Using Sundials in a C++20 program results in no clean way to instantiate custom SUNLinearSolvers (and other obejcts).

The usual

struct _generic_SUNLinearSolver_Ops LSOps =·
{
.gettype = SunLinSolWrapper::LSGetType,
.getid = SunLinSolWrapper::LSGetID,
.setatimes = nullptr, ...
};

Isn't permitted because the default constructor makes _generic_SUNLinearSolver_Ops a non-aggregate type.

From include/sundials/sundials_linearsolver.h:127

#ifdef __cplusplus
  _generic_SUNLinearSolver_Ops() = default;
#endif

Removing this default constructor results in a pure aggregate type and declaring the default constructor should not be necessary.

I know this is low priority, but flagging this as usage of C++20 will only increase.