Fix soft_wrap setting not applying to buffers starting with a different language (#25880)

Closes #22999 
# Problem

Currently, the default soft wrap mode of an editor is determined by
reading the language-specific settings of the language _at offset zero_
in the editor's (multi)buffer. While this provides a way to pick a
single soft wrap mode for a multi-language multibuffer, it's a bad
choice for a single-buffer multibuffer that begins with a different
embedded language. For example, Markdown with frontmatter:

```markdown
---
my_front_matter
---

# Hello World
```

Setting this in config:

```json
  "languages": {
    "Markdown": { "soft_wrap": "bounded" }
  },
```

Will not soft wrap the Markdown file as the language at offset zero is
YAML.

# Solution

Instead of using the language at offset zero, use the language of the
first buffer in the multibuffer (the buffer at offset zero). This gives
better behavior for single-buffer editors, and a similar default for
multi-language multibuffers as before.

# Testing

All existing `editor` crate tests pass, but I would appreciate any
guidance for where best to add additional testing.

Release Notes:

- Fixed soft_wrap setting not applying to buffers starting with a
different language

---------

Co-authored-by: Kirill Bulatov <kirill@zed.dev>

crates/editor/src/editor.rs

@@ -2877,7 +2877,7 @@ impl Editor {
                 }
 
                 if let Some(bracket_pair) = bracket_pair {
-                    let snapshot_settings = snapshot.settings_at(selection.start, cx);
+                    let snapshot_settings = snapshot.language_settings_at(selection.start, cx);
                     let autoclose = self.use_autoclose && snapshot_settings.use_autoclose;
                     let auto_surround =
                         self.use_auto_surround && snapshot_settings.use_auto_surround;
@@ -2942,7 +2942,7 @@ impl Editor {
                         }
 
                         let always_treat_brackets_as_autoclosed = snapshot
-                            .settings_at(selection.start, cx)
+                            .language_settings_at(selection.start, cx)
                             .always_treat_brackets_as_autoclosed;
                         if always_treat_brackets_as_autoclosed
                             && is_bracket_pair_end
@@ -3225,7 +3225,7 @@ impl Editor {
                                     return None;
                                 }
 
-                                if !multi_buffer.settings_at(0, cx).extend_comment_on_newline {
+                                if !multi_buffer.language_settings(cx).extend_comment_on_newline {
                                     return None;
                                 }
 
@@ -3554,7 +3554,7 @@ impl Editor {
                 }
 
                 let always_treat_brackets_as_autoclosed = buffer
-                    .settings_at(selection.start, cx)
+                    .language_settings_at(selection.start, cx)
                     .always_treat_brackets_as_autoclosed;
 
                 if !always_treat_brackets_as_autoclosed {
@@ -7328,7 +7328,7 @@ impl Editor {
             }
 
             // Otherwise, insert a hard or soft tab.
-            let settings = buffer.settings_at(cursor, cx);
+            let settings = buffer.language_settings_at(cursor, cx);
             let tab_size = if settings.hard_tabs {
                 IndentSize::tab()
             } else {
@@ -7392,7 +7392,7 @@ impl Editor {
         delta_for_start_row: u32,
         cx: &App,
     ) -> u32 {
-        let settings = buffer.settings_at(selection.start, cx);
+        let settings = buffer.language_settings_at(selection.start, cx);
         let tab_size = settings.tab_size.get();
         let indent_kind = if settings.hard_tabs {
             IndentKind::Tab
@@ -7472,7 +7472,7 @@ impl Editor {
             let buffer = self.buffer.read(cx);
             let snapshot = buffer.snapshot(cx);
             for selection in &selections {
-                let settings = buffer.settings_at(selection.start, cx);
+                let settings = buffer.language_settings_at(selection.start, cx);
                 let tab_size = settings.tab_size.get();
                 let mut rows = selection.spanned_rows(false, &display_map);
 
@@ -8484,7 +8484,7 @@ impl Editor {
                 continue;
             }
 
-            let tab_size = buffer.settings_at(selection.head(), cx).tab_size;
+            let tab_size = buffer.language_settings_at(selection.head(), cx).tab_size;
 
             // Since not all lines in the selection may be at the same indent
             // level, choose the indent size that is the most common between all
@@ -8530,7 +8530,7 @@ impl Editor {
                 inside_comment = true;
             }
 
-            let language_settings = buffer.settings_at(selection.head(), cx);
+            let language_settings = buffer.language_settings_at(selection.head(), cx);
             let allow_rewrap_based_on_language = match language_settings.allow_rewrap {
                 RewrapBehavior::InComments => inside_comment,
                 RewrapBehavior::InSelections => !selection.is_empty(),
@@ -8586,7 +8586,7 @@ impl Editor {
             };
 
             let wrap_column = buffer
-                .settings_at(Point::new(start_row, 0), cx)
+                .language_settings_at(Point::new(start_row, 0), cx)
                 .preferred_line_length as usize;
             let wrapped_text = wrap_with_prefix(
                 line_prefix,
@@ -8772,8 +8772,9 @@ impl Editor {
 
                 this.buffer.update(cx, |buffer, cx| {
                     let snapshot = buffer.read(cx);
-                    auto_indent_on_paste =
+                    auto_indent_on_paste = snapshot
-                        snapshot.settings_at(cursor_offset, cx).auto_indent_on_paste;
+                        .language_settings_at(cursor_offset, cx)
+                        .auto_indent_on_paste;
 
                     let mut start_offset = 0;
                     let mut edits = Vec::new();
@@ -14082,13 +14083,17 @@ impl Editor {
             return wrap_guides;
         }
 
-        let settings = self.buffer.read(cx).settings_at(0, cx);
+        let settings = self.buffer.read(cx).language_settings(cx);
         if settings.show_wrap_guides {
-            if let SoftWrap::Column(soft_wrap) = self.soft_wrap_mode(cx) {
+            match self.soft_wrap_mode(cx) {
+                SoftWrap::Column(soft_wrap) => {
                     wrap_guides.push((soft_wrap as usize, true));
-            } else if let SoftWrap::Bounded(soft_wrap) = self.soft_wrap_mode(cx) {
+                }
+                SoftWrap::Bounded(soft_wrap) => {
                     wrap_guides.push((soft_wrap as usize, true));
                 }
+                SoftWrap::GitDiff | SoftWrap::None | SoftWrap::EditorWidth => {}
+            }
             wrap_guides.extend(settings.wrap_guides.iter().map(|guide| (*guide, false)))
         }
 
@@ -14096,7 +14101,7 @@ impl Editor {
     }
 
     pub fn soft_wrap_mode(&self, cx: &App) -> SoftWrap {
-        let settings = self.buffer.read(cx).settings_at(0, cx);
+        let settings = self.buffer.read(cx).language_settings(cx);
         let mode = self.soft_wrap_mode_override.unwrap_or(settings.soft_wrap);
         match mode {
             language_settings::SoftWrap::PreferLine | language_settings::SoftWrap::None => {
@@ -14195,7 +14200,7 @@ impl Editor {
         let currently_enabled = self.should_show_indent_guides().unwrap_or_else(|| {
             self.buffer
                 .read(cx)
-                .settings_at(0, cx)
+                .language_settings(cx)
                 .indent_guides
                 .enabled
         });
@@ -15844,7 +15849,7 @@ impl Editor {
         let copilot_enabled_for_language = self
             .buffer
             .read(cx)
-            .settings_at(0, cx)
+            .language_settings(cx)
             .show_edit_predictions;
 
         let project = project.read(cx);

crates/editor/src/element.rs

@@ -4685,7 +4685,7 @@ impl EditorElement {
             .read(cx)
             .buffer
             .read(cx)
-            .settings_at(0, cx)
+            .language_settings(cx)
             .show_whitespaces;
 
         for (ix, line_with_invisibles) in layout.position_map.line_layouts.iter().enumerate() {

crates/multi_buffer/src/multi_buffer.rs

@@ -2307,7 +2307,27 @@ impl MultiBuffer {
             .and_then(|(buffer, offset)| buffer.read(cx).language_at(offset))
     }
 
-    pub fn settings_at<'a, T: ToOffset>(&self, point: T, cx: &'a App) -> Cow<'a, LanguageSettings> {
+    pub fn language_settings<'a>(&'a self, cx: &'a App) -> Cow<'a, LanguageSettings> {
+        let buffer_id = self
+            .snapshot
+            .borrow()
+            .excerpts
+            .first()
+            .map(|excerpt| excerpt.buffer.remote_id());
+        buffer_id
+            .and_then(|buffer_id| self.buffer(buffer_id))
+            .map(|buffer| {
+                let buffer = buffer.read(cx);
+                language_settings(buffer.language().map(|l| l.name()), buffer.file(), cx)
+            })
+            .unwrap_or_else(move || self.language_settings_at(0, cx))
+    }
+
+    pub fn language_settings_at<'a, T: ToOffset>(
+        &'a self,
+        point: T,
+        cx: &'a App,
+    ) -> Cow<'a, LanguageSettings> {
         let mut language = None;
         let mut file = None;
         if let Some((buffer, offset)) = self.point_to_buffer_offset(point, cx) {
@@ -4259,7 +4279,7 @@ impl MultiBufferSnapshot {
     pub fn indent_and_comment_for_line(&self, row: MultiBufferRow, cx: &App) -> String {
         let mut indent = self.indent_size_for_line(row).chars().collect::<String>();
 
-        if self.settings_at(0, cx).extend_comment_on_newline {
+        if self.language_settings(cx).extend_comment_on_newline {
             if let Some(language_scope) = self.language_scope_at(Point::new(row.0, 0)) {
                 let delimiters = language_scope.line_comment_prefixes();
                 for delimiter in delimiters {
@@ -5592,7 +5612,21 @@ impl MultiBufferSnapshot {
             .and_then(|(buffer, offset)| buffer.language_at(offset))
     }
 
-    pub fn settings_at<'a, T: ToOffset>(
+    fn language_settings<'a>(&'a self, cx: &'a App) -> Cow<'a, LanguageSettings> {
+        self.excerpts
+            .first()
+            .map(|excerpt| &excerpt.buffer)
+            .map(|buffer| {
+                language_settings(
+                    buffer.language().map(|language| language.name()),
+                    buffer.file(),
+                    cx,
+                )
+            })
+            .unwrap_or_else(move || self.language_settings_at(0, cx))
+    }
+
+    pub fn language_settings_at<'a, T: ToOffset>(
         &'a self,
         point: T,
         cx: &'a App,

crates/vim/src/normal/paste.rs

@@ -160,7 +160,7 @@ impl Vim {
                     .buffer()
                     .read(cx)
                     .snapshot(cx)
-                    .settings_at(cursor_offset, cx)
+                    .language_settings_at(cursor_offset, cx)
                     .auto_indent_on_paste
                 {
                     editor.edit_with_block_indent(edits, original_start_columns, cx);