https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91222
Jason Merrill <jason at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |jason at gcc dot gnu.org
--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Jan Hubicka from comment #2)
> 2.ii:62:3: warning: ‘ml_bssnrest_’ violates the C++ One Definition Rule
> [-Wodr]
> 62 | } ml_bssnrest_;
> | ^
> 1.ii:2:8: note: type ‘struct <anon>’ defined in anonymous namespace cannot
> match across the translation unit boundary
> 2 | struct {
> | ^
> 2.ii:2:15: note: the incompatible type defined in another translation unit
> 2 | extern struct {
> | ^
> 1.ii:62:3: note: ‘ml_bssnrest_’ was previously declared here
> 62 | } ml_bssnrest_;
> | ^
>
> Now I wonder why C++ FE makes the struct anonymous namespace when it is
> declared with extern "C".
> I have checked that type_in_anonymous_namespace_p(prevailing_type) returns
> true because mangled name is <anon> which comes from C++ FE.
>
> I will check in the patch to avoid ICE. Jason, can you please look if it is
> correct to consider these types anonymous?
They aren't in the anonymous namespace, but they are themselves anonymous, so
they have no linkage. The standard says,
A type without linkage shall not be used as the type of a variable or function
with external linkage unless
— the entity has C language linkage (7.5), or
— the entity is declared within an unnamed namespace (7.3.1), or
— the entity is not odr-used (3.2) or is defined in the same translation unit.
Here 1.ii is OK under the third bullet, and 2.ii under the first bullet.
Within extern "C" I guess we need to do structural comparison for anonymous
types rather than rely on the ODR.
