Possible incorrect _MSC_VER reference

[ua-code-dragon]

json/single_include/nlohmann/json.hpp

Line 17470 in e7b3b40

#if defined(JSON_HAS_CPP_17) && (defined(__GNUC__) || (defined(_MSC_VER) and _MSC_VER <= 1914))

This condition seems to check "Visual Studio 2017 or later", so there should be >= 1914, not <=

[nlohmann]

This comparison was introduced in #1028 and last changed in #1496. In #1028 (comment), I think the reason is described why it should be <=:

So the bug preventing enabling this feature on msvc has been fixed: https://developercommunity.visualstudio.com/content/problem/243183/stdstring-should-not-have-a-operator-that-takes-a.html

It should be out in 15.8 (msvc 19.15?), so in 19.14 and older it is disabled, as discussed.

[ua-code-dragon]

Maybe I'm wrong, but std::string_view is only available from C++17. For example, Visual Studio 2015 has _MSC_VER=1900, so this #if becomes true and I got an error on unknown string_view.

[nlohmann]

Good point. I'm not using MSVC myself, but I may be able to check via AppVeyor.

[ua-code-dragon]

According to this the N4562 feature set with string_view has been added in VS 2017 15.0
According to this there was _MSC_VER=1910
Maybe the mentioned condition should be ... || (defined(_MSC_VER) and _MSC_VER >= 1910 and _MSC_VER <= 1914))

[garethsb]

Doesn't the check for JSON_HAS_CPP_17 already deal with the beginning of the range?

[dota17]

Doesn't the check for JSON_HAS_CPP_17 already deal with the beginning of the range?

As I can see, the check for JSON_HAS_CPP_17 and _MSC_VER is a parallel relationship(||),
so I agree with @ua-code-dragon in #2112 (comment).