// our header.h which is used by entire program
struct ZeStruct;
int ZeStruct_x(ZeStruct* z);

// some library which we want to hide from the world
struct ConcreteZeStruct { int x; };

// implementation that tries to hide ConcreteZeStruct behind ZeStruct?
typedef struct ConcreteZeStruct ZeStruct;

int ZeStruct_x(ZeStruct* z){
  return z->x;
}

Line 9: error: conflicting declaration 'typedef struct ConcreteZeStruct ZeStruct'
compilation terminated due to -Wfatal-errors.