[clang++] Implicit template instantiations in modules cause errors in other modules #125521
Description
If module A instantiates a template Class<T>, any module that imports module A and also tries to instantiate Class<T> (with the same T) will get an error:
/home/modBug/reproducer/src/hello.h:8:38: error: declaration 'get' attached to named module 'Mod2' can't be attached to other modules
8 | template <typename V> friend int get() noexcept;
| ^
/home/modBug/reproducer/src/hello.h:3:27: note: also found
3 | template <typename V> int get() noexcept {return 0;};
| ^
See this reproducer or https://godbolt.org/z/d7YW7TM4a where instantiating List<int> in Mod2 causes any module that also imports Mod2 to fail to instantiate List<int>.
I think this is a bug because the global module fragment is not supposed to be exported.
Reproducer:
hello.h:
template <typename V> int get() noexcept {return 0;};
template <typename T>
class List
{
template <typename V> friend int get() noexcept;
};
mod.cpp:
module;
#include "hello.h"
export module Mod;
import Mod2;
export const char *modFn() {
List<int> a;
List<double> b;
return modFn2();
}
mod2.cpp:
module;
#include "hello.h"
export module Mod2;
export const char *modFn2() {
List<int> a;
return "hello";
}
main.cpp:
#include <iostream>
import Mod;
int main(int argc, char** argv) {
std::cout << modFn() << '\n';
}
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