[PATCH] c++: P0848R3 and member function templates [PR95181]

[Patrick Palka]

When comparing two special member function templates to see if one hides
the other (as per P0848R3), we need to check satisfaction which we can't
do on templates.  So this patch makes add_method skip the eligibility
test on member function templates and just lets them coexist.

Passes 'make check-c++', does this look OK to commit to master and later
to the 10 branch?

gcc/cp/ChangeLog:

	PR c++/95181
	* class.c (add_method): Let special member function templates
	coexist if they are not equivalently constrained.

gcc/testsuite/ChangeLog:

	PR c++/95181
	* g++.dg/concepts/pr95181.C: New test.
---
 gcc/cp/class.c                          | 10 ++++++----
 gcc/testsuite/g++.dg/concepts/pr95181.C |  9 +++++++++
 2 files changed, 15 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/concepts/pr95181.C

diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index bab15524a60..cb268d191d6 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -1079,10 +1079,12 @@ add_method (tree type, tree method, bool via_using)
 	    {
 	      special_function_kind sfk = special_memfn_p (method);
 
-	      if (sfk == sfk_none || DECL_INHERITED_CTOR (fn))
-		/* Non-special member functions coexist if they are not
-		   equivalently constrained.  A member function is not hidden
-		   by an inherited constructor.  */
+	      if (sfk == sfk_none
+		  || DECL_INHERITED_CTOR (fn)
+		  || TREE_CODE (fn) == TEMPLATE_DECL)
+		/* Member function templates and non-special member functions
+		   coexist if they are not equivalently constrained.  A member
+		   function is not hidden by an inherited constructor.  */
 		continue;
 
 	      /* P0848: For special member functions, deleted, unsatisfied, or
diff --git a/gcc/testsuite/g++.dg/concepts/pr95181.C b/gcc/testsuite/g++.dg/concepts/pr95181.C
new file mode 100644
index 00000000000..0185c86b438
--- /dev/null
+++ b/gcc/testsuite/g++.dg/concepts/pr95181.C
@@ -0,0 +1,9 @@
+// PR c++/95181
+// { dg-do compile { target concepts } }
+
+template <typename> struct f {
+  template <typename T=int> f();
+  template <typename T=int> requires false f();
+};
+
+f<int> a;
-- 
2.27.0.rc1.5.gae92ac8ae3