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/editor/src/editor.rs

@@ -26,6 +26,7 @@ mod git;
 mod highlight_matching_bracket;
 mod hover_links;
 mod hover_popover;
+mod indent_guides;
 mod inline_completion_provider;
 pub mod items;
 mod mouse_context_menu;
@@ -76,6 +77,7 @@ use highlight_matching_bracket::refresh_matching_bracket_highlights;
 use hover_popover::{hide_hover, HoverState};
 use hunk_diff::ExpandedHunks;
 pub(crate) use hunk_diff::HunkToExpand;
+use indent_guides::ActiveIndentGuidesState;
 use inlay_hint_cache::{InlayHintCache, InlaySplice, InvalidationStrategy};
 pub use inline_completion_provider::*;
 pub use items::MAX_TAB_TITLE_LEN;
@@ -453,11 +455,13 @@ pub struct Editor {
     show_git_diff_gutter: Option<bool>,
     show_code_actions: Option<bool>,
     show_wrap_guides: Option<bool>,
+    show_indent_guides: Option<bool>,
     placeholder_text: Option<Arc<str>>,
     highlight_order: usize,
     highlighted_rows: HashMap<TypeId, Vec<RowHighlight>>,
     background_highlights: TreeMap<TypeId, BackgroundHighlight>,
     scrollbar_marker_state: ScrollbarMarkerState,
+    active_indent_guides_state: ActiveIndentGuidesState,
     nav_history: Option<ItemNavHistory>,
     context_menu: RwLock<Option<ContextMenu>>,
     mouse_context_menu: Option<MouseContextMenu>,
@@ -1656,11 +1660,13 @@ impl Editor {
             show_git_diff_gutter: None,
             show_code_actions: None,
             show_wrap_guides: None,
+            show_indent_guides: None,
             placeholder_text: None,
             highlight_order: 0,
             highlighted_rows: HashMap::default(),
             background_highlights: Default::default(),
             scrollbar_marker_state: ScrollbarMarkerState::default(),
+            active_indent_guides_state: ActiveIndentGuidesState::default(),
             nav_history: None,
             context_menu: RwLock::new(None),
             mouse_context_menu: None,
@@ -9440,6 +9446,7 @@ impl Editor {
 
             cx.notify();
             self.scrollbar_marker_state.dirty = true;
+            self.active_indent_guides_state.dirty = true;
         }
     }
 
@@ -9668,6 +9675,11 @@ impl Editor {
         cx.notify();
     }
 
+    pub fn set_show_indent_guides(&mut self, show_indent_guides: bool, cx: &mut ViewContext<Self>) {
+        self.show_indent_guides = Some(show_indent_guides);
+        cx.notify();
+    }
+
     pub fn reveal_in_finder(&mut self, _: &RevealInFinder, cx: &mut ViewContext<Self>) {
         if let Some(buffer) = self.buffer().read(cx).as_singleton() {
             if let Some(file) = buffer.read(cx).file().and_then(|f| f.as_local()) {
@@ -10303,6 +10315,7 @@ impl Editor {
                 singleton_buffer_edited,
             } => {
                 self.scrollbar_marker_state.dirty = true;
+                self.active_indent_guides_state.dirty = true;
                 self.refresh_active_diagnostics(cx);
                 self.refresh_code_actions(cx);
                 if self.has_active_inline_completion(cx) {