A D2 program:

import std.traits: EnumMembers;
enum Foo { A, B }
void main() {
    alias EnumMembers!Foo members; // OK
    enum n1 = members.length; // OK
    enum n2 = (EnumMembers!Foo).length; // line 6, Error
}


DMD 2.051 shows the error:
test.d(6): Error: EnumMembers!(Foo) is used as a type

------------------------

A similar program:

import std.traits: EnumMembers;
enum Foo { A, B }
void main() {
    alias EnumMembers!Foo members;
    enum n = members.length; // OK
    int[n] data1; // OK
    int[members.length] data2; // line 7, ERROR
}


DMD 2.051 shows the errors:
test.d(7): Error: identifier 'length' of 'members.length' is not defined
test.d(7): Error: index is not a type or an expression

I have add a "DMD" tag for the Component of this bug because I am not sure about the cause.