https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119983
--- Comment #4 from gap mman <g.mjardev at gmail dot com> ---
(In reply to Nathaniel Shead from comment #2)
> Thanks for the report! As Andrew noted, the ICE is fixed for 14.3 by
> r14-10825-g01d3a974fe3474c37cd52b595c29dddafad954dc.
>
> The code is ill-formed, however:
>
> export module M;
> struct {} instance;
>
> is not legal in a module interface, because of
> https://eel.is/c++draft/basic.link#15.2 (the type of the unnamed struct is
> TU-local), https://eel.is/c++draft/basic.link#14 (the declaration of the
> variable exposes the TU-local type), and
> https://eel.is/c++draft/basic.link#17 (the variable is not TU-local, so this
> is ill-formed).
>
> We don't check this in GCC 14 (so 14.3 will accept this code), but for GCC
> 15 we properly implement https://wg21.link/p1815 and so error in this case:
>
> <source>:2:11: error: 'instance' exposes TU-local entity 'struct<unnamed>'
> 2 | struct {} instance;
> | ^~~~~~~~
> <source>:2:8: note: '<unnamed struct>' has no name and is not defined within
> a class, function, or initializer
> 2 | struct {} instance;
> | ^
Thank you for answering. I'm only using this variable within the TU.
Am I correct in understanding the problem as the following: The instance, even
though not visible outside of the module, doesn't have internal linkage but
names a TU local entity (the unnamed type), which causes exposure and is
therefore ill formed. To fix, either name the type to make it not TU local or
make the variable have internal linkage (adding `static` as in the example).
As for a fix in current GCC14.2 I'm using, my only bet is naming this type? I'm
actually declaring it `constexpr`(which, unfortunately, is explicitly defined
as exposure)
```
constexpr struct
{
void aRandomFunc()
{
}
} variableWithNamelessType{};
```
I also noticed something I didn't quite understand in GCC14.2. If I declare
this as `static constexpr` and use it in an exported function, then I'm fine;
but if the function is templatized, then I get "references internal linkage
entity". https://godbolt.org/z/3rKn3v7rq In GCC 15 both works, which I believe
should be the correct behavior?
