message: to/from_json: add a MSVC-specific static_assert to force a stacktrace
diff: @@ -1351,6 +1351,13 @@ struct to_json_fn
  {
  static_assert(sizeof(BasicJsonType) == 0,
  "could not find to_json() method in T's namespace");
  +
  +#ifdef _MSC_VER
  + // Visual Studio does not show a stacktrace for the above assert.
  + using decayed = uncvref_t<T>;
  + static_assert(sizeof(typename decayed::force_msvc_stacktrace) == 0,
  + "forcing msvc stacktrace to show which T we're talking about.");
  +#endif
  }
  public:
  @@ -1378,6 +1385,12 @@ struct from_json_fn
  {
  static_assert(sizeof(BasicJsonType) == 0,
  "could not find from_json() method in T's namespace");
  +#ifdef _MSC_VER
  + // Visual Studio does not show a stacktrace for the above assert.
  + using decayed = uncvref_t<T>;
  + static_assert(sizeof(typename decayed::force_msvc_stacktrace) == 0,
  + "forcing msvc stacktrace to show which T we're talking about.");
  +#endif
  }
  public:
  