Revert "Fix UTF-8 character boundary panic in DirectWrite text ... (#37767)" (#38800)

Anthony Eid created 1 month ago

This reverts commit 9e7302520ec93a96a9b275a817f083b96620148e.

I run into an infinite hang in Zed nightly and used instruments and
activity monitor to sample what was going on. The root cause seemed to
be the unwrap_unchecked introduced in reverted PR.

Release Notes:

- N/A

Change summary

crates/gpui/src/text_system.rs | 28 +---------------------------
1 file changed, 1 insertion(+), 27 deletions(-)

Detailed changes

crates/gpui/src/text_system.rs

@@ -429,33 +429,7 @@ impl WindowTextSystem {
                     break;
                 };
 
-                let mut run_len_within_line = cmp::min(line_end, run_start + run.len) - run_start;
-
-                // Ensure the run length respects UTF-8 character boundaries
-                if run_len_within_line > 0 {
-                    let text_slice = &line_text[run_start - line_start..];
-                    if run_len_within_line < text_slice.len()
-                        && !text_slice.is_char_boundary(run_len_within_line)
-                    {
-                        // Find the previous character boundary using efficient bit-level checking
-                        // UTF-8 characters are at most 4 bytes, so we only need to check up to 3 bytes back
-                        let lower_bound = run_len_within_line.saturating_sub(3);
-                        let search_range =
-                            &text_slice.as_bytes()[lower_bound..=run_len_within_line];
-
-                        // SAFETY: A valid character boundary must exist in this range because:
-                        // 1. run_len_within_line is a valid position in the string slice
-                        // 2. UTF-8 characters are at most 4 bytes, so some boundary exists in [run_len_within_line-3..=run_len_within_line]
-                        let pos_from_lower = unsafe {
-                            search_range
-                                .iter()
-                                .rposition(|&b| (b as i8) >= -0x40)
-                                .unwrap_unchecked()
-                        };
-
-                        run_len_within_line = lower_bound + pos_from_lower;
-                    }
-                }
+                let run_len_within_line = cmp::min(line_end, run_start + run.len) - run_start;
 
                 if last_font == Some(run.font.clone()) {
                     font_runs.last_mut().unwrap().len += run_len_within_line;