Merge pull request #2902 from nlohmann/issue2893

Fix useless-cast warnings

cmake/ci.cmake

@@ -356,7 +356,7 @@ set(GCC_CXXFLAGS "-std=c++11                          \
     -Wunused-result                                   \
     -Wunused-value                                    \
     -Wunused-variable                                 \
-    -Wno-useless-cast                                    \
+    -Wuseless-cast                                    \
     -Wvarargs                                         \
     -Wvariadic-macros                                 \
     -Wvector-operation-performance                    \

include/nlohmann/detail/input/binary_reader.hpp

@@ -19,6 +19,7 @@
 #include <nlohmann/detail/input/lexer.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
 #include <nlohmann/detail/meta/is_sax.hpp>
+#include <nlohmann/detail/meta/type_traits.hpp>
 #include <nlohmann/detail/value_t.hpp>
 
 namespace nlohmann
@@ -631,7 +632,7 @@ class binary_reader
             case 0x9B: // array (eight-byte uint64_t for n follow)
             {
                 std::uint64_t len{};
-                return get_number(input_format_t::cbor, len) && get_cbor_array(static_cast<std::size_t>(len), tag_handler);
+                return get_number(input_format_t::cbor, len) && get_cbor_array(detail::conditional_static_cast<std::size_t>(len), tag_handler);
             }
 
             case 0x9F: // array (indefinite length)
@@ -685,7 +686,7 @@ class binary_reader
             case 0xBB: // map (eight-byte uint64_t for n follow)
             {
                 std::uint64_t len{};
-                return get_number(input_format_t::cbor, len) && get_cbor_object(static_cast<std::size_t>(len), tag_handler);
+                return get_number(input_format_t::cbor, len) && get_cbor_object(detail::conditional_static_cast<std::size_t>(len), tag_handler);
             }
 
             case 0xBF: // map (indefinite length)

include/nlohmann/detail/meta/type_traits.hpp

@@ -435,5 +435,19 @@ struct is_constructible_tuple : std::false_type {};
 
 template<typename T1, typename... Args>
 struct is_constructible_tuple<T1, std::tuple<Args...>> : conjunction<is_constructible<T1, Args>...> {};
+
+// to avoid useless casts (see https://github.com/nlohmann/json/issues/2893#issuecomment-889152324)
+template < typename T, typename U, enable_if_t < !std::is_same<T, U>::value, int > = 0 >
+T conditional_static_cast(U value)
+{
+    return static_cast<T>(value);
+}
+
+template<typename T, typename U, enable_if_t<std::is_same<T, U>::value, int> = 0>
+T conditional_static_cast(U value)
+{
+    return value;
+}
+
 }  // namespace detail
 }  // namespace nlohmann

single_include/nlohmann/json.hpp

@@ -3835,6 +3835,20 @@ struct is_constructible_tuple : std::false_type {};
 
 template<typename T1, typename... Args>
 struct is_constructible_tuple<T1, std::tuple<Args...>> : conjunction<is_constructible<T1, Args>...> {};
+
+// to avoid useless casts (see https://github.com/nlohmann/json/issues/2893#issuecomment-889152324)
+template < typename T, typename U, enable_if_t < !std::is_same<T, U>::value, int > = 0 >
+T conditional_static_cast(U value)
+{
+    return static_cast<T>(value);
+}
+
+template<typename T, typename U, enable_if_t<std::is_same<T, U>::value, int> = 0>
+T conditional_static_cast(U value)
+{
+    return value;
+}
+
 }  // namespace detail
 }  // namespace nlohmann
 
@@ -8240,6 +8254,8 @@ struct is_sax_static_asserts
 }  // namespace detail
 }  // namespace nlohmann
 
+// #include <nlohmann/detail/meta/type_traits.hpp>
+
 // #include <nlohmann/detail/value_t.hpp>
 
 
@@ -8853,7 +8869,7 @@ class binary_reader
             case 0x9B: // array (eight-byte uint64_t for n follow)
             {
                 std::uint64_t len{};
-                return get_number(input_format_t::cbor, len) && get_cbor_array(static_cast<std::size_t>(len), tag_handler);
+                return get_number(input_format_t::cbor, len) && get_cbor_array(detail::conditional_static_cast<std::size_t>(len), tag_handler);
             }
 
             case 0x9F: // array (indefinite length)
@@ -8907,7 +8923,7 @@ class binary_reader
             case 0xBB: // map (eight-byte uint64_t for n follow)
             {
                 std::uint64_t len{};
-                return get_number(input_format_t::cbor, len) && get_cbor_object(static_cast<std::size_t>(len), tag_handler);
+                return get_number(input_format_t::cbor, len) && get_cbor_object(detail::conditional_static_cast<std::size_t>(len), tag_handler);
             }
 
             case 0xBF: // map (indefinite length)

test/src/unit-class_parser.cpp

@@ -1381,7 +1381,7 @@ TEST_CASE("parser class")
                 case ('r'):
                 case ('t'):
                 {
-                    CHECK(json::parser(nlohmann::detail::input_adapter(std::string(s))).accept());
+                    CHECK(json::parser(nlohmann::detail::input_adapter(s)).accept());
                     break;
                 }
 
@@ -1394,7 +1394,7 @@ TEST_CASE("parser class")
                 // any other combination of backslash and character is invalid
                 default:
                 {
-                    CHECK(json::parser(nlohmann::detail::input_adapter(std::string(s))).accept() == false);
+                    CHECK(json::parser(nlohmann::detail::input_adapter(s)).accept() == false);
                     break;
                 }
             }
@@ -1445,35 +1445,35 @@ TEST_CASE("parser class")
                 std::string s = "\"\\u";
 
                 // create a string with the iterated character at each position
-                auto s1 = s + "000" + std::string(1, static_cast<char>(c)) + "\"";
-                auto s2 = s + "00" + std::string(1, static_cast<char>(c)) + "0\"";
-                auto s3 = s + "0" + std::string(1, static_cast<char>(c)) + "00\"";
-                auto s4 = s + std::string(1, static_cast<char>(c)) + "000\"";
+                const auto s1 = s + "000" + std::string(1, static_cast<char>(c)) + "\"";
+                const auto s2 = s + "00" + std::string(1, static_cast<char>(c)) + "0\"";
+                const auto s3 = s + "0" + std::string(1, static_cast<char>(c)) + "00\"";
+                const auto s4 = s + std::string(1, static_cast<char>(c)) + "000\"";
 
                 if (valid(c))
                 {
                     CAPTURE(s1)
-                    CHECK(json::parser(nlohmann::detail::input_adapter(std::string(s1))).accept());
+                    CHECK(json::parser(nlohmann::detail::input_adapter(s1)).accept());
                     CAPTURE(s2)
-                    CHECK(json::parser(nlohmann::detail::input_adapter(std::string(s2))).accept());
+                    CHECK(json::parser(nlohmann::detail::input_adapter(s2)).accept());
                     CAPTURE(s3)
-                    CHECK(json::parser(nlohmann::detail::input_adapter(std::string(s3))).accept());
+                    CHECK(json::parser(nlohmann::detail::input_adapter(s3)).accept());
                     CAPTURE(s4)
-                    CHECK(json::parser(nlohmann::detail::input_adapter(std::string(s4))).accept());
+                    CHECK(json::parser(nlohmann::detail::input_adapter(s4)).accept());
                 }
                 else
                 {
                     CAPTURE(s1)
-                    CHECK(json::parser(nlohmann::detail::input_adapter(std::string(s1))).accept() == false);
+                    CHECK(json::parser(nlohmann::detail::input_adapter(s1)).accept() == false);
 
                     CAPTURE(s2)
-                    CHECK(json::parser(nlohmann::detail::input_adapter(std::string(s2))).accept() == false);
+                    CHECK(json::parser(nlohmann::detail::input_adapter(s2)).accept() == false);
 
                     CAPTURE(s3)
-                    CHECK(json::parser(nlohmann::detail::input_adapter(std::string(s3))).accept() == false);
+                    CHECK(json::parser(nlohmann::detail::input_adapter(s3)).accept() == false);
 
                     CAPTURE(s4)
-                    CHECK(json::parser(nlohmann::detail::input_adapter(std::string(s4))).accept() == false);
+                    CHECK(json::parser(nlohmann::detail::input_adapter(s4)).accept() == false);
                 }
             }
         }