From 8f31c01808aac42ef0aa9970670a1edea8d1ec32 Mon Sep 17 00:00:00 2001
From: Ben Deane <ben@elbeno.com>
Date: Mon, 17 Feb 2025 13:38:54 -0700
Subject: [PATCH] :art: Make `bitset::lowest_unset` work correctly with
 enumerations

---
 include/stdx/bitset.hpp | 6 +++---
 test/bitset.cpp         | 5 +++++
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/stdx/bitset.hpp b/include/stdx/bitset.hpp
index 50ab7b2..c583858 100644
--- a/include/stdx/bitset.hpp
+++ b/include/stdx/bitset.hpp
@@ -341,16 +341,16 @@ class bitset {
         return n + static_cast<std::size_t>(popcount(highbits()));
     }
 
-    [[nodiscard]] constexpr auto lowest_unset() const -> std::size_t {
+    [[nodiscard]] constexpr auto lowest_unset() const {
         std::size_t i = 0;
         for (auto e : storage) {
             if (auto offset = static_cast<std::size_t>(countr_one(e));
                 offset != std::numeric_limits<elem_t>::digits) {
-                return i + offset;
+                return static_cast<iter_arg_t>(i + offset);
             }
             i += std::numeric_limits<elem_t>::digits;
         }
-        return i;
+        return static_cast<iter_arg_t>(i);
     }
 
     [[nodiscard]] constexpr auto operator~() const -> bitset {
diff --git a/test/bitset.cpp b/test/bitset.cpp
index e383ee0..e573cb1 100644
--- a/test/bitset.cpp
+++ b/test/bitset.cpp
@@ -485,6 +485,11 @@ TEST_CASE("use bitset with enum struct (transform_reduce)", "[bitset]") {
                            bs));
 }
 
+TEST_CASE("use bitset with enum struct (lowest_unset)", "[bitset]") {
+    constexpr auto bs = stdx::bitset<Bits::MAX>{stdx::place_bits, Bits::ZERO};
+    CHECK(bs.lowest_unset() == Bits::ONE);
+}
+
 #if __cplusplus >= 202002L
 TEST_CASE("construct with a ct_string", "[bitset]") {
     using namespace stdx::literals;