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[libc++] Verify std::forward_like's mandates clause. (#127318)

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The existing using _ForwardLike declaration already fails with a
subsitution failure. The LWG issue was filed to clarify what should
happen for non-referencable types.

Added test to verify libc++ is already enforcing the new Mandates.

Implements:
- LWG3757 What's the effect of std::forward_like<void>(x)

Closes: #105026
This commit is contained in:
Mark de Wever
2025-03-27 01:53:30 +01:00
committed by GitHub
parent a629b50575
commit f9aa7a20d9
2 changed files with 47 additions and 1 deletions
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2
libcxx/docs/Status/Cxx23Issues.csv
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@@ -213,7 +213,7 @@
"`LWG3753 <https://wg21.link/LWG3753>`__","Clarify entity vs. freestanding entity","2022-11 (Kona)","","",""
"`LWG3754 <https://wg21.link/LWG3754>`__","Class template expected synopsis contains declarations that do not match the detailed description","2022-11 (Kona)","|Nothing To Do|","",""
"`LWG3755 <https://wg21.link/LWG3755>`__","``tuple-for-each`` can call ``user-defined`` ``operator,``","2022-11 (Kona)","|Complete|","17",""
"`LWG3757 <https://wg21.link/LWG3757>`__","What's the effect of ``std::forward_like<void>(x)``?","2022-11 (Kona)","","",""
"`LWG3757 <https://wg21.link/LWG3757>`__","What's the effect of ``std::forward_like<void>(x)``?","2022-11 (Kona)","|Nothing To Do|","",""
"`LWG3759 <https://wg21.link/LWG3759>`__","``ranges::rotate_copy`` should use ``std::move``","2022-11 (Kona)","|Complete|","15",""
"`LWG3760 <https://wg21.link/LWG3760>`__","``cartesian_product_view::iterator``'s ``parent_`` is never valid","2022-11 (Kona)","","",""
"`LWG3761 <https://wg21.link/LWG3761>`__","``cartesian_product_view::iterator::operator-`` should pass by reference","2022-11 (Kona)","","",""
1 Issue # Issue Name Meeting Status First released version Notes
213 `LWG3753 <https://wg21.link/LWG3753>`__ Clarify entity vs. freestanding entity 2022-11 (Kona)
214 `LWG3754 <https://wg21.link/LWG3754>`__ Class template expected synopsis contains declarations that do not match the detailed description 2022-11 (Kona) |Nothing To Do|
215 `LWG3755 <https://wg21.link/LWG3755>`__ ``tuple-for-each`` can call ``user-defined`` ``operator,`` 2022-11 (Kona) |Complete| 17
216 `LWG3757 <https://wg21.link/LWG3757>`__ What's the effect of ``std::forward_like<void>(x)``? 2022-11 (Kona) |Nothing To Do|
217 `LWG3759 <https://wg21.link/LWG3759>`__ ``ranges::rotate_copy`` should use ``std::move`` 2022-11 (Kona) |Complete| 15
218 `LWG3760 <https://wg21.link/LWG3760>`__ ``cartesian_product_view::iterator``'s ``parent_`` is never valid 2022-11 (Kona)
219 `LWG3761 <https://wg21.link/LWG3761>`__ ``cartesian_product_view::iterator::operator-`` should pass by reference 2022-11 (Kona)

46
libcxx/test/std/utilities/utility/forward/forward_like.verify.cpp Normal file
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@@ -0,0 +1,46 @@
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// REQUIRES: std-at-least-c++23
// <utility>
// template <typename T>
// [[nodiscard]] constexpr
// auto forward_like(auto&& x) noexcept -> see below;
// Mandates: T is a referenceable type (3.45 [defns.referenceable]).
#include <utility>
struct incomplete;
void test() {
int i;
(void)std::forward_like<incomplete>(i);
(void)std::forward_like<void>(i); // expected-error {{no matching function for call to 'forward_like'}}
(void)std::forward_like<const void>(i); // expected-error {{no matching function for call to 'forward_like'}}
(void)std::forward_like<volatile void>(i); // expected-error {{no matching function for call to 'forward_like'}}
(void)std::forward_like<const volatile void>(i); // expected-error {{no matching function for call to 'forward_like'}}
using fp = void();
using cfp = void() const;
using vfp = void() volatile;
using cvfp = void() const volatile;
(void)std::forward_like<fp>(i);
(void)std::forward_like<cfp>(i); // expected-error {{no matching function for call to 'forward_like'}}
(void)std::forward_like<cfp>(i); // expected-error {{no matching function for call to 'forward_like'}}
(void)std::forward_like<vfp>(i); // expected-error {{no matching function for call to 'forward_like'}}
(void)std::forward_like<cvfp>(i); // expected-error {{no matching function for call to 'forward_like'}}
using fpr = void()&;
using fprr = void()&&;
(void)std::forward_like<fpr>(i); // expected-error {{no matching function for call to 'forward_like'}}
(void)std::forward_like<fprr>(i); // expected-error {{no matching function for call to 'forward_like'}}
}