[Dlang-internal] DIP1000 discussion and testing

[Mathias Lang via Dlang-internal]

Now that we have https://github.com/dlang/dmd/pull/6253 I came 
back to test it a bit.

First I have a question: What is going to happen with `scope foo 
= new Object` ?
Are we keeping it the way it currently is ? It's something we 
highly rely on at work and it looks like it could work nicely 
with the enhancements, but it wasn't mentioned anywhere.

And from a quick test (Using `-dip25 -transition=safe` and 
5928249 which is the commit of this P.R.), the following code:

```
void main () @safe
{
     scope o = new Object();
}
```

Results in the following error:
scope2.d(3): Error: delete o is not @safe but is used in @safe 
function main

Which works with the compiler I'm currently using, 2.071.2.

By the way, I reiterate my point that tying `scope` verification 
to `@safe` function is highly misleading and not necessary. I 
originally crafted a couple of test case, and when everything 
worked, I was left puzzled for a minute before realizing I forgot 
`@safe`.

Second point, on testing your P.R., I found that the following 
code compiles:

```
alias FunDG = void delegate () @safe;

void main () @safe
{
     int x = 42;
     scope FunDG f = () { assert(x == 42); };
     return fun(&f);
}

FunDG fun (scope FunDG* ptr) @safe
{
     return *ptr;
}
```

As well as the following:
```
alias FunDG = void* delegate () @safe;

void main () @safe
{
     void* x = fwd();
}

void* fwd () @safe
{
     int x = 42;
     scope FunDG f = () { return &x; };
     return fun(f);
}

void* fun (scope FunDG ptr) @safe
{
     return ptr();
}
```

I'm not quite sure how one would express taking a pointer to a 
scope value though.