From d92d52b508c11092ca51a1174be14aabcc2fe5f2 Mon Sep 17 00:00:00 2001
From: Michael Sloan <michael@zed.dev>
Date: Tue, 17 Jun 2025 01:26:58 -0600
Subject: [PATCH] Attempt to log error instead of crash in bracket highlighting
 (#32837)

Crashes look like:

```
Panic `offset 632 is greater than the snapshot.len() 631` on thread 0 (com.apple.main-thread)

<multi_buffer::MultiBufferSnapshot>::innermost_enclosing_bracket_ranges::<usize>
editor::highlight_matching_bracket::refresh_matching_bracket_highlights
<gpui::app::App>::update_window_id::<bool, <gpui::app::context::Context<editor::Editor>>::subscribe_in<multi_buffer::MultiBuffer, multi_buffer::Event, <editor::Editor>::on_buffer_event>::{closure#0}::{closure#0}>::{closure#0}
<gpui::app::context::Context<editor::Editor>>::subscribe_in::<multi_buffer::MultiBuffer, multi_buffer::Event, <editor::Editor>::on_buffer_event>::{closure#0}
<gpui::app::App>::flush_effects
<project::lsp_store::LocalLspStore>::format_buffer_locally::{closure#0}
<project::lsp_store::LspStore>::format::{closure#1}::{closure#0}::<i32>
```

Though `format_buffer_locally` is not always present. Both issue reports
mention usage of the agent. I suspect this is somehow a result of agent
format-on-save combined with the user's cursor being at the end of the
buffer as it's getting edited by the agent.

The offsets are always off-by-one in the error, so at first I thought
the issue was the condition `head < snapshot.buffer_snapshot.len()`
before setting `tail` to be `head + 1`, but an offset equal to len is
valid. Seems like to get a `to_offset` crash, `head` must be greater
than `len`. Which is quite weird, a selection's offset should never be
out of bounds.

Since this code is just about highlighting brackets, this PR logs an
error instead of crashing in the `head > len` case.

Closes #32732, #32171

Release Notes:

- N/A
---
 crates/editor/src/highlight_matching_bracket.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/crates/editor/src/highlight_matching_bracket.rs b/crates/editor/src/highlight_matching_bracket.rs
index 778f5783e2..e38197283d 100644
--- a/crates/editor/src/highlight_matching_bracket.rs
+++ b/crates/editor/src/highlight_matching_bracket.rs
@@ -19,6 +19,11 @@ pub fn refresh_matching_bracket_highlights(
 
     let snapshot = editor.snapshot(window, cx);
     let head = newest_selection.head();
+    if head > snapshot.buffer_snapshot.len() {
+        log::error!("bug: cursor offset is out of range while refreshing bracket highlights");
+        return;
+    }
+
     let mut tail = head;
     if (editor.cursor_shape == CursorShape::Block || editor.cursor_shape == CursorShape::Hollow)
         && head < snapshot.buffer_snapshot.len()