Squelch MSVC warning exporting subclasses of runtime_error (fix for PR …

…#1433) (#1470)

* Squelch MSVC warning exporting subclasses of runtime_error

When compiling {fmt} as a DLL, MSVC complains that we are exporting
classes that inherit from "std::runtime_error", which we are not
exporting.

In this case, it's not really a problem because that symbol is already
exported via the C++ stdlib. So we just add a pragma to silence the
warning.

* Fix compilation with MinGW

Commit 3bc28fc ("Squelch MSVC warning exporting subclasses of
runtime_error", 2019-11-29) silenced a MSVC warning under. The MinGW
compiler also defines _WIN32, but does not support the "warning" pragma.

Introduce a helper macro to squelch the MSVC warning only when using the
Microsoft compiler.

Signed-off-by: Beat Bolli <[email protected]>

* Fix compilation with VS2015 (#1450)

VS2015 does not support the __pragma(...) syntax in the midst of a
class declaration, so move it to just before the declaration.

include/fmt/core.h

@@ -166,13 +166,22 @@
 #endif
 
 #if !defined(FMT_HEADER_ONLY) && defined(_WIN32)
+#  if FMT_MSC_VER
+#    define FMT_NO_W4275 __pragma(warning(suppress : 4275))
+#  else
+#    define FMT_NO_W4275
+#  endif
+#  define FMT_CLASS_API FMT_NO_W4275
 #  ifdef FMT_EXPORT
 #    define FMT_API __declspec(dllexport)
 #  elif defined(FMT_SHARED)
 #    define FMT_API __declspec(dllimport)
 #    define FMT_EXTERN_TEMPLATE_API FMT_API
 #  endif
 #endif
+#ifndef FMT_CLASS_API
+#  define FMT_CLASS_API
+#endif
 #ifndef FMT_API
 #  define FMT_API
 #endif

include/fmt/format.h

@@ -696,6 +696,7 @@ using memory_buffer = basic_memory_buffer<char>;
 using wmemory_buffer = basic_memory_buffer<wchar_t>;
 
 /** A formatting error such as invalid format string. */
+FMT_CLASS_API
 class FMT_API format_error : public std::runtime_error {
  public:
   explicit format_error(const char* message) : std::runtime_error(message) {}
@@ -2707,6 +2708,7 @@ class arg_formatter : public internal::arg_formatter_base<Range> {
  An error returned by an operating system or a language runtime,
  for example a file opening error.
 */
+FMT_CLASS_API
 class FMT_API system_error : public std::runtime_error {
  private:
   void init(int err_code, string_view format_str, format_args args);