First Draft: Making printf @safe

[Nick Treleaven]

On Saturday, 3 August 2024 at 15:28:35 UTC, Tim wrote:
> One alternative would be a wrapper around printf, which checks 
> the format string at compile time and modifies it and other 
> parameters, so they match. It could look something like this:
>
> ```D
> void printfWrapper(string fmt, P...)(P params) @trusted
> {
>     // ...
> }
>
> void main() @safe
> {
>     string s = "World";
>     printfWrapper!"Hello %s\n"(s);
> }
> ```

There are 13 `pragma(printf)` functions in dmd. They could be 
changed. However, now those aren't functions but templates. I'm 
not sure if that's OK for ldc and gdc, maybe. And every call to 
each of those functions would need updating (unless we had enum 
parameters). The dmd as a library API would also be impacted, 
even if the original functions were kept as deprecated.

> An advantage would be, that it could be used immediately in 
> DMD. A new language feature could only be used after the 
> bootstrap compiler is updated to this version, too.

Those functions could maybe be marked @trusted on the basis that 
the current dmd tests with the feature have checked all calls to 
them, and dmd as a library could require the new version of dmd 
for the API with the new @trusted functions.