Close https://github.com/llvm/llvm-project/issues/60890.
For the following example:
export module a;
export template<typename T>
struct a {
friend void aa(a) requires(true) {
}
};export module b;
import a;
struct b {
a<int> m;
};export module c;
import a;
struct c {
void f() const {
aa(a<int>());
}
};import a;
import b;
import c;
void d() {
aa(a<int>());
}The current clang will reject this incorrectly. The reason is that the require clause will be replaced with the evaluated version (https://github.com/llvm/llvm-project/blob/efae3174f09560353fb0f3d528bcbffe060d5438/clang/lib/Sema/SemaConcept.cpp#L664-L665). In module 'b', the friend function is instantiated but not used so the require clause of the friend function is (true). However, in module 'c', the friend function is used so the require clause is true. So deserializer classify these two function to two different functions instead of one. Then here is the bug report.
The proposed solution is to try to compare the trailing require clause of the primary template when performing ODR checking.