[Issue 20695] New: Copy constructor disable default struct constructor

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20695

          Issue ID: 20695
           Summary: Copy constructor disable default struct constructor
           Product: D
           Version: D2
          Hardware: x86
                OS: Mac OS X
            Status: NEW
          Keywords: C++, rejects-valid
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: pro.mathias.lang at gmail.com

```
struct Bar
{
    this(const ref Bar o) {}

    string a;
    uint b;
}

void main ()
{
    // foo.d(11): Error: struct Bar has constructors, cannot use { initializers
}, use Bar( initializers ) instead
    Bar b = { a: "Hello", b: 42 };
    // foo.d(12): Error: copy constructor foo.Bar.this(ref const(Bar) o) is not
callable using argument types (string\
, int)
    // foo.d(12):        cannot pass rvalue argument "Hello" of type string to
parameter ref const(Bar) o
    Bar c = Bar("Hello", 42);
}
```

Expected result: This should compile. It should also work if the constructor is
`@disable`d.

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