DIP1028 - Rationale for accepting as is

[Johannes T]

On Monday, 25 May 2020 at 00:56:04 UTC, Timon Gehr wrote:
> [..]

After thinking about it, Walter ultimately made the right 
decision, leading to overall higher safety and code quality.
We all agree that making extern C @safe is incorrect. It's also 
meaningless. Even if you were to verify the safety of a specific 
version of your binding, it can't be known what's loaded at 
runtime. It's not the compiler's concern. @safe extern shall be 
an error. We might additionally make an exception and make all 
extern C @system. It would be correct for the declarations, but 
inconsistent in regard to default safety. It doesn't affect the 
outcome. Let's say we'll go with @system, it gives us a bit more 
freedom.
We hit compile, our now safe wrappers are errors. We are most 
likely to do one of two things, depending on the module failing 
to compile. If it mostly wrappers, we slap @trusted: at the top. 
If there are just a few functions calling C, we only annotate 
those with @trusted. Let's be real, we probably won't begin 
checking and annotating the trustworthiness of the C functions. 
An individual programmer might, but not on average.
We are formally correct, but @trusted can't be trusted at this 
point. It has lost its meaning. We now have to check all foreign 
@trusted code, which we probably won't.
We could have moved the problem one level down and slapped 
@trusted: on top of the @system declarations. Now there is a 
bunch of safe code using them. It doesn't change much. @trusted: 
is easier to grep, but we won't put everything down and begin 
trustworthily annotate extern C. So yeah, I do believe Walter was 
right. @safe on extern is formally incorrect but leads to safer 
code because @trusted still has its power.