[gcc/devel/ranger] c++: Fix invalid pointer-to-member in requires [PR67825]

[Aldy Hernandez]

https://gcc.gnu.org/g:f1ad7bac76b662577e3bde78c530954099361a66

commit f1ad7bac76b662577e3bde78c530954099361a66
Author: Jason Merrill <jason@redhat.com>
Date:   Sat Apr 4 11:04:55 2020 -0400

    c++: Fix invalid pointer-to-member in requires [PR67825]
    
    A recent change to cmcstl2 led to two tests failing due to this bug: our
    valid expression checking in the context of a requires-expression wasn't
    catching that an expression of member function type can only appear as the
    function operand of a call expression.  Fixed by using convert_to_void to do
    the same checking as a discarded-value expression.
    
    This patch also fixes 67825, which already had a testcase, but the testcase
    was testing for the wrong behavior.
    
    gcc/cp/ChangeLog
    2020-04-04  Jason Merrill  <jason@redhat.com>
    
            PR c++/67825
            * constraint.cc (tsubst_valid_expression_requirement): Call
            convert_to_void.

Diff:
---
 gcc/cp/ChangeLog                              |  6 ++++++
 gcc/cp/constraint.cc                          |  5 ++++-
 gcc/testsuite/g++.dg/cpp2a/concepts-pmf1.C    | 22 ++++++++++++++++++++++
 gcc/testsuite/g++.dg/cpp2a/concepts-pr67825.C |  2 +-
 4 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index f8229368eb9..860d5d36cf6 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2020-04-04  Jason Merrill  <jason@redhat.com>
+
+	PR c++/67825
+	* constraint.cc (tsubst_valid_expression_requirement): Call
+	convert_to_void.
+
 2020-04-04  Jason Merrill  <jason@redhat.com>
 
 	PR c++/94453
diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 9c21ce80256..e5308414879 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -1864,7 +1864,10 @@ hash_placeholder_constraint (tree c)
 static tree
 tsubst_valid_expression_requirement (tree t, tree args, subst_info info)
 {
-  return tsubst_expr (t, args, info.complain, info.in_decl, false);
+  tree r = tsubst_expr (t, args, info.complain, info.in_decl, false);
+  if (convert_to_void (r, ICV_STATEMENT, info.complain) == error_mark_node)
+    return error_mark_node;
+  return r;
 }
 
 
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-pmf1.C b/gcc/testsuite/g++.dg/cpp2a/concepts-pmf1.C
new file mode 100644
index 00000000000..30d2b2d4a48
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-pmf1.C
@@ -0,0 +1,22 @@
+// Make sure that the requirement fails because a .* expression of function
+// type can only be used in a call.
+
+// { dg-do compile { target concepts } }
+
+template<class D, class T>
+constexpr decltype(auto) invoke(D (T::*pmd), T&& t)
+  noexcept(noexcept(t.*pmd))
+  requires requires { t.*pmd; }
+ { return t.*pmd; }
+
+char invoke(...);
+
+struct A
+{
+  int f();
+};
+
+int main()
+{
+  static_assert(sizeof(invoke (&A::f, A())) == 1);
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-pr67825.C b/gcc/testsuite/g++.dg/cpp2a/concepts-pr67825.C
index 95698e99978..fff414b8eb2 100644
--- a/gcc/testsuite/g++.dg/cpp2a/concepts-pr67825.C
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-pr67825.C
@@ -15,6 +15,6 @@ template <class X> concept bool C() {
 }
 
 int main() {
-  static_assert(C<A>());
+  static_assert(!C<A>());
   return 0;
 }