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From: "mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/109680] [13/14 Regression] is_convertible<int() const,
 int(*)()> incorrectly true
Date: Mon, 01 May 2023 23:13:14 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109680

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #4)
> template <typename T, typename U =3D T&&>
> U __declval (int);
> template <typename T>
> T __declval (long);
> template <typename T>
> auto declval () noexcept -> decltype (__declval <T> (0));
> using To =3D int () const;
> using From =3D int (*) ();
> To foo () { return declval <From> (); }
> From bar () { return declval <To> (); }
> static_assert (!__is_convertible (To, From), "");
> static_assert (!__is_convertible (From, To), "");
> should show that both assertions should succeed.=20=20

Thanks.

> Dunno if in this case the
> reason why it isn't convertible is simply the fact that functions can't be
> declared to return function/method/array types or some other reason as we=
ll.

Yeah, I'm also not sure, so I think this should fix it:

--- a/gcc/cp/method.cc
+++ b/gcc/cp/method.cc
@@ -2245,6 +2245,8 @@ is_convertible_helper (tree from, tree to)
 {
   if (VOID_TYPE_P (from) && VOID_TYPE_P (to))
     return integer_one_node;
+  if (FUNC_OR_METHOD_TYPE_P (from) || FUNC_OR_METHOD_TYPE_P (to))
+    return error_mark_node;
   cp_unevaluated u;
   tree expr =3D build_stub_object (from);
   deferring_access_check_sentinel acs (dk_no_deferred);


Since
static_assert (!__is_convertible (int[3], int[3]), "");
already passes, arrays are handled correctly I think.=