From db6fd56aca991b6cfddebc1d8bb952269af72a96 Mon Sep 17 00:00:00 2001
From: Humza Shahid <humzasaur@gmail.com>
Date: Sat, 13 Sep 2025 03:32:35 +0100
Subject: [PATCH] perform bounds checking when we try to index into a vector,
 in LineGap's 'getLineNumberOfIdx' helper functions

---
 src/line_gap.sml | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/line_gap.sml b/src/line_gap.sml
index 8d4cbaa..caa9963 100644
--- a/src/line_gap.sml
+++ b/src/line_gap.sml
@@ -2662,12 +2662,12 @@ struct
               curLine
             else
               let
+                val prevLine = curLine - Vector.length lhd
                 val relativeIdx = findIdx - prevIdx
                 val relativeLine = binSearch (relativeIdx, lhd)
-                val lineOffset = Vector.sub (lhd, relativeLine)
-                val prevLine = curLine - Vector.length lhd
               in
-                prevLine + lineOffset
+                if relativeLine < 0 then prevLine
+                else Vector.sub (lhd, relativeLine) + prevLine
               end
           else
             let val prevLine = curLine - Vector.length lhd
@@ -2691,7 +2691,8 @@ struct
               let
                 val relativeIdx = findIdx - curIdx
                 val relativeLine = binSearch (relativeIdx, lhd)
-                val lineOffset = Vector.sub (lhd, relativeLine)
+                val lineOffset =
+                  if relativeLine < 0 then 0 else Vector.sub (lhd, relativeLine)
               in
                 curLine + lineOffset
               end