Load alt default theme if true color is not supported

* Move `runtime/themes/base16_default_terminal.toml` to
  `base16_theme.toml` alongside `theme.toml`
* Use `terminfo` crate to detect whether the terminal supports true
  color and, if the user has no theme configured and their terminal does
  not support true color, load the alt default theme instead of the
  normal default.

Remove `terminfo` dependency, use `COLORTERM` env instead

Prevent user from switching to an unsupported theme

Add `true-color-override` option

If the terminal is wrongly detected to not support true color,
`true-color-override = true` will override the detection.

Rename `true-color-override` to `true-color`

1 files changed, 20 insertions, 0 deletions

diff --git a/helix-view/src/theme.rs b/helix-view/src/theme.rs
index 47fc6262..ddcdad99 100644
--- a/helix-view/src/theme.rs
+++ b/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_theme.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)]
@@ -154,6 +166,14 @@ 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 {