Is this a bug with __traits(derivedMembers)?

[Bauss]

On Tuesday, 12 June 2018 at 14:37:19 UTC, ag0aep6g wrote:
> 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") */
> ----
Thank you. I was not aware of such a gotcha.

Should definitely be documented or yield an error/warning if 
attempted in user code else you end up with hidden "bugs" like 
this