Respect max line limit for invisible character replacements (#57137)

This change makes sure that `LineWithInvisibles::from_chunks` applies
the max line length limit to invisible character replacements as it does
to normal text chunks.

Without this change, pathological lines containing many invisible
characters could produce unbounded number of line fragments.

Closes FR-6.

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable


Release Notes:

- Fixed a rare panic that could occur when lines in the editor contained
many invisible characters.

crates/editor/src/element.rs

@@ -9001,6 +9001,15 @@ impl LineWithInvisibles {
             replacement: None,
         }]) {
             if let Some(replacement) = highlighted_chunk.replacement {
+                if line_exceeded_max_len {
+                    continue;
+                }
+
+                if len + line.len() + highlighted_chunk.text.len() > max_line_len {
+                    line_exceeded_max_len = true;
+                    continue;
+                }
+
                 if !line.is_empty() {
                     let segments = bg_segments_per_row.get(row).map(|v| &v[..]).unwrap_or(&[]);
                     let text_runs: &[TextRun] = if segments.is_empty() {
@@ -9132,8 +9141,9 @@ impl LineWithInvisibles {
                             Cow::Borrowed(text_style)
                         };
 
-                        if line.len() + line_chunk.len() > max_line_len {
-                            let mut chunk_len = max_line_len - line.len();
+                        let current_line_len = len + line.len();
+                        if current_line_len + line_chunk.len() > max_line_len {
+                            let mut chunk_len = max_line_len - current_line_len;
                             while !line_chunk.is_char_boundary(chunk_len) {
                                 chunk_len -= 1;
                             }
@@ -9141,6 +9151,10 @@ impl LineWithInvisibles {
                             line_exceeded_max_len = true;
                         }
 
+                        if line_chunk.is_empty() {
+                            continue;
+                        }
+
                         styles.push(TextRun {
                             len: line_chunk.len(),
                             font: text_style.font(),
@@ -13573,6 +13587,67 @@ mod tests {
         );
     }
 
+    #[gpui::test]
+    fn test_replacement_chunks_are_clipped_to_max_line_len(cx: &mut TestAppContext) {
+        init_test(cx, |_| {});
+
+        let window = cx.add_window(|window, cx| {
+            let buffer = MultiBuffer::build_simple("", cx);
+            Editor::new(EditorMode::full(), buffer, None, window, cx)
+        });
+        let cx = &mut VisualTestContext::from_window(*window, cx);
+        let editor = window.root(cx).unwrap();
+        let style = cx.update(|_, cx| editor.update(cx, |editor, cx| editor.style(cx).clone()));
+        let editor_mode = EditorMode::full();
+        let max_line_len = "\u{00a0}abcdef".len();
+
+        window
+            .update(cx, |_, window, cx| {
+                let chunks = std::iter::once(HighlightedChunk {
+                    text: "\u{00a0}",
+                    style: None,
+                    is_tab: false,
+                    is_inlay: false,
+                    replacement: Some(ChunkReplacement::Str("\u{2007}".into())),
+                })
+                .chain(std::iter::once(HighlightedChunk {
+                    text: "abcdefghi",
+                    style: None,
+                    is_tab: false,
+                    is_inlay: false,
+                    replacement: None,
+                }))
+                .chain(
+                    std::iter::repeat_with(|| HighlightedChunk {
+                        text: "\u{00a0}",
+                        style: None,
+                        is_tab: false,
+                        is_inlay: false,
+                        replacement: Some(ChunkReplacement::Str("\u{2007}".into())),
+                    })
+                    .take(8),
+                );
+
+                let layouts = LineWithInvisibles::from_chunks(
+                    chunks,
+                    &style,
+                    max_line_len,
+                    1,
+                    &editor_mode,
+                    px(500.),
+                    |_| false,
+                    &[],
+                    window,
+                    cx,
+                );
+
+                assert_eq!(layouts.len(), 1);
+                assert_eq!(layouts[0].len, max_line_len);
+                assert!(layouts[0].fragments.len() <= max_line_len);
+            })
+            .unwrap();
+    }
+
     #[gpui::test]
     fn test_invisibles_dont_appear_in_certain_editors(cx: &mut TestAppContext) {
         init_test(cx, |s| {