[Issue 13372] traits parent does not work on eponymous templates

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=13372

--- Comment #3 from b2.temp at gmx.com ---
Strangely enough this bug can lead to think that we can detect an eponymous
template:

==========
template isTemplateInstance(alias T : Base!Args, alias Base, Args...)
{
    enum isTemplateInstance = is(typeof(T));
}

template isTemplateInstance(T : Base!Args, alias Base, Args...)
{
    enum isTemplateInstance = is(T);
}

template isTemplateInstance(T)
{
    enum isTemplateInstance = false;
}

template isTemplateInstance(alias T)
{
    enum isTemplateInstance = isTemplateInstance!(typeof(T));
}

template isEponymousTemplate(T)
{
    static if (is(T == class) || is(T == interface) || is(T == struct) || is(T
== union))
    {
        enum p = __traits(parent, T).stringof == T.stringof;
        enum isEponymousTemplate = p && isTemplateInstance!T;
    }
    else
        enum isEponymousTemplate = false;
}

unittest
{
    class A(T){}
    struct B(T){}
    static assert(isEponymousTemplate!(A!int));
    static assert(isEponymousTemplate!(B!int));
    static assert(!isEponymousTemplate!int);
    template C(T)
    {
        class C{}
    }
    static assert(isEponymousTemplate!(C!int));
}

unittest
{
    template A(T)
    {
        class A{}
    }
    static assert(isEponymousTemplate!(A!int));

    template B(T)
    {
        class A{}
    }
    static assert(!isEponymousTemplate!(B!int.A));

    class C(T){}
    static assert(!isEponymousTemplate!int);

    A!int a;
    static assert(isEponymousTemplate!a);
}
==========

Indeed we can detect it but we can't get the parent !
What's happen is that "isEponymousTemplate" yield true for an eponymous
template because the template itself points to its argument !

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