@system blocks and safer @trusted (ST) functions

[Paul Backus]

On Sunday, 25 July 2021 at 13:55:14 UTC, Bruce Carneal wrote:
> The improvements on the status quo include the ability to 
> easily delimit "should check *very* closely" code and the 
> corresponding ability to engage @safety checking on any 
> remainder.

We already have this ability: simply avoid writing `@trusted` 
code whose safety depends on out-of-band knowledge about `@safe` 
code, and enforce this practice via code review.

As I've discussed previously [1], there is no way to enforce this 
at the language level, because the language does not (and cannot 
possibly) know what knowledge `@trusted` code depends on for its 
memory safety.

[1] 
https://forum.dlang.org/post/auqcjtbbamviembvcaps@forum.dlang.org