From a0f5dbc05d399a39e575ba176e2f048aecde02c1 Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Fri, 23 Jun 2023 10:59:52 +0100
Subject: [PATCH] tor-circmgr: random_idx_where: Don't panic on empty range

Fixes #918.
---
 crates/tor-circmgr/src/hspool/pool.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/crates/tor-circmgr/src/hspool/pool.rs b/crates/tor-circmgr/src/hspool/pool.rs
index ec60fafe1..21d2f031d 100644
--- a/crates/tor-circmgr/src/hspool/pool.rs
+++ b/crates/tor-circmgr/src/hspool/pool.rs
@@ -144,6 +144,9 @@ where
     P: Fn(&T) -> bool,
 {
     let n_circuits = slice.len();
+    if n_circuits == 0 {
+        return None;
+    }
     let shift = rng.gen_range(0..n_circuits);
     (shift..n_circuits)
         .chain(0..shift)