Tests: Prepare for P2251 (trivially copyable `span`/`basic_string_view`) (#2015)

tests/std/tests/P0122R7_span/test.cpp

@@ -79,8 +79,8 @@ static_assert(ranges::enable_borrowed_range<span<int>>);
 static_assert(ranges::enable_borrowed_range<span<int, 3>>);
 #endif // __cpp_lib_concepts
 
-// For performance, our implementation provides an additional guarantee beyond the Standard
-// that span and its iterator types are trivially copyable.
+// We provide non-standard guarantees that span and its iterator types are trivially copyable;
+// P2251 may eventually standardize that guarantee for span itself.
 static_assert(is_trivially_copyable_v<span<int>>);
 static_assert(is_trivially_copyable_v<span<int>::iterator>);
 static_assert(is_trivially_copyable_v<span<int, 3>>);

tests/std/tests/P0220R1_string_view/test.cpp

@@ -67,6 +67,11 @@ const evil_conversion_to_string_view_lvalue_only convert_lvalue_only{};
 #pragma clang diagnostic pop
 #endif // __clang__
 
+// We provide a non-standard guarantee that basic_string_view is trivially copyable;
+// P2251 may eventually standardize that guarantee.
+static_assert(is_trivially_copyable_v<string_view>);
+static_assert(is_trivially_copyable_v<wstring_view>);
+
 // noexcept assertions:
 // (functions that explicitly throw have their throws tested and therefore have no static_asserts)
 static_assert(noexcept(string_view{}), "default constructor not noexcept");