import std.stdio;

struct A
{
    mixin member!(M1, M2);
}

struct M1 {}
struct M2 {}

mixin template member(children...)
{
    static if(children.length)
    {
        children[0] m;
        mixin member!(children[1..$]);
    }
}

void main()
{
    A a;
    writeln(__traits(allMembers, A));
}

-- 

dmd bugrep.d
dmd: dsymbol.c:1052: static int ScopeDsymbol::foreach(Dsymbols*, int (*)(void*, size_t, Dsymbol*), void*, size_t*): Assertion `members' failed.
Aborted

dmd -v
DMD64 D Compiler v2.057
Copyright (c) 1999-2011 by Digital Mars written by Walter Bright
Documentation: http://www.digitalmars.com/d/2.0/index.html