ImportC and nothrow/@nogc?

[Paulo Pinto]

On Tuesday, 20 August 2024 at 00:30:46 UTC, Richard (Rikki) 
Andrew Cattermole wrote:
>
> On 20/08/2024 12:24 PM, Gregor Mückl wrote:
>> On Sunday, 18 August 2024 at 09:42:16 UTC, Nicholas Wilson 
>> wrote:
>>> On Sunday, 18 August 2024 at 04:43:34 UTC, Manu wrote:
>>>> [...]
>>>
>>> Well, C may call C++ which may throw. It is very unlikely to 
>>> call the GC however.
>>>
>>> I don't think it would be hard to add a switch that 
>>> "`extern(C)` functions being called from import C are 
>>> `@nogc`".
>> 
>> Here's what I'm thinking:
>> 
>> The C function interface has no notion of C++ exceptions 
>> (AFAIK it's following C specs, not C++), so C++ exceptions 
>> should not even be a consideration at that point. I do not 
>> think that throwing a C++ exception up a stack that contains 
>> extern(C) functions is even properly defined behavior on the 
>> C++ side. In other words, all ImportC declarations should be 
>> implicitly @nothrow.
>
> Its defined for MSVC:
>
> https://learn.microsoft.com/en-us/cpp/cpp/structured-exception-handling-c-cpp?view=msvc-170
>
> "Structured exception handling (SEH) is a Microsoft extension 
> to C and C++ to handle certain exceptional code situations, 
> such as hardware faults, gracefully."
>
> I'm pretty sure for other platforms it is also defined as part 
> of unwinding, although I can't be bothered to hunt for the 
> specification. It's not about C, it's about languages that are 
> not C++ (consider JIT's for instance).

That is a special case, given how C++ is relevant in the 
Microsoft ecosystem, and SEH existence, you won't find that in 
other platforms, not even on UNIX where C++ was born alongside C.

I am not even sure that is even covered on Itanium ABI that most 
modern compilers have meanwhile adopted on remaining UNIX 
platforms.