editor: Add debounce setting for triggering DocumentHighlight (#21702)

Closes https://github.com/zed-industries/zed/issues/6843


I don't see where is the logic to remove old document highlight when new
one applies,
ideally, old highlight should be cleared as soon as possible when cursor
moves if the new position does not
sits in old highlight ranges to avoid linger highlights described in
https://github.com/zed-industries/zed/issues/13682#issuecomment-2498368680.

So current solution is still not ideal, because only when lsp responses
highlight ranges (even is a empty set) can we clear the old one.

Release Notes:

- Added a setting `lsp_highlight_debounce` to configure delay for
querying highlights from language server.

---------

Co-authored-by: mgsloan@gmail.com <michael@zed.dev>

assets/settings/default.json

@@ -144,6 +144,9 @@
   // 4. Highlight the full line (default):
   //    "all"
   "current_line_highlight": "all",
+  // The debounce delay before querying highlights from the language
+  // server based on the current cursor location.
+  "lsp_highlight_debounce": 75,
   // Whether to pop the completions menu while typing in an editor without
   // explicitly requesting it.
   "show_completions_on_input": true,

crates/editor/src/editor.rs

@@ -190,8 +190,6 @@ const MAX_SELECTION_HISTORY_LEN: usize = 1024;
 pub(crate) const CURSORS_VISIBLE_FOR: Duration = Duration::from_millis(2000);
 #[doc(hidden)]
 pub const CODE_ACTIONS_DEBOUNCE_TIMEOUT: Duration = Duration::from_millis(250);
-#[doc(hidden)]
-pub const DOCUMENT_HIGHLIGHTS_DEBOUNCE_TIMEOUT: Duration = Duration::from_millis(75);
 
 pub(crate) const FORMAT_TIMEOUT: Duration = Duration::from_secs(2);
 pub(crate) const SCROLL_CENTER_TOP_BOTTOM_DEBOUNCE_TIMEOUT: Duration = Duration::from_secs(1);
@@ -4311,10 +4309,10 @@ impl Editor {
         if cursor_buffer != tail_buffer {
             return None;
         }
-
+        let debounce = EditorSettings::get_global(cx).lsp_highlight_debounce;
         self.document_highlights_task = Some(cx.spawn(|this, mut cx| async move {
             cx.background_executor()
-                .timer(DOCUMENT_HIGHLIGHTS_DEBOUNCE_TIMEOUT)
+                .timer(Duration::from_millis(debounce))
                 .await;
 
             let highlights = if let Some(highlights) = cx

crates/editor/src/editor_settings.rs

@@ -9,6 +9,7 @@ pub struct EditorSettings {
     pub cursor_blink: bool,
     pub cursor_shape: Option<CursorShape>,
     pub current_line_highlight: CurrentLineHighlight,
+    pub lsp_highlight_debounce: u64,
     pub hover_popover_enabled: bool,
     pub toolbar: Toolbar,
     pub scrollbar: Scrollbar,
@@ -185,6 +186,11 @@ pub struct EditorSettingsContent {
     ///
     /// Default: all
     pub current_line_highlight: Option<CurrentLineHighlight>,
+    /// The debounce delay before querying highlights from the language
+    /// server based on the current cursor location.
+    ///
+    /// Default: 75
+    pub lsp_highlight_debounce: Option<u64>,
     /// Whether to show the informational hover box when moving the mouse
     /// over symbols in the editor.
     ///

docs/src/configuring-zed.md

@@ -467,6 +467,12 @@ List of `string` values
 "current_line_highlight": "all"
 ```
 
+## LSP Highlight Debounce
+
+- Description: The debounce delay before querying highlights from the language server based on the current cursor location.
+- Setting: `lsp_highlight_debounce`
+- Default: `75`
+
 ## Cursor Blink
 
 - Description: Whether or not the cursor blinks.