Is this a bug with __traits(derivedMembers)?

[ag0aep6g]

On Tuesday, 12 June 2018 at 13:40:45 UTC, bauss wrote:
> See the following: https://run.dlang.io/is/uQ21PH
>
> (I have tried with allMembers too.)
>
> It's like it won't pick up the member that is added using a 
> mixin at line 22.
>
> ```
> mixin("ubyte[" ~ to!string(__PADDING_SIZE__) ~ "] __PADDING__" 
> ~ member  ~ ";");
> ```

It's because the identifier starts with two underscores. Such 
identifiers are reserved for internal use, and apparently they're 
ignored by some (all?) __traits.

I'm not sure if this can count as a bug, but it doesn't look just 
fine either.

Smaller test case:

----
struct S
{
     int foo, __bar, baz;
}
pragma(msg, __traits(allMembers, S)); /* tuple("foo", "baz") */
----