[committed] libstdc++: Ensure std::span and std::string_view are trivially copyable (P2251R1)

[Jonathan Wakely via Gcc-patches]

The recently approved P2251R1 paper requires these types to be trivially
copyable. They always have been in libstdc++, but add tests to check it.

libstdc++-v3/ChangeLog:

        * 
testsuite/21_strings/basic_string_view/requirements/trivially_copyable.cc:
        New test.
        * testsuite/23_containers/span/trivially_copyable.cc: New test.

Tested x86_64-linux. Committed to trunk.


commit 1f51e9af7b615838424214e6aaea0de793cb10fe
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Tue Oct 5 16:38:42 2021

    libstdc++: Ensure std::span and std::string_view are trivially copyable 
(P2251R1)
    
    The recently approved P2251R1 paper requires these types to be trivially
    copyable. They always have been in libstdc++, but add tests to check it.
    
    libstdc++-v3/ChangeLog:
    
            * 
testsuite/21_strings/basic_string_view/requirements/trivially_copyable.cc:
            New test.
            * testsuite/23_containers/span/trivially_copyable.cc: New test.

diff --git 
a/libstdc++-v3/testsuite/21_strings/basic_string_view/requirements/trivially_copyable.cc
 
b/libstdc++-v3/testsuite/21_strings/basic_string_view/requirements/trivially_copyable.cc
new file mode 100644
index 00000000000..3f2589c61d8
--- /dev/null
+++ 
b/libstdc++-v3/testsuite/21_strings/basic_string_view/requirements/trivially_copyable.cc
@@ -0,0 +1,11 @@
+// { dg-do compile { target c++17 } }
+
+// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2251r1.pdf
+
+#include <string_view>
+
+static_assert( std::is_trivially_copyable_v<std::string_view> );
+static_assert( std::is_trivially_copyable_v<std::wstring_view> );
+
+struct traits : std::char_traits<char> { };
+static_assert( std::is_trivially_copyable_v<std::basic_string_view<char, 
traits>> );
diff --git a/libstdc++-v3/testsuite/23_containers/span/trivially_copyable.cc 
b/libstdc++-v3/testsuite/23_containers/span/trivially_copyable.cc
new file mode 100644
index 00000000000..e3748293555
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/span/trivially_copyable.cc
@@ -0,0 +1,13 @@
+// { dg-options "-std=gnu++20" }
+// { dg-do compile { target c++20 } }
+
+// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2251r1.pdf
+
+#include <span>
+
+static_assert( std::is_trivially_copyable_v<std::span<int>> );
+static_assert( std::is_trivially_copyable_v<std::span<int, 42>> );
+
+struct NonTrivial { NonTrivial(); NonTrivial(const NonTrivial&); };
+static_assert( std::is_trivially_copyable_v<std::span<NonTrivial>> );
+static_assert( std::is_trivially_copyable_v<std::span<NonTrivial, 99>> );