From 6d082cd90131a9c0ce3142217e84194a5bf0de27 Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Thu, 5 Mar 2020 10:04:06 -0500 Subject: [PATCH] libstdc++: Give ranges::empty() a concrete return type (PR 93978) This works around PR 93978 by avoiding having to instantiate the body of ranges::empty() when checking the constraints of view_interface::operator bool(). When ranges::empty() has an auto return type, then we must instantiate its body in order to determine whether the requires expression { ranges::empty(_M_derived()); } is well-formed. But this means instantiating view_interface::empty() and hence view_interface::_M_derived(), all before we've yet deduced the return type of join_view::end(). (The reason view_interface::operator bool() is needed in join_view::end() in the first place is because in this function we perform direct initialization of join_view::_Sentinel from a join_view, and so we try to find a conversion sequence from the latter to the former that goes through this conversion operator.) Giving ranges::empty() a concrete return type of bool should be safe according to [range.prim.empty]/4 which says "whenever ranges::empty(E) is a valid expression, it has type bool." This fixes the test case in PR 93978 when compiling without -Wall, but with -Wall the test case still fails due to the issue described in PR c++/94038, I think. I still don't quite understand why the test case doesn't fail without -O. libstdc++-v3/ChangeLog: PR libstdc++/93978 * include/bits/range_access.h (__cust_access::_Empty::operator()): Declare return type to be bool instead of auto. * testsuite/std/ranges/adaptors/93978.cc: New test. --- libstdc++-v3/ChangeLog | 7 ++++ libstdc++-v3/include/bits/range_access.h | 2 +- .../testsuite/std/ranges/adaptors/93978.cc | 35 +++++++++++++++++++ 3 files changed, 43 insertions(+), 1 deletion(-) create mode 100644 libstdc++-v3/testsuite/std/ranges/adaptors/93978.cc diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index 98faff614da..b2e995b4daf 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,3 +1,10 @@ +2020-03-06 Patrick Palka + + PR libstdc++/93978 + * include/bits/range_access.h (__cust_access::_Empty::operator()): + Declare return type to be bool instead of auto. + * testsuite/std/ranges/adaptors/93978.cc: New test. + 2020-03-06 Jonathan Wakely PR libstdc++/94069 diff --git a/libstdc++-v3/include/bits/range_access.h b/libstdc++-v3/include/bits/range_access.h index 8b276fd6625..4dd48bbc6df 100644 --- a/libstdc++-v3/include/bits/range_access.h +++ b/libstdc++-v3/include/bits/range_access.h @@ -793,7 +793,7 @@ namespace ranges template requires __member_empty<_Tp> || __size0_empty<_Tp> || __eq_iter_empty<_Tp> - constexpr auto + constexpr bool operator()(_Tp&& __e) const noexcept(_S_noexcept<_Tp>()) { if constexpr (__member_empty<_Tp>) diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/93978.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/93978.cc new file mode 100644 index 00000000000..a0152ec0532 --- /dev/null +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/93978.cc @@ -0,0 +1,35 @@ +// Copyright (C) 2020 Free Software Foundation, Inc. +// +// This file is part of the GNU ISO C++ Library. This library is free +// software; you can redistribute it and/or modify it under the +// terms of the GNU General Public License as published by the +// Free Software Foundation; either version 3, or (at your option) +// any later version. + +// This library is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. + +// You should have received a copy of the GNU General Public License along +// with this library; see the file COPYING3. If not see +// . + +// { dg-options "-std=gnu++2a" } +// { dg-additional-options "-O" } +// { dg-do compile { target c++2a } } + +#include +#include + +namespace ranges = std::ranges; +namespace views = std::views; + +void +test() +{ + std::vector x = {""}; + auto i = std::counted_iterator(x.begin(), 1); + auto r = ranges::subrange{i, std::default_sentinel}; + auto v = r | views::join; +} -- 2.30.2