@system blocks and safer @trusted (ST) functions

[jfondren]

On Sunday, 25 July 2021 at 20:36:09 UTC, claptrap wrote:
>
> So...
>
> Call a safe function and get an int.
> Use that int to index into an array with bounds checking turned 
> off.
>
> Wheres the memory safety bug? In the function that returns the 
> int or in the system code that bypasses bounds checking?
>

The questioner is what's at issue there, not the question.

Questioner #1: someone reviewing a patch that only changes the 
@safe function. This reviewer cannot determine from just the 
changes, to only @safe functions, that they won't cause the 
patched program to develop an out of bounds access. 
@safe/@trusted/@system is not really helping this questioner.

Questioner #2: someone reviewing a program with an out of bounds 
access. This reviewer doesn't have to examine @safe functions 
except when tracing the inputs to a @system block/function where 
they isolated the error. @safe/@trusted/@system has potentially 
saved this questioner a lot of time with getting an answer to 
"Where's the memory safety bug?"