In Go 1.15.3 and later, cgo will not permit Go code to allocate an

undefined struct type (a C struct defined as just <code>struct

S;</code> or similar) on the stack or heap.

Go code will only be permitted to use pointers to those types.

Allocating an instance of such a struct and passing a pointer, or a

full struct value, to C code was always unsafe and unlikely to work

correctly; it is now forbidden.

The fix is to either rewrite the Go code to use only pointers, or to

ensure that the Go code sees the full definition of the struct by

including the appropriate C header file.