[Issue 19999] New: compile time logic (pragma, static if) in sub eponymous templates are ignored

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19999

          Issue ID: 19999
           Summary: compile time logic (pragma, static if) in sub
                    eponymous templates are ignored
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: minor
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: davidbennett at bravevision.com

In the below example fun1 compiles fine and outputs 2 "run template constraint"
messages.

However fun2 does not compile and does not output any pragma messages.

```
struct Type(Args...)
{
    alias args = Args;
}

// This works
template fun1(Args...)
{
    pragma(msg, "run template constraint");
    template fun1(T) if(__traits(compiles, { enum _ = T.args; }))
    {
        alias S = Type!(T.args,Args);
        auto fun1(T t){
            S s;
            return s;
        }
    }
}

// This does not
template fun2(Args...)
{
    template fun2(T) 
    {
        pragma(msg, "run static if");
        static if(__traits(compiles, { enum _ = T.args; }))
        {
            alias S = Type!(T.args,Args);
            auto fun2(T t){
                S s;
                return s;
            }
        }

    }
}

void main()
{
    Type!() t;

    auto s1 = t.fun1!(1, 2).fun1!(3, 4);
    assert(s1.args.length == 4);

    auto s2 = t.fun2!(1, 2).fun2!(3, 4);
    assert(s2.args.length == 4);
}
```

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