From 733ce196549696667e09eac8f83d844a5de4713e Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Sat, 13 Apr 2024 20:45:39 -0700
Subject: [PATCH] terminal: handle case where eraseRowBounded happens at top of
 page

Fixes #1677

If eraseRowBounded is called at the top of a page AND there is a tracked
pin at the top of the page, then we'd have an integer overflow. The test
case covers this and this adds a fix.
---
 src/terminal/PageList.zig | 37 +++++++++++++++++++++++++++++++++++--
 1 file changed, 35 insertions(+), 2 deletions(-)

diff --git a/src/terminal/PageList.zig b/src/terminal/PageList.zig
index 6a159d463..1946a84aa 100644
--- a/src/terminal/PageList.zig
+++ b/src/terminal/PageList.zig
@@ -2107,7 +2107,14 @@ pub fn eraseRowBounded(
             const p = p_ptr.*;
             if (p.page == page and
                 p.y >= pn.y and
-                p.y <= pn.y + limit) p.y -= 1;
+                p.y <= pn.y + limit)
+            {
+                if (p.y == 0) {
+                    p.x = 0;
+                } else {
+                    p.y -= 1;
+                }
+            }
         }
 
         return;
@@ -2125,7 +2132,13 @@ pub fn eraseRowBounded(
         var pin_it = self.tracked_pins.keyIterator();
         while (pin_it.next()) |p_ptr| {
             const p = p_ptr.*;
-            if (p.page == page and p.y >= pn.y) p.y -= 1;
+            if (p.page == page and p.y >= pn.y) {
+                if (p.y == 0) {
+                    p.x = 0;
+                } else {
+                    p.y -= 1;
+                }
+            }
         }
     }
 
@@ -4481,6 +4494,26 @@ test "PageList eraseRowBounded less than full row" {
     try testing.expectEqual(@as(usize, 0), p_out.x);
 }
 
+test "PageList eraseRowBounded with pin at top" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+
+    var s = try init(alloc, 80, 10, null);
+    defer s.deinit();
+
+    // Pins
+    const p_top = try s.trackPin(s.pin(.{ .active = .{ .y = 0, .x = 5 } }).?);
+    defer s.untrackPin(p_top);
+
+    // Erase only a few rows in our active
+    try s.eraseRowBounded(.{ .active = .{ .y = 0 } }, 3);
+    try testing.expectEqual(s.rows, s.totalRows());
+
+    try testing.expectEqual(s.pages.first.?, p_top.page);
+    try testing.expectEqual(@as(usize, 0), p_top.y);
+    try testing.expectEqual(@as(usize, 0), p_top.x);
+}
+
 test "PageList eraseRowBounded full rows single page" {
     const testing = std.testing;
     const alloc = testing.allocator;