Remove auto-width editor type (#34438)

Closes #34044

`EditorMode::SingleLine { auto_width: true }` was only used for the
title editor in the rules library, and following
https://github.com/zed-industries/zed/pull/31994 we can replace that
with a normal single-line editor without problems. The auto-width editor
was interacting badly with the recently-added newline visualization
code, causing a panic during layout---by switching it to
`Editor::single_line` the newline visualization works there too.

Release Notes:

- Fixed a panic that could occur when opening the rules library.

---------

Co-authored-by: Finn <finn@zed.dev>

crates/editor/src/editor.rs

@@ -482,9 +482,7 @@ pub enum SelectMode {
 
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub enum EditorMode {
-    SingleLine {
-        auto_width: bool,
-    },
+    SingleLine,
     AutoHeight {
         min_lines: usize,
         max_lines: Option<usize>,
@@ -1662,13 +1660,7 @@ impl Editor {
     pub fn single_line(window: &mut Window, cx: &mut Context<Self>) -> Self {
         let buffer = cx.new(|cx| Buffer::local("", cx));
         let buffer = cx.new(|cx| MultiBuffer::singleton(buffer, cx));
-        Self::new(
-            EditorMode::SingleLine { auto_width: false },
-            buffer,
-            None,
-            window,
-            cx,
-        )
+        Self::new(EditorMode::SingleLine, buffer, None, window, cx)
     }
 
     pub fn multi_line(window: &mut Window, cx: &mut Context<Self>) -> Self {
@@ -1677,18 +1669,6 @@ impl Editor {
         Self::new(EditorMode::full(), buffer, None, window, cx)
     }
 
-    pub fn auto_width(window: &mut Window, cx: &mut Context<Self>) -> Self {
-        let buffer = cx.new(|cx| Buffer::local("", cx));
-        let buffer = cx.new(|cx| MultiBuffer::singleton(buffer, cx));
-        Self::new(
-            EditorMode::SingleLine { auto_width: true },
-            buffer,
-            None,
-            window,
-            cx,
-        )
-    }
-
     pub fn auto_height(
         min_lines: usize,
         max_lines: usize,

crates/editor/src/element.rs

@@ -7777,46 +7777,13 @@ impl Element for EditorElement {
                 editor.set_style(self.style.clone(), window, cx);
 
                 let layout_id = match editor.mode {
-                    EditorMode::SingleLine { auto_width } => {
+                    EditorMode::SingleLine => {
                         let rem_size = window.rem_size();
-
                         let height = self.style.text.line_height_in_pixels(rem_size);
-                        if auto_width {
-                            let editor_handle = cx.entity().clone();
-                            let style = self.style.clone();
-                            window.request_measured_layout(
-                                Style::default(),
-                                move |_, _, window, cx| {
-                                    let editor_snapshot = editor_handle
-                                        .update(cx, |editor, cx| editor.snapshot(window, cx));
-                                    let line = Self::layout_lines(
-                                        DisplayRow(0)..DisplayRow(1),
-                                        &editor_snapshot,
-                                        &style,
-                                        px(f32::MAX),
-                                        |_| false, // Single lines never soft wrap
-                                        window,
-                                        cx,
-                                    )
-                                    .pop()
-                                    .unwrap();
-
-                                    let font_id =
-                                        window.text_system().resolve_font(&style.text.font());
-                                    let font_size =
-                                        style.text.font_size.to_pixels(window.rem_size());
-                                    let em_width =
-                                        window.text_system().em_width(font_id, font_size).unwrap();
-
-                                    size(line.width + em_width, height)
-                                },
-                            )
-                        } else {
-                            let mut style = Style::default();
-                            style.size.height = height.into();
-                            style.size.width = relative(1.).into();
-                            window.request_layout(style, None, cx)
-                        }
+                        let mut style = Style::default();
+                        style.size.height = height.into();
+                        style.size.width = relative(1.).into();
+                        window.request_layout(style, None, cx)
                     }
                     EditorMode::AutoHeight {
                         min_lines,
@@ -10388,7 +10355,7 @@ mod tests {
         });
 
         for editor_mode_without_invisibles in [
-            EditorMode::SingleLine { auto_width: false },
+            EditorMode::SingleLine,
             EditorMode::AutoHeight {
                 min_lines: 1,
                 max_lines: Some(100),

crates/rules_library/src/rules_library.rs

@@ -611,7 +611,7 @@ impl RulesLibrary {
                 this.update_in(cx, |this, window, cx| match rule {
                     Ok(rule) => {
                         let title_editor = cx.new(|cx| {
-                            let mut editor = Editor::auto_width(window, cx);
+                            let mut editor = Editor::single_line(window, cx);
                             editor.set_placeholder_text("Untitled", cx);
                             editor.set_text(rule_metadata.title.unwrap_or_default(), window, cx);
                             if prompt_id.is_built_in() {