Fix layout stride converting explicit clause (#445)

* add compile test for constructibility, implicit convertability, and assignability for strided layouts

* add padded layouts to explicit clause in strided layout converting constructor

* don't check padded layout to strided layout conversion in < C++17

* address review

Author: nmm0

compilation_tests/ctest_layout_convertible.cpp

@@ -91,4 +91,24 @@ MDSPAN_STATIC_TEST(
   !std::is_constructible<LS1, NotARealLayout::mapping<E2>>::value
 );
 
-
+MDSPAN_STATIC_TEST(std::is_constructible<LS1, Kokkos::layout_left::mapping<E1>>::value);
+MDSPAN_STATIC_TEST(std::is_convertible<Kokkos::layout_left::mapping<E1>, LS1>::value);
+MDSPAN_STATIC_TEST(std::is_assignable<LS1, Kokkos::layout_left::mapping<E1>>::value);
+
+MDSPAN_STATIC_TEST(std::is_constructible<LS1, Kokkos::layout_right::mapping<E1>>::value);
+MDSPAN_STATIC_TEST(std::is_convertible<Kokkos::layout_right::mapping<E1>, LS1>::value);
+MDSPAN_STATIC_TEST(std::is_assignable<LS1, Kokkos::layout_right::mapping<E1>>::value);
+
+MDSPAN_STATIC_TEST(std::is_constructible<LS1, Kokkos::layout_stride::mapping<E1>>::value);
+MDSPAN_STATIC_TEST(std::is_convertible<Kokkos::layout_stride::mapping<E1>, LS1>::value);
+MDSPAN_STATIC_TEST(std::is_assignable<LS1, Kokkos::layout_stride::mapping<E1>>::value);
+
+#if MDSPAN_HAS_CXX_17
+MDSPAN_STATIC_TEST(std::is_constructible<LS1, Kokkos::Experimental::layout_left_padded<14>::mapping<E1>>::value);
+MDSPAN_STATIC_TEST(std::is_convertible<Kokkos::Experimental::layout_left_padded<14>::mapping<E1>, LS1>::value);
+MDSPAN_STATIC_TEST(std::is_assignable<LS1, Kokkos::Experimental::layout_left_padded<14>::mapping<E1>>::value);
+
+MDSPAN_STATIC_TEST(std::is_constructible<LS1, Kokkos::Experimental::layout_right_padded<14>::mapping<E1>>::value);
+MDSPAN_STATIC_TEST(std::is_convertible<Kokkos::Experimental::layout_right_padded<14>::mapping<E1>, LS1>::value);
+MDSPAN_STATIC_TEST(std::is_assignable<LS1, Kokkos::Experimental::layout_right_padded<14>::mapping<E1>>::value);
+#endif

include/experimental/__p0009_bits/layout_stride.hpp

@@ -21,6 +21,10 @@
 #include "compressed_pair.hpp"
 #include "utility.hpp"
 
+#if MDSPAN_HAS_CXX_17
+#include "../__p2642_bits/layout_padded_fwd.hpp"
+#endif
+
 #if !defined(MDSPAN_IMPL_USE_ATTRIBUTE_NO_UNIQUE_ADDRESS)
 #  include "no_unique_address.hpp"
 #endif
@@ -441,6 +445,8 @@ struct layout_stride {
       !(std::is_convertible<typename StridedLayoutMapping::extents_type, extents_type>::value &&
        (detail::is_mapping_of<layout_left, StridedLayoutMapping> ||
         detail::is_mapping_of<layout_right, StridedLayoutMapping> ||
+        MDSPAN_IMPL_PROPOSED_NAMESPACE::detail::is_layout_left_padded_mapping<StridedLayoutMapping>::value || // Don't need to guard for C++14 as this isn't compiled in < C++20
+        MDSPAN_IMPL_PROPOSED_NAMESPACE::detail::is_layout_right_padded_mapping<StridedLayoutMapping>::value ||
         detail::is_mapping_of<layout_stride, StridedLayoutMapping>))
     ) // needs two () due to comma
     MDSPAN_INLINE_FUNCTION MDSPAN_IMPL_CONSTEXPR_14