From 6957b1aca45c82e976d50c8dc13911284d44743d Mon Sep 17 00:00:00 2001
From: Mika Vilpas <mika.vilpas@gmail.com>
Date: Mon, 16 Jun 2025 21:16:56 +0300
Subject: [PATCH] fix: out-of-bounds error with empty Backstack and `L`
 (`forward`)
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**Issue:**

After starting yazi, and pressing `L` to go forward to the next visited
directory, yazi crashes with the following message:

```rs
❯ RUST_BACKTRACE=full yazi
Backtrace (most recent call first):
  File "<unknown>", line 0, in __mh_execute_header
  File "<unknown>", line 0, in __mh_execute_header
  File "<unknown>", line 0, in __mh_execute_header
  File "<unknown>", line 0, in __mh_execute_header
  File "<unknown>", line 0, in __mh_execute_header
  File "<unknown>", line 0, in __mh_execute_header
  File "<unknown>", line 0, in __mh_execute_header
  File "<unknown>", line 0, in __mh_execute_header
  File "<unknown>", line 0, in __mh_execute_header
  File "<unknown>", line 0, in __mh_execute_header
  File "<unknown>", line 0, in __mh_execute_header
  File "<unknown>", line 0, in __mh_execute_header
  File "<unknown>", line 0, in __mh_execute_header
  File "<unknown>", line 0, in __mh_execute_header
  File "<unknown>", line 0, in __mh_execute_header
  File "<unknown>", line 0, in __mh_execute_header

The application panicked (crashed).
  index out of bounds: the len is 0 but the index is 1
in yazi-core/src/tab/backstack.rs, line 48
thread: main
```

**Solution:**

Fix the out-of-bounds error by accounting for the case where the
`Backstack` is empty.
---
 yazi-core/src/tab/backstack.rs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/yazi-core/src/tab/backstack.rs b/yazi-core/src/tab/backstack.rs
index bb9ffd5e..4bd8afa6 100644
--- a/yazi-core/src/tab/backstack.rs
+++ b/yazi-core/src/tab/backstack.rs
@@ -41,7 +41,7 @@ impl<T: Eq + Clone> Backstack<T> {
 	}
 
 	pub fn shift_forward(&mut self) -> Option<&T> {
-		if self.cursor + 1 == self.stack.len() {
+		if self.cursor + 1 >= self.stack.len() {
 			None
 		} else {
 			self.cursor += 1;
@@ -56,7 +56,9 @@ mod tests {
 
 	#[test]
 	fn test_backstack() {
-		let mut bs = Backstack::default();
+		let mut bs: Backstack<u32> = Backstack::default();
+		assert_eq!(bs.shift_forward(), None);
+
 		bs.push(&1);
 		assert_eq!(bs.stack[bs.cursor], 1);