[libcxx-commits] [libcxx] 8e92410 - [libc++][docs] Mark LWG3274 as complete

[Joe Loser via libcxx-commits]

Author: Joe Loser
Date: 2021-10-12T22:31:32-04:00
New Revision: 8e92410ecc86f3ad29e038bf1abad7aa3fc20e7b

URL: https://github.com/llvm/llvm-project/commit/8e92410ecc86f3ad29e038bf1abad7aa3fc20e7b
DIFF: https://github.com/llvm/llvm-project/commit/8e92410ecc86f3ad29e038bf1abad7aa3fc20e7b.diff

LOG: [libc++][docs] Mark LWG3274 as complete

Mark LWG3274 as complete. The feature test macro `__cpp_lib_span` was added in
`6d2599e4f776d0cd88438cb82a00c4fc25cc3f67`.

https://wg21.link/p1024 mentions marking `span:::empty()` with
`[[nodiscard]]` which is not done yet. So, do that and add tests.

Reviewed By: ldionne, Quuxplusone, Mordante, #libc

Differential Revision: https://reviews.llvm.org/D111516

Added: 
    libcxx/test/std/containers/views/span.obs/empty.nodiscard.verify.cpp

Modified: 
    libcxx/docs/Status/Cxx20Issues.csv
    libcxx/include/span
    libcxx/test/std/containers/views/span.obs/empty.pass.cpp

Removed: 
    


################################################################################
diff  --git a/libcxx/docs/Status/Cxx20Issues.csv b/libcxx/docs/Status/Cxx20Issues.csv
index f835afdf268e..6b286203afc3 100644
--- a/libcxx/docs/Status/Cxx20Issues.csv
+++ b/libcxx/docs/Status/Cxx20Issues.csv
@@ -183,7 +183,7 @@
 "`3272 <https://wg21.link/LWG3272>`__","``%I%p``\  should parse/format ``duration``\  since midnight","Belfast","",""
 "`3259 <https://wg21.link/LWG3259>`__","The definition of *constexpr iterators* should be adjusted","Belfast","",""
 "`3103 <https://wg21.link/LWG3103>`__","Errors in taking subview of ``span``\  should be ill-formed where possible","Belfast","",""
-"`3274 <https://wg21.link/LWG3274>`__","Missing feature test macro for ``<span>``\ ","Belfast","",""
+"`3274 <https://wg21.link/LWG3274>`__","Missing feature test macro for ``<span>``\ ","Belfast","|Complete|","11.0"
 "`3276 <https://wg21.link/LWG3276>`__","Class ``split_view::outer_iterator::value_type``\  should inherit from ``view_interface``\ ","Belfast","",""
 "`3277 <https://wg21.link/LWG3277>`__","Pre-increment on prvalues is not a requirement of ``weakly_incrementable``\ ","Belfast","",""
 "`3149 <https://wg21.link/LWG3149>`__","``DefaultConstructible``\  should require default initialization","Belfast","|Complete|","13.0"

diff  --git a/libcxx/include/span b/libcxx/include/span
index 2f1a19d42bcd..29f833f6022d 100644
--- a/libcxx/include/span
+++ b/libcxx/include/span
@@ -89,7 +89,7 @@ public:
     // [span.obs], span observers
     constexpr size_type size() const noexcept;
     constexpr size_type size_bytes() const noexcept;
-    constexpr bool empty() const noexcept;
+    [[nodiscard]] constexpr bool empty() const noexcept;
 
     // [span.elem], span element access
     constexpr reference operator[](size_type idx) const;
@@ -330,9 +330,9 @@ public:
         return {data() + __offset, __count};
     }
 
-    _LIBCPP_INLINE_VISIBILITY constexpr size_type size()       const noexcept { return _Extent; }
-    _LIBCPP_INLINE_VISIBILITY constexpr size_type size_bytes() const noexcept { return _Extent * sizeof(element_type); }
-    _LIBCPP_INLINE_VISIBILITY constexpr bool empty()           const noexcept { return _Extent == 0; }
+    _LIBCPP_INLINE_VISIBILITY constexpr size_type size()           const noexcept { return _Extent; }
+    _LIBCPP_INLINE_VISIBILITY constexpr size_type size_bytes()     const noexcept { return _Extent * sizeof(element_type); }
+    [[nodiscard]] _LIBCPP_INLINE_VISIBILITY constexpr bool empty() const noexcept { return _Extent == 0; }
 
     _LIBCPP_INLINE_VISIBILITY constexpr reference operator[](size_type __idx) const noexcept
     {
@@ -501,9 +501,9 @@ public:
         return {data() + __offset, __count};
     }
 
-    _LIBCPP_INLINE_VISIBILITY constexpr size_type size()       const noexcept { return __size; }
-    _LIBCPP_INLINE_VISIBILITY constexpr size_type size_bytes() const noexcept { return __size * sizeof(element_type); }
-    _LIBCPP_INLINE_VISIBILITY constexpr bool empty()           const noexcept { return __size == 0; }
+    _LIBCPP_INLINE_VISIBILITY constexpr size_type size()           const noexcept { return __size; }
+    _LIBCPP_INLINE_VISIBILITY constexpr size_type size_bytes()     const noexcept { return __size * sizeof(element_type); }
+    [[nodiscard]] _LIBCPP_INLINE_VISIBILITY constexpr bool empty() const noexcept { return __size == 0; }
 
     _LIBCPP_INLINE_VISIBILITY constexpr reference operator[](size_type __idx) const noexcept
     {

diff  --git a/libcxx/test/std/containers/views/span.obs/empty.nodiscard.verify.cpp b/libcxx/test/std/containers/views/span.obs/empty.nodiscard.verify.cpp
new file mode 100644
index 000000000000..a6cb4792b92b
--- /dev/null
+++ b/libcxx/test/std/containers/views/span.obs/empty.nodiscard.verify.cpp
@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-has-no-incomplete-ranges
+
+// <span>
+
+// [[nodiscard]] constexpr bool empty() const noexcept;
+
+#include <span>
+
+void test() {
+  std::span<int> s1;
+  s1.empty(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+
+  int arr[] = {1, 2, 3};
+  std::span<int, 3> s2{arr};
+  s2.empty(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+}

diff  --git a/libcxx/test/std/containers/views/span.obs/empty.pass.cpp b/libcxx/test/std/containers/views/span.obs/empty.pass.cpp
index a03db7760366..5a86aaea607c 100644
--- a/libcxx/test/std/containers/views/span.obs/empty.pass.cpp
+++ b/libcxx/test/std/containers/views/span.obs/empty.pass.cpp
@@ -13,7 +13,7 @@
 
 // <span>
 
-// constexpr bool empty() const noexcept;
+// [[nodiscard]] constexpr bool empty() const noexcept;
 //