https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119844
Nathaniel Shead <nshead at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |diagnostic
CC| |nshead at gcc dot gnu.org
--- Comment #2 from Nathaniel Shead <nshead at gcc dot gnu.org> ---
I haven't attempted to fully reproduce, but it appears to me you have something
like the following:
// user.cpp
export module User;
export struct User {
int value;
};
// main.cpp
struct User;
struct MainWindow {
User* u;
};
import User;
int foo(MainWindow m) {
return m.u->value;
}
$ g++-15 -fmodules -S user.cpp main.cpp
main.cpp: In function ‘int foo(MainWindow)’:
main.cpp:7:13: error: invalid use of incomplete type ‘struct User’
7 | return m.u->value;
| ^~
main.cpp:1:8: note: forward declaration of ‘struct User’
1 | struct User;
| ^~~~
This error is expected (though the diagnostic could definitely be improved!):
'User' (in main.cpp) and 'User@User' (in user.cpp) are unrelated, distinct
types; the former belonging to the global module, and the latter attached to
the module 'User'. You can see this by comparing e.g.:
// main.cpp
struct User;
import User;
User u;
$ g++-15 -fmodules -S user.cpp main.cpp
main.cpp:3:1: error: reference to ‘User’ is ambiguous
3 | User u;
| ^~~~
In module User, imported at main.cpp:2:
user.cpp:2:15: note: candidates are: ‘struct User@User’
2 | export struct User {
| ^~~~
main.cpp:1:8: note: ‘struct User’
1 | struct User;
| ^~~~
To fix the issue, you could defined user.cpp as something like this:
// user.cpp
export module User;
export extern "C++" struct User {
int value;
};
The 'extern "C++"' ensures that 'User' is declared attached to the global
module.
I'll leave this PR open for now for the diagnostic issue, however, as I imagine
this to be a common mistake, and we should be able to detect this and emit some
kind of note pointing to the conflicting type.
