https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119939
Bug ID: 119939
Summary: [modules] Constraints attached to defaulted friend
functions don't work correctly
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: nshead at gcc dot gnu.org
Blocks: 103524
Target Milestone: ---
Consider the following:
// test.h
template <typename T> concept A = true;
template <typename T> concept B = requires { T{}; };
template <typename T> struct S {
friend bool operator==(const S&, const S&) requires B<T> = default;
};
// test.cpp
import "test.h";
int main() {
S<int> s;
s == s;
}
$ g++ -std=c++20 -fmodules -S test.h test.cpp -fconcepts-diagnostics-depth=2
test.cpp: In function ‘int main()’:
test.cpp:5:5: error: no match for ‘operator==’ (operand types are ‘S<int>’ and
‘S<int>’)
5 | s == s;
| ~ ^~ ~
| | |
| | S<[...]>
| S<[...]>
test.cpp:5:5: note: there is 1 candidate
5 | s == s;
| ~~^~~~
In module test.h, imported at test.cpp:1:
test.h:4:15: note: candidate 1: ‘bool operator==(const S<int>&, const S<int>&)
requires B<T>’
4 | friend bool operator==(const S&, const S&) requires B<T> = default;
| ^~~~~~~~
test.h:4:15: note: constraints not satisfied
test.h: In instantiation of ‘bool operator==(const S<int>&, const S<int>&)
requires B<T>’:
test.cpp:5:8: required from here
5 | s == s;
| ^
test.h:2:31: required for the satisfaction of ‘B<T>’
test.h:2:35: in requirements [with T = T]
test.h:2:46: note: the required expression ‘T{}’ is invalid, because
2 | template <typename T> concept B = requires { T{}; };
| ^~~
test.h:2:46: error: invalid use of template type parameter ‘T’
This is because by the time we get to satisfy_declaration_constraints in the
importing module, the friend function no longer has template arguments attached
to it, and so constraint satisfaction gets confused. When not importing the
DECL_TEMPLATE_INFO is still attached to this declaration; it seems that module
streaming should still stream this info even if the decl isn't strictly a
template anymore.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103524
[Bug 103524] [meta-bug] modules issue
