Is this a bug with __traits(derivedMembers)?

[bauss]

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  ~ ";");
```

As you can see if you take sizeof from the struct then it gets 
the correct size, so it's like the member exists, but you cannot 
retrieve it with traits.

It's possible to retrieve it manually, so yeah...

If it's a bug then I will file an issue unless someone else will 
do so.

If it's not a bug, then what's going on and what would the 
correct solution be?