From e113b204156a5503971341acef0717276e1eef52 Mon Sep 17 00:00:00 2001
From: Niels Lohmann <mail@nlohmann.me>
Date: Wed, 29 Dec 2021 20:24:06 +0100
Subject: [PATCH] :rotating_light: fix warning (code taken from #2736)

---
 include/nlohmann/detail/output/serializer.hpp | 16 ++++++++++++++--
 single_include/nlohmann/json.hpp              | 16 ++++++++++++++--
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/include/nlohmann/detail/output/serializer.hpp b/include/nlohmann/detail/output/serializer.hpp
index e87990d852..7cce7d5c7c 100644
--- a/include/nlohmann/detail/output/serializer.hpp
+++ b/include/nlohmann/detail/output/serializer.hpp
@@ -664,6 +664,19 @@ class serializer
         }
     }
 
+    // templates to avoid warnings about useless casts
+    template <typename NumberType, enable_if_t<std::is_signed<NumberType>::value, int> = 0>
+    bool is_negative_number(NumberType x)
+    {
+        return x < 0;
+    }
+
+    template < typename NumberType, enable_if_t <std::is_unsigned<NumberType>::value, int > = 0 >
+    bool is_negative_number(NumberType /*unused*/)
+    {
+        return false;
+    }
+
     /*!
     @brief dump an integer
 
@@ -707,12 +720,11 @@ class serializer
         // use a pointer to fill the buffer
         auto buffer_ptr = number_buffer.begin(); // NOLINT(llvm-qualified-auto,readability-qualified-auto,cppcoreguidelines-pro-type-vararg,hicpp-vararg)
 
-        const bool is_negative = std::is_signed<NumberType>::value && !(x >= 0); // see issue #755
         number_unsigned_t abs_value;
 
         unsigned int n_chars{};
 
-        if (is_negative)
+        if (is_negative_number(x))
         {
             *buffer_ptr = '-';
             abs_value = remove_sign(static_cast<number_integer_t>(x));
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index f2c79b4bfd..92aa8aef06 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -16707,6 +16707,19 @@ class serializer
         }
     }
 
+    // templates to avoid warnings about useless casts
+    template <typename NumberType, enable_if_t<std::is_signed<NumberType>::value, int> = 0>
+    bool is_negative_number(NumberType x)
+    {
+        return x < 0;
+    }
+
+    template < typename NumberType, enable_if_t <std::is_unsigned<NumberType>::value, int > = 0 >
+    bool is_negative_number(NumberType /*unused*/)
+    {
+        return false;
+    }
+
     /*!
     @brief dump an integer
 
@@ -16750,12 +16763,11 @@ class serializer
         // use a pointer to fill the buffer
         auto buffer_ptr = number_buffer.begin(); // NOLINT(llvm-qualified-auto,readability-qualified-auto,cppcoreguidelines-pro-type-vararg,hicpp-vararg)
 
-        const bool is_negative = std::is_signed<NumberType>::value && !(x >= 0); // see issue #755
         number_unsigned_t abs_value;
 
         unsigned int n_chars{};
 
-        if (is_negative)
+        if (is_negative_number(x))
         {
             *buffer_ptr = '-';
             abs_value = remove_sign(static_cast<number_integer_t>(x));