Indent guides (#11503)

Builds on top of existing work from #2249, but here's a showcase:


https://github.com/zed-industries/zed/assets/53836821/4b346965-6654-496c-b379-75425d9b493f

TODO:
- [x] handle line wrapping
- [x] implement handling in multibuffer (crashes currently)
- [x] add configuration option
- [x] new theme properties? What colors to use?
- [x] Possibly support indents with different colors or background
colors
- [x] investigate edge cases (e.g. indent guides and folds continue on
empty lines even if the next indent is different)
- [x] add more tests (also test `find_active_indent_index`)
- [x] docs (will do in a follow up PR)
- [x] benchmark performance impact

Release Notes:

- Added indent guides
([#5373](https://github.com/zed-industries/zed/issues/5373))

---------

Co-authored-by: Nate Butler <1714999+iamnbutler@users.noreply.github.com>
Co-authored-by: Remco <djsmits12@gmail.com>

crates/theme/src/styles/accents.rs

@@ -0,0 +1,85 @@
+use gpui::Hsla;
+use serde_derive::Deserialize;
+
+use crate::{
+    amber, blue, cyan, gold, grass, indigo, iris, jade, lime, orange, pink, purple, tomato,
+    try_parse_color, AccentContent,
+};
+
+/// A collection of colors that are used to color indent aware lines in the editor.
+#[derive(Clone, Deserialize)]
+pub struct AccentColors(pub Vec<Hsla>);
+
+impl Default for AccentColors {
+    /// Don't use this!
+    /// We have to have a default to be `[refineable::Refinable]`.
+    /// TODO "Find a way to not need this for Refinable"
+    fn default() -> Self {
+        Self::dark()
+    }
+}
+
+impl AccentColors {
+    pub fn dark() -> Self {
+        Self(vec![
+            blue().dark().step_9(),
+            orange().dark().step_9(),
+            pink().dark().step_9(),
+            lime().dark().step_9(),
+            purple().dark().step_9(),
+            amber().dark().step_9(),
+            jade().dark().step_9(),
+            tomato().dark().step_9(),
+            cyan().dark().step_9(),
+            gold().dark().step_9(),
+            grass().dark().step_9(),
+            indigo().dark().step_9(),
+            iris().dark().step_9(),
+        ])
+    }
+
+    pub fn light() -> Self {
+        Self(vec![
+            blue().light().step_9(),
+            orange().light().step_9(),
+            pink().light().step_9(),
+            lime().light().step_9(),
+            purple().light().step_9(),
+            amber().light().step_9(),
+            jade().light().step_9(),
+            tomato().light().step_9(),
+            cyan().light().step_9(),
+            gold().light().step_9(),
+            grass().light().step_9(),
+            indigo().light().step_9(),
+            iris().light().step_9(),
+        ])
+    }
+}
+
+impl AccentColors {
+    pub fn color_for_index(&self, index: u32) -> Hsla {
+        self.0[index as usize % self.0.len()]
+    }
+
+    /// Merges the given accent colors into this [`AccentColors`] instance.
+    pub fn merge(&mut self, accent_colors: &[AccentContent]) {
+        if accent_colors.is_empty() {
+            return;
+        }
+
+        let colors = accent_colors
+            .iter()
+            .filter_map(|accent_color| {
+                accent_color
+                    .0
+                    .as_ref()
+                    .and_then(|color| try_parse_color(color).ok())
+            })
+            .collect::<Vec<_>>();
+
+        if !colors.is_empty() {
+            self.0 = colors;
+        }
+    }
+}

crates/theme/src/styles/colors.rs

@@ -2,7 +2,9 @@ use gpui::{Hsla, WindowBackgroundAppearance};
 use refineable::Refineable;
 use std::sync::Arc;
 
-use crate::{PlayerColors, StatusColors, StatusColorsRefinement, SyntaxTheme, SystemColors};
+use crate::{
+    AccentColors, PlayerColors, StatusColors, StatusColorsRefinement, SyntaxTheme, SystemColors,
+};
 
 #[derive(Refineable, Clone, Debug)]
 #[refineable(Debug, serde::Deserialize)]
@@ -154,6 +156,8 @@ pub struct ThemeColors {
     pub editor_invisible: Hsla,
     pub editor_wrap_guide: Hsla,
     pub editor_active_wrap_guide: Hsla,
+    pub editor_indent_guide: Hsla,
+    pub editor_indent_guide_active: Hsla,
     /// Read-access of a symbol, like reading a variable.
     ///
     /// A document highlight is a range inside a text document which deserves
@@ -242,7 +246,7 @@ pub struct ThemeStyles {
     /// An array of colors used for theme elements that iterate through a series of colors.
     ///
     /// Example: Player colors, rainbow brackets and indent guides, etc.
-    pub accents: Vec<Hsla>,
+    pub accents: AccentColors,
 
     #[refineable]
     pub colors: ThemeColors,
@@ -251,6 +255,7 @@ pub struct ThemeStyles {
     pub status: StatusColors,
 
     pub player: PlayerColors,
+
     pub syntax: Arc<SyntaxTheme>,
 }