dip1000 and preview in combine to cause extra safety errors

[Timon Gehr]

On 09.06.22 16:46, Dennis wrote:
> On Thursday, 9 June 2022 at 01:18:30 UTC, Steven Schveighoffer wrote:
>> For some reason, while you can't return a pointer to a local, you can 
>> return a scope pointer.
> 
> A pointer to a local is guaranteed to be a dangling pointer when you 
> return it, while a `scope` pointer is not guaranteed to be memory with 
> limited lifetime when you return it. `scope` is only a conservative 
> compile-time approximation of what's actually happening, which makes it 
> susceptible to false positives:
> 
> ```D
> int* f(int x) @safe {
>      int* p = &x; // p is inferred scope here
>      p = new int; // p is no longer pointing to stack memory
>      return p;    // Error: scope variable `p` may not be returned
> }
> ```
> This function could be permitted as @system or @trusted code.

Sure, and it should be. But the example was this:

```d
int* foo(scope int* s){ return s; }
```

There is no upside to allowing this `scope` annotation.