From ec0eeaf69df7efbea07e64ceb82e7e4e9b751d4c Mon Sep 17 00:00:00 2001
From: Lukas Wirth <lukas@zed.dev>
Date: Wed, 15 Oct 2025 15:28:51 +0200
Subject: [PATCH] rope: Assert utf8 boundary of start of `Chunks::new` range
 (#40253)

We seem to run into panics in related code, so better assert early

Release Notes:

- N/A *or* Added/Fixed/Improved ...
---
 crates/rope/src/rope.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/crates/rope/src/rope.rs b/crates/rope/src/rope.rs
index c349f3f451..db79e6b03f 100644
--- a/crates/rope/src/rope.rs
+++ b/crates/rope/src/rope.rs
@@ -673,6 +673,12 @@ impl<'a> Chunks<'a> {
             chunks.seek(&range.start, Bias::Right);
             range.start
         };
+        let chunk_offset = offset - chunks.start();
+        if let Some(chunk) = chunks.item()
+            && !chunk.text.is_char_boundary(chunk_offset)
+        {
+            panic!("byte index {} is not a char boundary", offset);
+        }
         Self {
             chunks,
             range,