From 8b7bbebeeb5b021434c19d24f82e1cc798ebe53f Mon Sep 17 00:00:00 2001
From: Benno Schulenberg <bensberg@justemail.net>
Date: Sun, 19 Mar 2017 18:01:43 +0100
Subject: [PATCH] tweaks: add a warning for a condition that should never occur

---
 src/winio.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/winio.c b/src/winio.c
index 0b2abcbb..0d591497 100644
--- a/src/winio.c
+++ b/src/winio.c
@@ -2667,8 +2667,11 @@ int update_line(filestruct *fileptr, size_t index)
     row = fileptr->lineno - openfile->edittop->lineno;
 
     /* If the line is offscreen, don't even try to display it. */
-    if (row < 0 || row >= editwinrows)
+    if (row < 0 || row >= editwinrows) {
+	statusline(ALERT, "Badness: tried to display a chunk on row %i"
+				" -- please report a bug", row);
 	return 0;
+    }
 
     /* First, blank out the row. */
     blank_row(edit, row, 0, COLS);