Make NativeCall complain about the declaration of CPointers with attributes.

[JJ]

The Problem

NativeCall does not complain when a CPointer has some internal structure. For instance

class p_timespec is repr('CPointer') {
    has uint32 $.tv_sec;
    has long $.tv_nanosecs;
}

Expected Behavior

CPointers shouldn't have any internal structure, and CStructs are actually pointers to that. So it should probably issue some helpful hint that what you're looking for is actually CStruct.

Actual Behavior

You can use it alright, it coredumps without any error mesage.

Steps to Reproduce

Run this

use v6;

use NativeCall;

class p_timespec is repr('CPointer') {
    has uint32 $.tv_sec;
    has long $.tv_nanosecs;
}
    
sub clock_gettime(uint32 $clock-id, p_timespec $tspec --> uint32) is native(Str) { * };

my p_timespec $this-time .=new;

my $result = clock_gettime( 0, $this-time);

say "$result, $this-time";

Result:

[3]    29411 segmentation fault (core dumped)  perl6 --ll-exception is-repr.p6

Environment

I'm using perl6 2018.03 in Ubuntu 14.04.

[lizmat]

Perhaps some way to check / complain about such a situation in ClassHOW.compose?