From f1e34070d2966f8794b79fe85fb3c8cae868c48a Mon Sep 17 00:00:00 2001
From: Florian Albrechtskirchinger <falbrechtskirchinger@gmail.com>
Date: Sun, 7 Aug 2022 13:50:08 +0200
Subject: [PATCH] Fix 'const' qualifier on bool& has no effect (#3678)

* Fix 'const' qualifier on bool& has no effect

Thanks, @georgthegreat, for pointing out this issue.

* Extend std::vector<bool> unit test
---
 include/nlohmann/detail/conversions/to_json.hpp | 12 +++++++++---
 single_include/nlohmann/json.hpp                | 12 +++++++++---
 tests/src/unit-constructor1.cpp                 | 11 ++++++++++-
 3 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/include/nlohmann/detail/conversions/to_json.hpp b/include/nlohmann/detail/conversions/to_json.hpp
index ba24c118d..f10a7393e 100644
--- a/include/nlohmann/detail/conversions/to_json.hpp
+++ b/include/nlohmann/detail/conversions/to_json.hpp
@@ -267,9 +267,15 @@ inline void to_json(BasicJsonType& j, T b) noexcept
     external_constructor<value_t::boolean>::construct(j, b);
 }
 
-template<typename BasicJsonType,
-         enable_if_t<std::is_convertible<const std::vector<bool>::reference&, typename BasicJsonType::boolean_t>::value, int> = 0>
-inline void to_json(BasicJsonType& j, const std::vector<bool>::reference& b) noexcept
+template < typename BasicJsonType, typename BoolRef,
+           enable_if_t <
+               ((std::is_same<std::vector<bool>::reference, BoolRef>::value
+                 && !std::is_same <std::vector<bool>::reference, typename BasicJsonType::boolean_t&>::value)
+                || (std::is_same<std::vector<bool>::const_reference, BoolRef>::value
+                    && !std::is_same <detail::uncvref_t<std::vector<bool>::const_reference>,
+                                      typename BasicJsonType::boolean_t >::value))
+               && std::is_convertible<const BoolRef&, typename BasicJsonType::boolean_t>::value, int > = 0 >
+inline void to_json(BasicJsonType& j, const BoolRef& b) noexcept
 {
     external_constructor<value_t::boolean>::construct(j, static_cast<typename BasicJsonType::boolean_t>(b));
 }
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index beee0136c..6668a173b 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -5500,9 +5500,15 @@ inline void to_json(BasicJsonType& j, T b) noexcept
     external_constructor<value_t::boolean>::construct(j, b);
 }
 
-template<typename BasicJsonType,
-         enable_if_t<std::is_convertible<const std::vector<bool>::reference&, typename BasicJsonType::boolean_t>::value, int> = 0>
-inline void to_json(BasicJsonType& j, const std::vector<bool>::reference& b) noexcept
+template < typename BasicJsonType, typename BoolRef,
+           enable_if_t <
+               ((std::is_same<std::vector<bool>::reference, BoolRef>::value
+                 && !std::is_same <std::vector<bool>::reference, typename BasicJsonType::boolean_t&>::value)
+                || (std::is_same<std::vector<bool>::const_reference, BoolRef>::value
+                    && !std::is_same <detail::uncvref_t<std::vector<bool>::const_reference>,
+                                      typename BasicJsonType::boolean_t >::value))
+               && std::is_convertible<const BoolRef&, typename BasicJsonType::boolean_t>::value, int > = 0 >
+inline void to_json(BasicJsonType& j, const BoolRef& b) noexcept
 {
     external_constructor<value_t::boolean>::construct(j, static_cast<typename BasicJsonType::boolean_t>(b));
 }
diff --git a/tests/src/unit-constructor1.cpp b/tests/src/unit-constructor1.cpp
index f294e5cd6..9e62a09f8 100644
--- a/tests/src/unit-constructor1.cpp
+++ b/tests/src/unit-constructor1.cpp
@@ -454,10 +454,19 @@ TEST_CASE("constructors")
             CHECK(j.type() == json::value_t::boolean);
         }
 
-        SECTION("from std::vector<bool>::refrence")
+        SECTION("from std::vector<bool>::reference")
         {
             std::vector<bool> v{true};
             json j(v[0]);
+            CHECK(std::is_same<decltype(v[0]), std::vector<bool>::reference>::value);
+            CHECK(j.type() == json::value_t::boolean);
+        }
+
+        SECTION("from std::vector<bool>::const_reference")
+        {
+            const std::vector<bool> v{true};
+            json j(v[0]);
+            CHECK(std::is_same<decltype(v[0]), std::vector<bool>::const_reference>::value);
             CHECK(j.type() == json::value_t::boolean);
         }
     }