Exception.toString not useable in @safe

[braddr]

This code (extracted from a larger project):

module safety;

import core.sys.posix.stdio : printf;
import std.exception;

void main() @safe
{
    try
    {
        throw new Exception("irrelevant");
    }
    catch (Exception e)
    {
        string s = e.toString();
    }
}

Results in:

safety.d(14): Error: `@safe` function `D main` cannot call `@system` function `object.Throwable.toString`
/home/braddr/sandbox/dmd.2.109.1/linux/bin64/../../src/druntime/import/object.d(2652):        `object.Throwable.toString` is declared here

[0xEAB]

@braddr transferred this issue from dlang/dmd Dec 18, 2024

Isn’t this rather a druntime thing than a Phobos one?

[thewilsonator]

Yes

[braddr]

oops.. forgot that druntime was moved to the dmd repo. I moved it out since it wasn't a dmd issue, but you're correct.

[jmdavis]

Yeah, this falls under the general set of issues that come from these functions being on Object - and being there from before @safe was even a thing to boot - though even if Object didn't have it, Exception would then have to introduce it into its own hierarchy, and that creates some of the same problems.

If we made toString be @safe, then that would break existing code. It would also force all implementations to be @safe or @trusted - which may not be unreasonable, but I don't think that we can make that change at this point. We may be able to change it with editions at some point, though attributes are always going to be a problem in a situation like this, since putting them on the base class function puts restrictions on the entire class hierarchy - which is probably reasonable in the case of @safe but considerably less so with most of the others.