member_like_constrained_friend_p was incorrectly returning true for
constrained friend function templates declared in non-template classes,
causing them to be treated as distinct from their forward declarations.
This led to ambiguity errors at call sites.
Per [temp.friend]/9, a constrained friend is only "member-like" (and thus
declares a different function) in two cases:
1. Non-template friends with constraints (must be in a templated class)
2. Template friends whose constraints depend on outer template parameters
In both cases, the enclosing class scope must be templated. The fix adds
a check for CLASSTYPE_IMPLICIT_INSTANTIATION to ensure the friend's
context is actually a class template, not a plain class or explicit
specialization.
PR c++/122550
gcc/cp/ChangeLog:
* decl.cc (member_like_constrained_friend_p): Check that the
friend's enclosing class is an implicit instantiation.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-friend18.C: New test.
* g++.dg/cpp2a/concepts-friend18a.C: New test.
Signed-off-by: Egas Ribeiro <[email protected]>
---
gcc/cp/decl.cc | 1 +
.../g++.dg/cpp2a/concepts-friend18.C | 19 ++++++++++++++++
.../g++.dg/cpp2a/concepts-friend18a.C | 22 +++++++++++++++++++
3 files changed, 42 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-friend18.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-friend18a.C
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 30f38f1e099..f41b3fc0471 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -1129,6 +1129,7 @@ member_like_constrained_friend_p (tree decl)
&& DECL_UNIQUE_FRIEND_P (decl)
&& DECL_FRIEND_CONTEXT (decl)
&& get_constraints (decl)
+ && CLASSTYPE_IMPLICIT_INSTANTIATION (DECL_FRIEND_CONTEXT (decl))
&& (!DECL_TEMPLATE_INFO (decl)
|| !PRIMARY_TEMPLATE_P (DECL_TI_TEMPLATE (decl))
|| (uses_outer_template_parms_in_constraints
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-friend18.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-friend18.C
new file mode 100644
index 00000000000..bd1bac6cdac
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-friend18.C
@@ -0,0 +1,19 @@
+// PR c++/122550
+// { dg-do compile { target c++20 } }
+
+struct Hasher;
+template <class a>
+concept C = true;
+
+template<C T>
+void add(Hasher&, T);
+
+struct Hasher {
+ template<C T>
+ friend void add(Hasher& hasher, T integer) {}
+};
+
+int main() {
+ Hasher h;
+ add(h, 0);
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-friend18a.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-friend18a.C
new file mode 100644
index 00000000000..d29a2fba037
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-friend18a.C
@@ -0,0 +1,22 @@
+// PR c++/122550
+// { dg-do compile { target c++20 } }
+
+template<typename U>
+struct Hasher;
+
+template <class a>
+concept C = true;
+
+template<C T>
+void add(Hasher<int>&, T);
+
+template<>
+struct Hasher<int> {
+ template<C T>
+ friend void add(Hasher& hasher, T integer) {}
+};
+
+int main() {
+ Hasher<int> h;
+ add(h, 0);
+}
--
2.52.0
