Iterate all visible symbols, even from imported modules

[Lodovico Giaretta via Digitalmars-d-learn]

As per title, is it possible to iterate all visible symbols of 
the current module and of all imported modules and packages? My 
aim is to find everything in scope that has a specific UDA.

module foo;

import std.stdio, std.array, std.algorithm;

void bar(){}

struct S{}

void main()
{
     // prints ["object", "std", "bar", "S", "main"]
     // how do I discover that "std" is a package?
     writeln([__traits(allMembers, foo)]);


     // prints ["object", "core", "std", "KeepTerminator", 
"GCC_IO", ... ]
     // strange thing: it looks the same even if I remove all 
imports other than std.stdio
     writeln([__traits(allMembers, foo.std)]);
}

Thank you in advance.