Merge branch 'develop' of https://github.com/nlohmann/json into develop

test/src/unit-udt.cpp

@@ -692,3 +692,22 @@ TEST_CASE("custom serializer that does adl by default", "[udt]")
     CHECK(me == j.get<udt::person>());
     CHECK(me == cj.get<udt::person>());
 }
+
+namespace
+{
+struct incomplete;
+
+// std::is_constructible is broken on macOS' libc++
+// use the cppreference implementation
+
+template <typename T, typename = void>
+struct is_constructible_patched : std::false_type {};
+
+template <typename T>
+struct is_constructible_patched<T, decltype(void(json(std::declval<T>())))> : std::true_type {};
+}
+
+TEST_CASE("an incomplete type does not trigger a compiler error in non-evaluated context", "[udt]")
+{
+    static_assert(not is_constructible_patched<json, incomplete>::value, "");
+}