[Dlang-internal] DIP1000 discussion and testing

[Walter Bright via Dlang-internal]

On 12/17/2016 7:38 AM, Mathias Lang wrote:
> void main () @safe
> {
>     int[] a = escape();
> }
>
> int[] escape () @safe
> {
>     Foo f;
>     return f.foo;
> }
>
> struct Foo
> {
>     int[10] v;
>     int[] foo () return @safe { return this.v; }
> }

I've said it's all about pointers and addresses. So let's remove the 
abstractions, and rewrite it in the equivalent pointers and addresses form:

```
void main () @safe
{
     int* a = escape();
}

int* escape () @safe
{
     int f;
     return foo(f);  // Error: escaping reference to local variable f
}

int* foo (return ref int i) @safe { return &i; }
```

and indeed it does fail to compile. So the bug in the compiler is failing to 
recognize the abstract version of the pointers and addresses logic.