<xutility>: `ranges::_Ssize_fn::operator()` should have a noexcept-specifier

[cpplearner]

Describe the bug

ranges::ssize(a) is specified to be expression-equivalent to static_cast<D>(ranges::size(a)) (for some integer-like type D), which means applying noexcept to these two expressions should produce the same result. But due to a missing noexcept-specifier, noexcept(ranges::ssize(a)) is always false on MSVC, which is non-conforming.

This can be fixed by adding a conditional noexcept-specifier to ranges::_Ssize_fn::operator(). Since D is integer-like, the cast should never throw an exception, so the noexcept-specifier only needs to mention the ranges::size call.

I think this could be a "good first issue".

Command-line test case

D:\test>type test-ssize.cpp
#include <ranges>

int a[10];
static_assert(noexcept(std::ranges::ssize(a)));

D:\test>cl /Zs /std:c++20 test-ssize.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 19.38.33030 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

test-ssize.cpp
test-ssize.cpp(4): error C2607: static assertion failed

Expected behavior

no error

STL version

Microsoft Visual Studio Community 2022
Version 17.8.0 Preview 2.0

[frederick-vs-ja]

Suggestions

(for the "good first issue" case)

Product code

STL/stl/inc/xutility

Line 3393 in 1c59a20

_NODISCARD constexpr auto operator()(_Rng&& _Range) const requires requires { _RANGES size(_Range); } {

Add the noexcept-specifier here. The operator() should be non-throwing if and only if _RANGES size(_Range) is non-throwing. (Clang-format may be needed.)

Test code

STL/tests/std/tests/P0896R4_ranges_range_machinery/test.cpp

Line 1493 in 1c59a20

STATIC_ASSERT(noexcept(ranges::size(t)) == Nothrow);

Add test coverage for ranges::ssize after that for ranges::size. Again, they should be both potentially throwing or both non-throwing.