editor: Add language setting for comment continuations (#2605)

Per @JosephTLyons request I've added a language setting for comment
continuations.

Release Notes:

- Added a language setting for comment continuations.

assets/settings/default.json

@@ -108,6 +108,8 @@
   // Whether or not to remove any trailing whitespace from lines of a buffer
   // before saving it.
   "remove_trailing_whitespace_on_save": true,
+  // Whether to start a new line with a comment when a previous line is a comment as well.
+  "extend_comment_on_newline": true,
   // Whether or not to ensure there's a single newline at the end of a buffer
   // when saving it.
   "ensure_final_newline_on_save": true,

crates/editor/src/editor.rs

@@ -2169,8 +2169,8 @@ impl Editor {
         self.transact(cx, |this, cx| {
             let (edits, selection_fixup_info): (Vec<_>, Vec<_>) = {
                 let selections = this.selections.all::<usize>(cx);
-
-                let buffer = this.buffer.read(cx).snapshot(cx);
+                let multi_buffer = this.buffer.read(cx);
+                let buffer = multi_buffer.snapshot(cx);
                 selections
                     .iter()
                     .map(|selection| {
@@ -2181,8 +2181,9 @@ impl Editor {
                         let end = selection.end;
                         let is_cursor = start == end;
                         let language_scope = buffer.language_scope_at(start);
-                        let (comment_delimiter, insert_extra_newline) =
-                            if let Some(language) = &language_scope {
+                        let (comment_delimiter, insert_extra_newline) = if let Some(language) =
+                            &language_scope
+                        {
                             let leading_whitespace_len = buffer
                                 .reversed_chars_at(start)
                                 .take_while(|c| c.is_whitespace() && *c != '\n')
@@ -2213,8 +2214,11 @@ impl Editor {
                                         )
                                 });
                             // Comment extension on newline is allowed only for cursor selections
-                                let comment_delimiter =
-                                    language.line_comment_prefix().filter(|_| is_cursor);
+                            let comment_delimiter = language.line_comment_prefix().filter(|_| {
+                                let is_comment_extension_enabled =
+                                    multi_buffer.settings_at(0, cx).extend_comment_on_newline;
+                                is_cursor && is_comment_extension_enabled
+                            });
                             let comment_delimiter = if let Some(delimiter) = comment_delimiter {
                                 buffer
                                     .buffer_line_for_row(start_point.row)

crates/editor/src/editor_tests.rs

@@ -1732,7 +1732,7 @@ async fn test_newline_comments(cx: &mut gpui::TestAppContext) {
         },
         None,
     ));
-
+    {
         let mut cx = EditorTestContext::new(cx).await;
         cx.update_buffer(|buffer, cx| buffer.set_language(Some(language), cx));
         cx.set_state(indoc! {"
@@ -1753,6 +1753,20 @@ async fn test_newline_comments(cx: &mut gpui::TestAppContext) {
 
         ˇ// Foo
     "});
+    }
+    // Ensure that comment continuations can be disabled.
+    update_test_settings(cx, |settings| {
+        settings.defaults.extend_comment_on_newline = Some(false);
+    });
+    let mut cx = EditorTestContext::new(cx).await;
+    cx.set_state(indoc! {"
+        // Fooˇ
+    "});
+    cx.update_editor(|e, cx| e.newline(&Newline, cx));
+    cx.assert_editor_state(indoc! {"
+        // Foo
+        ˇ
+    "});
 }
 
 #[gpui::test]

crates/language/src/language_settings.rs

@@ -51,6 +51,7 @@ pub struct LanguageSettings {
     pub enable_language_server: bool,
     pub show_copilot_suggestions: bool,
     pub show_whitespaces: ShowWhitespaceSetting,
+    pub extend_comment_on_newline: bool,
 }
 
 #[derive(Clone, Debug, Default)]
@@ -95,6 +96,8 @@ pub struct LanguageSettingsContent {
     pub show_copilot_suggestions: Option<bool>,
     #[serde(default)]
     pub show_whitespaces: Option<ShowWhitespaceSetting>,
+    #[serde(default)]
+    pub extend_comment_on_newline: Option<bool>,
 }
 
 #[derive(Clone, Debug, Default, Serialize, Deserialize, JsonSchema)]
@@ -340,7 +343,10 @@ fn merge_settings(settings: &mut LanguageSettings, src: &LanguageSettingsContent
         src.show_copilot_suggestions,
     );
     merge(&mut settings.show_whitespaces, src.show_whitespaces);
-
+    merge(
+        &mut settings.extend_comment_on_newline,
+        src.extend_comment_on_newline,
+    );
     fn merge<T>(target: &mut T, value: Option<T>) {
         if let Some(value) = value {
             *target = value;