[Issue 22916] New: [dip1000] copy of ref return still treated as scope variable

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22916

          Issue ID: 22916
           Summary: [dip1000] copy of ref return still treated as scope
                    variable
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Keywords: safe
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: dkorpel at live.nl

This came up in a custom dynamic array type of mine.
```
// compile with -preview=dip1000
@safe:
struct Arr
{
    int** ptr;

    ref int* index() return scope {
        return *ptr;
    }

    void assign(int* p) scope {
        *ptr = p;
    }
}

void main()
{
    scope Arr a;
    a.assign(a.index());
}
```

`index` is `return scope` since it returns an element of a scope array by ref.
However, when it's passed to the `assign` function, a copy of the `ref` return
is passed, implicitly dereferencing it so it shouldn't be scope anymore. The
compiler still files this error though:

> Error: scope variable `a` assigned to non-scope parameter `p` calling onlineapp.Arr.assign

--