language_settings: Add whitespace_map setting (#37704)

This setting controls which visible characters are used to render
whitespace when the show_whitespace setting is enabled.

Release Notes:

- Added `whitespace_map` setting to control which visible characters are
used to render whitespace when the `show_whitespace` setting is enabled.

---------

Co-authored-by: Nia Espera <nia@zed.dev>

assets/settings/default.json

@@ -362,6 +362,11 @@
   // - It is adjacent to an edge (start or end)
   // - It is adjacent to a whitespace (left or right)
   "show_whitespaces": "selection",
+  // Visible characters used to render whitespace when show_whitespaces is enabled.
+  "whitespace_map": {
+    "space": "•",
+    "tab": "→"
+  },
   // Settings related to calls in Zed
   "calls": {
     // Join calls with the microphone live by default

crates/editor/src/element.rs

@@ -9259,11 +9259,21 @@ impl Element for EditorElement {
                     });
 
                     let invisible_symbol_font_size = font_size / 2.;
+                    let whitespace_map = &self
+                        .editor
+                        .read(cx)
+                        .buffer
+                        .read(cx)
+                        .language_settings(cx)
+                        .whitespace_map;
+
+                    let tab_char = whitespace_map.tab();
+                    let tab_len = tab_char.len();
                     let tab_invisible = window.text_system().shape_line(
-                        "→".into(),
+                        tab_char,
                         invisible_symbol_font_size,
                         &[TextRun {
-                            len: "→".len(),
+                            len: tab_len,
                             font: self.style.text.font(),
                             color: cx.theme().colors().editor_invisible,
                             background_color: None,
@@ -9272,11 +9282,14 @@ impl Element for EditorElement {
                         }],
                         None,
                     );
+
+                    let space_char = whitespace_map.space();
+                    let space_len = space_char.len();
                     let space_invisible = window.text_system().shape_line(
-                        "•".into(),
+                        space_char,
                         invisible_symbol_font_size,
                         &[TextRun {
-                            len: "•".len(),
+                            len: space_len,
                             font: self.style.text.font(),
                             color: cx.theme().colors().editor_invisible,
                             background_color: None,

crates/language/src/language_settings.rs

@@ -8,7 +8,7 @@ use ec4rs::{
     property::{FinalNewline, IndentSize, IndentStyle, MaxLineLen, TabWidth, TrimTrailingWs},
 };
 use globset::{Glob, GlobMatcher, GlobSet, GlobSetBuilder};
-use gpui::{App, Modifiers};
+use gpui::{App, Modifiers, SharedString};
 use itertools::{Either, Itertools};
 use schemars::{JsonSchema, json_schema};
 use serde::{
@@ -123,6 +123,8 @@ pub struct LanguageSettings {
     pub edit_predictions_disabled_in: Vec<String>,
     /// Whether to show tabs and spaces in the editor.
     pub show_whitespaces: ShowWhitespaceSetting,
+    /// Visible characters used to render whitespace when show_whitespaces is enabled.
+    pub whitespace_map: WhitespaceMap,
     /// Whether to start a new line with a comment when a previous line is a comment as well.
     pub extend_comment_on_newline: bool,
     /// Inlay hint related settings.
@@ -578,6 +580,11 @@ pub struct LanguageSettingsContent {
     /// Whether to show tabs and spaces in the editor.
     #[serde(default)]
     pub show_whitespaces: Option<ShowWhitespaceSetting>,
+    /// Visible characters used to render whitespace when show_whitespaces is enabled.
+    ///
+    /// Default: "•" for spaces, "→" for tabs.
+    #[serde(default)]
+    pub whitespace_map: Option<WhitespaceMap>,
     /// Whether to start a new line with a comment when a previous line is a comment as well.
     ///
     /// Default: true
@@ -855,6 +862,28 @@ pub enum ShowWhitespaceSetting {
     Trailing,
 }
 
+#[derive(Clone, Debug, Default, Serialize, Deserialize, JsonSchema, PartialEq, SettingsUi)]
+pub struct WhitespaceMap {
+    #[serde(default)]
+    pub space: Option<String>,
+    #[serde(default)]
+    pub tab: Option<String>,
+}
+
+impl WhitespaceMap {
+    pub fn space(&self) -> SharedString {
+        self.space
+            .as_ref()
+            .map_or_else(|| SharedString::from("•"), |s| SharedString::from(s))
+    }
+
+    pub fn tab(&self) -> SharedString {
+        self.tab
+            .as_ref()
+            .map_or_else(|| SharedString::from("→"), |s| SharedString::from(s))
+    }
+}
+
 /// Controls which formatter should be used when formatting code.
 #[derive(Clone, Debug, Default, PartialEq, Eq, SettingsUi)]
 pub enum SelectedFormatter {
@@ -1643,6 +1672,7 @@ fn merge_settings(settings: &mut LanguageSettings, src: &LanguageSettingsContent
         src.edit_predictions_disabled_in.clone(),
     );
     merge(&mut settings.show_whitespaces, src.show_whitespaces);
+    merge(&mut settings.whitespace_map, src.whitespace_map.clone());
     merge(
         &mut settings.extend_comment_on_newline,
         src.extend_comment_on_newline,