From c45f382a12fc8ccc7324baad121ba5d262aab214 Mon Sep 17 00:00:00 2001
From: Igor Zhukov <fsb4000@yandex.ru>
Date: Tue, 13 Dec 2022 07:07:26 +0700
Subject: [PATCH] Implement LWG-3646 std::ranges::view_interface::size returns
 a signed type

Reviewed By: Mordante, philnik, #libc

Differential Revision: https://reviews.llvm.org/D139791
---
 libcxx/docs/Status/Cxx2bIssues.csv                                  | 2 ++
 libcxx/include/__ranges/view_interface.h                            | 4 ++--
 .../std/ranges/range.utility/view.interface/view.interface.pass.cpp | 6 ++++++
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/libcxx/docs/Status/Cxx2bIssues.csv b/libcxx/docs/Status/Cxx2bIssues.csv
index 756c686..c648938 100644
--- a/libcxx/docs/Status/Cxx2bIssues.csv
+++ b/libcxx/docs/Status/Cxx2bIssues.csv
@@ -186,6 +186,8 @@
 "`3721 <https://wg21.link/LWG3721>`__","Allow an ``arg-id`` with a value of zero for ``width`` in ``std-format-spec``","July 2022","|Complete|","16.0","|format|"
 "`3724 <https://wg21.link/LWG3724>`__","``decay-copy`` should be constrained","July 2022","|Complete|","14.0"
 "","","","",""
+"`3646 <https://wg21.link/LWG3646>`__","``std::ranges::view_interface::size`` returns a signed type","November 2022","|Complete|","16.0"
+"","","","",""
 "`3629 <https://wg21.link/LWG3629>`__","``make_error_code`` and ``make_error_condition`` are customization points","Not voted in","|Complete|","16.0",""
 "`3631 <https://wg21.link/LWG3631>`__","``basic_format_arg(T&&)`` should use ``remove_cvref_t<T>`` throughout","Not voted in","|Complete|","15.0",""
 "`3645 <https://wg21.link/LWG3645>`__","``resize_and_overwrite`` is overspecified to call its callback with lvalues","Not voted in","|Complete|","14.0",""
diff --git a/libcxx/include/__ranges/view_interface.h b/libcxx/include/__ranges/view_interface.h
index b89ee99..b706c8d 100644
--- a/libcxx/include/__ranges/view_interface.h
+++ b/libcxx/include/__ranges/view_interface.h
@@ -100,7 +100,7 @@ public:
   constexpr auto size()
     requires forward_range<_D2> && sized_sentinel_for<sentinel_t<_D2>, iterator_t<_D2>>
   {
-    return ranges::end(__derived()) - ranges::begin(__derived());
+    return std::__to_unsigned_like(ranges::end(__derived()) - ranges::begin(__derived()));
   }
 
   template<class _D2 = _Derived>
@@ -108,7 +108,7 @@ public:
   constexpr auto size() const
     requires forward_range<const _D2> && sized_sentinel_for<sentinel_t<const _D2>, iterator_t<const _D2>>
   {
-    return ranges::end(__derived()) - ranges::begin(__derived());
+    return std::__to_unsigned_like(ranges::end(__derived()) - ranges::begin(__derived()));
   }
 
   template<class _D2 = _Derived>
diff --git a/libcxx/test/std/ranges/range.utility/view.interface/view.interface.pass.cpp b/libcxx/test/std/ranges/range.utility/view.interface/view.interface.pass.cpp
index 2c1c504..830f3f7 100644
--- a/libcxx/test/std/ranges/range.utility/view.interface/view.interface.pass.cpp
+++ b/libcxx/test/std/ranges/range.utility/view.interface/view.interface.pass.cpp
@@ -233,12 +233,18 @@ constexpr bool testSize() {
   static_assert(!SizeInvocable<NotSizedSentinel>);
   static_assert( SizeInvocable<ForwardRange>);
 
+  using SignedSize = std::common_type_t<std::ptrdiff_t, std::make_signed_t<std::size_t>>;
   ForwardRange forwardRange;
   assert(forwardRange.size() == 8);
   assert(static_cast<ForwardRange const&>(forwardRange).size() == 8);
 
   assert(std::ranges::size(forwardRange) == 8);
+  static_assert(std::same_as<decltype(std::ranges::size(std::declval<ForwardRange>())), std::size_t>);
+  static_assert(std::same_as<decltype(std::ranges::ssize(std::declval<ForwardRange>())), SignedSize>);
+
   assert(std::ranges::size(static_cast<ForwardRange const&>(forwardRange)) == 8);
+  static_assert(std::same_as<decltype(std::ranges::size(std::declval<ForwardRange const>())), std::size_t>);
+  static_assert(std::same_as<decltype(std::ranges::ssize(std::declval<ForwardRange const>())), SignedSize>);
 
   SizeIsTen sizeTen;
   assert(sizeTen.size() == 10);
-- 
2.7.4