dip1000 and preview in combine to cause extra safety errors

[jmh530]

On Thursday, 9 June 2022 at 15:38:10 UTC, jmh530 wrote:
> On Thursday, 9 June 2022 at 15:23:35 UTC, Timon Gehr wrote:
>> [snip]
>> There is no upside to allowing this `scope` annotation.
>
> [snip]

Below is also unintuitive as the compiler has all the information 
needed to verify that the reference is escaping. Also, since the 
escape analysis occurs only in @safe functions, it is assumed 
that no escape happens in the @trusted one called by the @safe 
one.

The situation reminds me a little of `restrict` in C. `restrict` 
tells the compiler to make certain assumptions about the code, 
but it is up the programmer to ensure that those assumptions are 
upheld.


```d
int* a;

@safe
void foo(scope int* x) {
     //a = x; //error
     bar(x);
}

@trusted
void bar(scope int* x) {
     a = x;
}

void main() {
     int x = 1;
     foo(&x);
     assert(*a == 1);
}
```