https://issues.dlang.org/show_bug.cgi?id=13087
--- Comment #1 from Kenji Hara <k.hara.pg at gmail.com> ---
Reduced test case:
struct Vec
{
    int x;
    void foo() const   // const is necessary
    {
        auto n = component!(this, 'x');
    }
}
template component(alias vec, char c)
{
    alias component = vec.x;
}
--