I think this should be allowed, aswell as implementing forward declared enums and structs (IIRC the compiler even has some error messages that suggest that it is intended).

As a workaround, you could put your prototypes into a struct and generate the declarations for the static linking and the stubs for dynamic linking from their declarations and run your magic on the members of "prototypes":

struct prototypes
{
        void fun1(int a, int b);
        void fun2(int a, int b);
}

mixin(magic([__traits(allMembers, prototypes)])


That way you don't put the symbols into the same scope as the prototypes, and you will not add new symbols to the same scope that you are iterating over.