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include/json: check MSVC before adding pragma warning directive #1212

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include/json: check MSVC before adding pragma warning directive #1212

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7 changes: 5 additions & 2 deletions include/json/config.h
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Original file line number Diff line number Diff line change
Expand Up @@ -34,18 +34,21 @@
#if defined(JSON_DLL_BUILD)
#if defined(_MSC_VER) || defined(__MINGW32__)
#define JSON_API __declspec(dllexport)
#define JSONCPP_DISABLE_DLL_INTERFACE_WARNING
#elif defined(__GNUC__) || defined(__clang__)
#define JSON_API __attribute__((visibility("default")))
#endif // if defined(_MSC_VER)

#elif defined(JSON_DLL)
#if defined(_MSC_VER) || defined(__MINGW32__)
#define JSON_API __declspec(dllimport)
#define JSONCPP_DISABLE_DLL_INTERFACE_WARNING
#endif // if defined(_MSC_VER)
#endif // ifdef JSON_DLL_BUILD

// Disable MSVC specific compiler warnings
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This macro used to only get defined when JSON_DLL_BUILD is defined.
I think it should stay that way, as it's clearly only relevant to DLL builds. Move it back up into the preceding #if block.

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But it was defined in both JSON_DLL_BUILD and JSON_DLL sections. What's the issue with current change?

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Sorry, I misread and thought JSON_DLL was nested inside JSON_DLL_BUILD.
So looking at the if/else structure here, we have 3 relevant modes. JSON_DLL, JSON_DLL_BUILD, and everything else.

I think JSONCPP_DISABLE_DLL_INTERFACE_WARNING should only be engaged when we're making a DLL target AND we're using a MSFT compiler. I think we should only disable the warnings when we expect to generate them and need to silence them. We don't need this warning silenced if JSON_API doesn't expand into a dll-related declspec. If we're not building with DLL interface declspecs, we are silencing a warning unnecessarily and we don't need to do that. So I think we should be extremely conservative in turning off warnings. So:

#if defined(_MSC_VER) && (defined (JSON_DLL) || defined(JSON_DLL_BUILD))
#define JSONCPP_DISABLE_DLL_INTERFACE_WARNING
#endif

?

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But JSONCPP_DISABLE_DLL_INTERFACE_WARNING is defined in include/json files. So, if a project includes those header files MSVC compiler shows warnings due to jsoncpp.

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Looping back around to this. I think the confusion is that the warnings you are seeing are NOT DLL_INTERFACE_WARNINGs. This should really be renamed to:

JSONCPP_DISABLE_MSVC_WARNINGS

#if defined(_MSC_VER)
#define JSONCPP_DISABLE_DLL_INTERFACE_WARNING
#endif

#if !defined(JSON_API)
#define JSON_API
#endif
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2 changes: 1 addition & 1 deletion include/json/writer.h
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Expand Up @@ -15,7 +15,7 @@

// Disable warning C4251: <data member>: <type> needs to have dll-interface to
// be used by...
#if defined(JSONCPP_DISABLE_DLL_INTERFACE_WARNING) && defined(_MSC_VER)
#if defined(JSONCPP_DISABLE_DLL_INTERFACE_WARNING)
#pragma warning(push)
#pragma warning(disable : 4251)
#endif // if defined(JSONCPP_DISABLE_DLL_INTERFACE_WARNING)
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