application {
             None => Ok(def_lang_conf),
         };
 
-        let theme = if let Some(theme) = &config.theme {
-            match theme_loader.load(theme) {
-                Ok(theme) => theme,
-                Err(e) => {
-                    log::warn!("failed to load theme `{}` - {}", theme, e);
+        let true_color = config.editor.true_color || crate::true_color();
+        let theme = config
+            .theme
+            .as_ref()
+            .and_then(|theme| {
+                theme_loader
+                    .load(theme)
+                    .map_err(|e| {
+                        log::warn!("failed to load theme `{}` - {}", theme, e);
+                        e
+                    })
+                    .ok()
+                    .filter(|theme| (true_color || theme.is_16_color()))
+            })
+            .unwrap_or_else(|| {
+                if true_color {
                     theme_loader.default()
+                } else {
+                    theme_loader.base16_default()
                 }
-            }
-        } else {
-            theme_loader.default()
-        };
+            });
 
         let syn_loader_conf: helix_core::syntax::Configuration = lang_conf
             .and_then(|conf| conf.try_into())

helix-term/src/commands.rs

@@ -2236,8 +2236,18 @@ mod cmd {
         args: &[&str],
         _event: PromptEvent,
     ) -> anyhow::Result<()> {
-        let theme = args.first().context("theme not provided")?;
-        cx.editor.set_theme_from_name(theme)
+        let theme = args.first().context("Theme not provided")?;
+        let theme = cx
+            .editor
+            .theme_loader
+            .load(theme)
+            .with_context(|| format!("Failed setting theme {}", theme))?;
+        let true_color = cx.editor.config.true_color || crate::true_color();
+        if !(true_color || theme.is_16_color()) {
+            bail!("Unsupported theme: theme requires true color support");
+        }
+        cx.editor.set_theme(theme);
+        Ok(())
     }
 
     fn yank_main_selection_to_clipboard(

helix-term/src/lib.rs

@@ -9,3 +9,9 @@ pub mod config;
 pub mod job;
 pub mod keymap;
 pub mod ui;
+
+fn true_color() -> bool {
+    std::env::var("COLORTERM")
+        .map(|v| matches!(v.as_str(), "truecolor" | "24bit"))
+        .unwrap_or(false)
+}

helix-term/src/ui/mod.rs

@@ -186,6 +186,7 @@ pub mod completers {
             &helix_core::config_dir().join("themes"),
         ));
         names.push("default".into());
+        names.push("base16_default".into());
 
         let mut names: Vec<_> = names
             .into_iter()

helix-view/src/editor.rs

@@ -103,6 +103,8 @@ pub struct Config {
     /// Whether to display infoboxes. Defaults to true.
     pub auto_info: bool,
     pub file_picker: FilePickerConfig,
+    /// Set to `true` to override automatic detection of terminal truecolor support in the event of a false negative. Defaults to `false`.
+    pub true_color: bool,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
@@ -135,6 +137,7 @@ impl Default for Config {
             completion_trigger_len: 2,
             auto_info: true,
             file_picker: FilePickerConfig::default(),
+            true_color: false,
         }
     }
 }
@@ -261,16 +264,6 @@ impl Editor {
         self._refresh();
     }
 
-    pub fn set_theme_from_name(&mut self, theme: &str) -> anyhow::Result<()> {
-        use anyhow::Context;
-        let theme = self
-            .theme_loader
-            .load(theme.as_ref())
-            .with_context(|| format!("failed setting theme `{}`", theme))?;
-        self.set_theme(theme);
-        Ok(())
-    }
-
     fn _refresh(&mut self) {
         for (view, _) in self.tree.views_mut() {
             let doc = &self.documents[&view.doc];

helix-view/src/theme.rs

@@ -15,6 +15,10 @@ pub use crate::graphics::{Color, Modifier, Style};
 pub static DEFAULT_THEME: Lazy<Theme> = Lazy::new(|| {
     toml::from_slice(include_bytes!("../../theme.toml")).expect("Failed to parse default theme")
 });
+pub static BASE16_DEFAULT_THEME: Lazy<Theme> = Lazy::new(|| {
+    toml::from_slice(include_bytes!("../../base16_tty.toml"))
+        .expect("Failed to parse base 16 default theme")
+});
 
 #[derive(Clone, Debug)]
 pub struct Loader {
@@ -35,6 +39,9 @@ impl Loader {
         if name == "default" {
             return Ok(self.default());
         }
+        if name == "base16_default" {
+            return Ok(self.base16_default());
+        }
         let filename = format!("{}.toml", name);
 
         let user_path = self.user_dir.join(&filename);
@@ -74,6 +81,11 @@ impl Loader {
     pub fn default(&self) -> Theme {
         DEFAULT_THEME.clone()
     }
+
+    /// Returns the alternative 16-color default theme
+    pub fn base16_default(&self) -> Theme {
+        BASE16_DEFAULT_THEME.clone()
+    }
 }
 
 #[derive(Clone, Debug)]
@@ -134,6 +146,14 @@ impl Theme {
     pub fn find_scope_index(&self, scope: &str) -> Option<usize> {
         self.scopes().iter().position(|s| s == scope)
     }
+
+    pub fn is_16_color(&self) -> bool {
+        self.styles.iter().all(|(_, style)| {
+            [style.fg, style.bg]
+                .into_iter()
+                .all(|color| !matches!(color, Some(Color::Rgb(..))))
+        })
+    }
 }
 
 struct ThemePalette {