[libc++] Removes __cpp_lib_monadic_optional.

[Mordante]

Summary

P0798R8 "Monadic operations for std::optional" has been implemented, so
this LWG issue can be adopted.

During review it was discovered another paper bumped the macro. The
part affecting optional of this paper is done, the variant isn't. The
status page is updated to reflect the current state.

Implements

• LWG 3621 Remove feature-test macro __cpp_lib_monadic_optional

Updates status of

• P2231R1 Missing constexpr in std::optional and std::variant

[philnik]

libcxx/utils/generate_feature_test_macro_components.py

496

The LWG issue says that 202106L is replaced with 202110L. Do you know what 202106L is?

[Mordante]

libcxx/utils/generate_feature_test_macro_components.py

496

ISO Standards only have one version, when a new version is released older versions are obsolete. In C++17 optional was added to the Standard with 202106L (I didn't validate that). Now the Standard updates it to 202110L. In libc++ we still want to use 202106L when compiled with C++17 or C++20. When the user uses C++2b it should be 202110L.

The same happened to __cpp_lib_string_view.

[philnik]

libcxx/utils/generate_feature_test_macro_components.py

496

I understand that part. I wanted to know if we have implemented the feature that bumped the version to 202106L.

[Mordante]

libcxx/utils/generate_feature_test_macro_components.py

496

I assume you mean bumped to 202110L. In D113408 you implemented it ;-)

[Mordante]

Addresses review comment.
It seems optional had another change in C++20. This change was done, but not
marked as complete since the same paper also updates variant, which hasn't been
implemented yet.

[philnik]

LGTM with CI passing.

[ldionne]

libcxx/include/optional

96 ↗

(On Diff #430149)

Those are conditionally explicit, so we should either use EXPLICIT or explicit(see-below) to show that they are not just explicit.

[philnik]

libcxx/include/optional

96 ↗

(On Diff #430149)

I think explicit(see-below) is the way to go here. I never would have guessed that EXPLICIT says that the explicit is conditional.

[Mordante]

Thanks for the review!

libcxx/docs/FeatureTestMacroTable.rst

.. table:: Current Status
     ``__cpp_lib_constexpr_cmath``                     *unimplemented*
     ------------------------------------------------- -----------------
     ``__cpp_lib_constexpr_typeinfo``                  *unimplemented*
     ------------------------------------------------- -----------------
     ``__cpp_lib_invoke_r``                            *unimplemented*
     ------------------------------------------------- -----------------
     ``__cpp_lib_is_scoped_enum``                      ``202011L``
     ------------------------------------------------- -----------------
-    ``__cpp_lib_monadic_optional``                    ``202110L``
-    ------------------------------------------------- -----------------
     ``__cpp_lib_move_only_function``                  *unimplemented*
     ------------------------------------------------- -----------------
+    ``__cpp_lib_optional``                            ``202110L``
+    ------------------------------------------------- -----------------
     ``__cpp_lib_out_ptr``                             *unimplemented*
     ------------------------------------------------- -----------------
     ``__cpp_lib_ranges_chunk``                        *unimplemented*
     ------------------------------------------------- -----------------
     ``__cpp_lib_ranges_chunk_by``                     *unimplemented*
     ------------------------------------------------- -----------------
     ``__cpp_lib_ranges_iota``                         *unimplemented*
     ------------------------------------------------- -----------------

libcxx/docs/Status/Cxx2bIssues.csv

 "`3598 <https://wg21.link/LWG3598>`__","``system_category().default_error_condition(0)`` is underspecified","February 2022","",""
 "`3601 <https://wg21.link/LWG3601>`__","common_iterator's postfix-proxy needs ``indirectly_readable`` ","February 2022","","","|ranges|"
 "`3607 <https://wg21.link/LWG3607>`__","``contiguous_iterator`` should not be allowed to have custom ``iter_move`` and ``iter_swap`` behavior","February 2022","|Nothing to do|","","|ranges|"
 "`3610 <https://wg21.link/LWG3610>`__","``iota_view::size`` sometimes rejects integer-class types","February 2022","","","|ranges|"
 "`3612 <https://wg21.link/LWG3612>`__","Inconsistent pointer alignment in ``std::format`` ","February 2022","|Complete|","14.0","|format|"
 "`3616 <https://wg21.link/LWG3616>`__","LWG 3498 seems to miss the non-member ``swap`` for ``basic_syncbuf`` ","February 2022","",""
 "`3618 <https://wg21.link/LWG3618>`__","Unnecessary ``iter_move`` for ``transform_view::iterator`` ","February 2022","","","|ranges|"
 "`3619 <https://wg21.link/LWG3619>`__","Specification of ``vformat_to`` contains ill-formed ``formatted_size`` calls","February 2022","|Nothing to do|","","|format|"
-"`3621 <https://wg21.link/LWG3621>`__","Remove feature-test macro ``__cpp_lib_monadic_optional`` ","February 2022","",""
+"`3621 <https://wg21.link/LWG3621>`__","Remove feature-test macro ``__cpp_lib_monadic_optional`` ","February 2022","|Complete|","15.0"
 "`3632 <https://wg21.link/LWG3632>`__","``unique_ptr`` ""Mandates: This constructor is not selected by class template argument deduction""","February 2022","|Nothing to do|",""
 "`3643 <https://wg21.link/LWG3643>`__","Missing ``constexpr`` in ``std::counted_iterator`` ","February 2022","",""
 "`3648 <https://wg21.link/LWG3648>`__","``format`` should not print ``bool`` with ``'c'`` ","February 2022","|Complete|","15.0","|format|"
 "`3649 <https://wg21.link/LWG3649>`__","[fund.ts.v2] Reinstate and bump ``__cpp_lib_experimental_memory_resource`` feature test macro","February 2022","",""
 "`3650 <https://wg21.link/LWG3650>`__","Are ``std::basic_string`` 's ``iterator`` and ``const_iterator`` constexpr iterators?","February 2022","|Nothing to do|",""
 "`3654 <https://wg21.link/LWG3654>`__","``basic_format_context::arg(size_t)`` should be ``noexcept`` ","February 2022","|Complete|","15.0","|format|"
 "`3657 <https://wg21.link/LWG3657>`__","``std::hash<std::filesystem::path>`` is not enabled","February 2022","",""
 "`3660 <https://wg21.link/LWG3660>`__","``iterator_traits<common_iterator>::pointer`` should conform to §[iterator.traits]","February 2022","|Complete|","14.0"
 "`3661 <https://wg21.link/LWG3661>`__","``constinit atomic<shared_ptr<T>> a(nullptr);`` should work","February 2022","",""
 "","","","",""
 "`3645 <https://wg21.link/LWG3645>`__","``resize_and_overwrite`` is overspecified to call its callback with lvalues","Not voted in","|Complete|","14.0",""
 "`3656 <https://wg21.link/LWG3656>`__","Inconsistent bit operations returning a count","Not voted in","|Complete|","15.0",""
 "","","","",""

libcxx/include/version

 __cpp_lib_logical_traits                                201510L <type_traits>
 __cpp_lib_make_from_tuple                               201606L <tuple>
 __cpp_lib_make_reverse_iterator                         201402L <iterator>
 __cpp_lib_make_unique                                   201304L <memory>
 __cpp_lib_map_try_emplace                               201411L <map>
 __cpp_lib_math_constants                                201907L <numbers>
 __cpp_lib_math_special_functions                        201603L <cmath>
 __cpp_lib_memory_resource                               201603L <memory_resource>
-__cpp_lib_monadic_optional                              202110L <optional>
 __cpp_lib_move_only_function                            202110L <functional>
 __cpp_lib_node_extract                                  201606L <map> <set> <unordered_map>
                                                                 <unordered_set>
 __cpp_lib_nonmember_container_access                    201411L <array> <deque> <forward_list>
                                                                 <iterator> <list> <map>
                                                                 <regex> <set> <string>
                                                                 <unordered_map> <unordered_set> <vector>
 __cpp_lib_not_fn                                        201603L <functional>
 __cpp_lib_null_iterators                                201304L <iterator>
-__cpp_lib_optional                                      201606L <optional>
+__cpp_lib_optional                                      202110L <optional>
+                                                        201606L // C++17
 __cpp_lib_out_ptr                                       202106L <memory>
 __cpp_lib_parallel_algorithm                            201603L <algorithm> <numeric>
 __cpp_lib_polymorphic_allocator                         201902L <memory_resource>
 __cpp_lib_quoted_string_io                              201304L <iomanip>
 __cpp_lib_ranges                                        201811L <algorithm> <functional> <iterator>
                                                                 <memory> <ranges>
 __cpp_lib_ranges_chunk                                  202202L <ranges>
 __cpp_lib_ranges_chunk_by                               202202L <ranges>

 # define __cpp_lib_allocate_at_least                    202106L
 // # define __cpp_lib_associative_heterogeneous_erasure    202110L
 // # define __cpp_lib_bind_back                            202202L
 # define __cpp_lib_byteswap                             202110L
 // # define __cpp_lib_constexpr_cmath                      202202L
 // # define __cpp_lib_constexpr_typeinfo                   202106L
 // # define __cpp_lib_invoke_r                             202106L
 # define __cpp_lib_is_scoped_enum                       202011L
-# define __cpp_lib_monadic_optional                     202110L
 // # define __cpp_lib_move_only_function                   202110L
+# undef  __cpp_lib_optional
+# define __cpp_lib_optional                             202110L
 // # define __cpp_lib_out_ptr                              202106L
 // # define __cpp_lib_ranges_chunk                         202202L
 // # define __cpp_lib_ranges_chunk_by                      202202L
 // # define __cpp_lib_ranges_iota                          202202L
 // # define __cpp_lib_ranges_join_with                     202202L
 // # define __cpp_lib_ranges_slide                         202202L
 // # define __cpp_lib_ranges_starts_ends_with              202106L
 // # define __cpp_lib_ranges_to_container                  202202L

libcxx/test/std/language.support/support.limits/support.limits.general/optional.version.compile.pass.cpp

 // and should not be edited manually.
 //
 // clang-format off
 
 // <optional>
 
 // Test the feature test macros defined by <optional>
 
-/*  Constant                      Value
-    __cpp_lib_monadic_optional    202110L [C++2b]
-    __cpp_lib_optional            201606L [C++17]
+/*  Constant              Value
+    __cpp_lib_optional    201606L [C++17]
+                          202110L [C++2b]
 */
 
 #include <optional>
 #include "test_macros.h"
 
 #if TEST_STD_VER < 14
 
-# ifdef __cpp_lib_monadic_optional
-#   error "__cpp_lib_monadic_optional should not be defined before c++2b"
-# endif
-
 # ifdef __cpp_lib_optional
 #   error "__cpp_lib_optional should not be defined before c++17"
 # endif
 
 #elif TEST_STD_VER == 14
 
-# ifdef __cpp_lib_monadic_optional
-#   error "__cpp_lib_monadic_optional should not be defined before c++2b"
-# endif
-
 # ifdef __cpp_lib_optional
 #   error "__cpp_lib_optional should not be defined before c++17"
 # endif
 
 #elif TEST_STD_VER == 17
 
-# ifdef __cpp_lib_monadic_optional
-#   error "__cpp_lib_monadic_optional should not be defined before c++2b"
-# endif
-
 # ifndef __cpp_lib_optional
 #   error "__cpp_lib_optional should be defined in c++17"
 # endif
 # if __cpp_lib_optional != 201606L
 #   error "__cpp_lib_optional should have the value 201606L in c++17"
 # endif
 
 #elif TEST_STD_VER == 20
 
-# ifdef __cpp_lib_monadic_optional
-#   error "__cpp_lib_monadic_optional should not be defined before c++2b"
-# endif
-
 # ifndef __cpp_lib_optional
 #   error "__cpp_lib_optional should be defined in c++20"
 # endif
 # if __cpp_lib_optional != 201606L
 #   error "__cpp_lib_optional should have the value 201606L in c++20"
 # endif
 
 #elif TEST_STD_VER > 20
 
-# ifndef __cpp_lib_monadic_optional
-#   error "__cpp_lib_monadic_optional should be defined in c++2b"
-# endif
-# if __cpp_lib_monadic_optional != 202110L
-#   error "__cpp_lib_monadic_optional should have the value 202110L in c++2b"
-# endif
-
 # ifndef __cpp_lib_optional
 #   error "__cpp_lib_optional should be defined in c++2b"
 # endif
-# if __cpp_lib_optional != 201606L
-#   error "__cpp_lib_optional should have the value 201606L in c++2b"
+# if __cpp_lib_optional != 202110L
+#   error "__cpp_lib_optional should have the value 202110L in c++2b"
 # endif
 
 #endif // TEST_STD_VER > 20
 

libcxx/test/std/language.support/support.limits/support.limits.general/version.version.compile.pass.cpp

/*  Constant                                       Value
     __cpp_lib_logical_traits                       201510L [C++17]
     __cpp_lib_make_from_tuple                      201606L [C++17]
     __cpp_lib_make_reverse_iterator                201402L [C++14]
     __cpp_lib_make_unique                          201304L [C++14]
     __cpp_lib_map_try_emplace                      201411L [C++17]
     __cpp_lib_math_constants                       201907L [C++20]
     __cpp_lib_math_special_functions               201603L [C++17]
     __cpp_lib_memory_resource                      201603L [C++17]
-    __cpp_lib_monadic_optional                     202110L [C++2b]
     __cpp_lib_move_only_function                   202110L [C++2b]
     __cpp_lib_node_extract                         201606L [C++17]
     __cpp_lib_nonmember_container_access           201411L [C++17]
     __cpp_lib_not_fn                               201603L [C++17]
     __cpp_lib_null_iterators                       201304L [C++14]
     __cpp_lib_optional                             201606L [C++17]
+                                                   202110L [C++2b]
     __cpp_lib_out_ptr                              202106L [C++2b]
     __cpp_lib_parallel_algorithm                   201603L [C++17]
     __cpp_lib_polymorphic_allocator                201902L [C++20]
     __cpp_lib_quoted_string_io                     201304L [C++14]
     __cpp_lib_ranges                               201811L [C++20]
     __cpp_lib_ranges_chunk                         202202L [C++2b]
     __cpp_lib_ranges_chunk_by                      202202L [C++2b]
     __cpp_lib_ranges_iota                          202202L [C++2b]

 # ifdef __cpp_lib_math_special_functions
 #   error "__cpp_lib_math_special_functions should not be defined before c++17"
 # endif
 
 # ifdef __cpp_lib_memory_resource
 #   error "__cpp_lib_memory_resource should not be defined before c++17"
 # endif
 
-# ifdef __cpp_lib_monadic_optional
-#   error "__cpp_lib_monadic_optional should not be defined before c++2b"
-# endif
-
 # ifdef __cpp_lib_move_only_function
 #   error "__cpp_lib_move_only_function should not be defined before c++2b"
 # endif
 
 # ifdef __cpp_lib_node_extract
 #   error "__cpp_lib_node_extract should not be defined before c++17"
 # endif
 

 # ifdef __cpp_lib_math_special_functions
 #   error "__cpp_lib_math_special_functions should not be defined before c++17"
 # endif
 
 # ifdef __cpp_lib_memory_resource
 #   error "__cpp_lib_memory_resource should not be defined before c++17"
 # endif
 
-# ifdef __cpp_lib_monadic_optional
-#   error "__cpp_lib_monadic_optional should not be defined before c++2b"
-# endif
-
 # ifdef __cpp_lib_move_only_function
 #   error "__cpp_lib_move_only_function should not be defined before c++2b"
 # endif
 
 # ifdef __cpp_lib_node_extract
 #   error "__cpp_lib_node_extract should not be defined before c++17"
 # endif
 

 #     error "__cpp_lib_memory_resource should have the value 201603L in c++17"
 #   endif
 # else // _LIBCPP_VERSION
 #   ifdef __cpp_lib_memory_resource
 #     error "__cpp_lib_memory_resource should not be defined because it is unimplemented in libc++!"
 #   endif
 # endif
 
-# ifdef __cpp_lib_monadic_optional
-#   error "__cpp_lib_monadic_optional should not be defined before c++2b"
-# endif
-
 # ifdef __cpp_lib_move_only_function
 #   error "__cpp_lib_move_only_function should not be defined before c++2b"
 # endif
 
 # ifndef __cpp_lib_node_extract
 #   error "__cpp_lib_node_extract should be defined in c++17"
 # endif
 # if __cpp_lib_node_extract != 201606L

 #     error "__cpp_lib_memory_resource should have the value 201603L in c++20"
 #   endif
 # else // _LIBCPP_VERSION
 #   ifdef __cpp_lib_memory_resource
 #     error "__cpp_lib_memory_resource should not be defined because it is unimplemented in libc++!"
 #   endif
 # endif
 
-# ifdef __cpp_lib_monadic_optional
-#   error "__cpp_lib_monadic_optional should not be defined before c++2b"
-# endif
-
 # ifdef __cpp_lib_move_only_function
 #   error "__cpp_lib_move_only_function should not be defined before c++2b"
 # endif
 
 # ifndef __cpp_lib_node_extract
 #   error "__cpp_lib_node_extract should be defined in c++20"
 # endif
 # if __cpp_lib_node_extract != 201606L

 #     error "__cpp_lib_memory_resource should have the value 201603L in c++2b"
 #   endif
 # else // _LIBCPP_VERSION
 #   ifdef __cpp_lib_memory_resource
 #     error "__cpp_lib_memory_resource should not be defined because it is unimplemented in libc++!"
 #   endif
 # endif
 
-# ifndef __cpp_lib_monadic_optional
-#   error "__cpp_lib_monadic_optional should be defined in c++2b"
-# endif
-# if __cpp_lib_monadic_optional != 202110L
-#   error "__cpp_lib_monadic_optional should have the value 202110L in c++2b"
-# endif
-
 # if !defined(_LIBCPP_VERSION)
 #   ifndef __cpp_lib_move_only_function
 #     error "__cpp_lib_move_only_function should be defined in c++2b"
 #   endif
 #   if __cpp_lib_move_only_function != 202110L
 #     error "__cpp_lib_move_only_function should have the value 202110L in c++2b"
 #   endif
 # else // _LIBCPP_VERSION

 # endif
 # if __cpp_lib_null_iterators != 201304L
 #   error "__cpp_lib_null_iterators should have the value 201304L in c++2b"
 # endif
 
 # ifndef __cpp_lib_optional
 #   error "__cpp_lib_optional should be defined in c++2b"
 # endif
-# if __cpp_lib_optional != 201606L
-#   error "__cpp_lib_optional should have the value 201606L in c++2b"
+# if __cpp_lib_optional != 202110L
+#   error "__cpp_lib_optional should have the value 202110L in c++2b"
 # endif
 
 # if !defined(_LIBCPP_VERSION)
 #   ifndef __cpp_lib_out_ptr
 #     error "__cpp_lib_out_ptr should be defined in c++2b"
 #   endif
 #   if __cpp_lib_out_ptr != 202106L
 #     error "__cpp_lib_out_ptr should have the value 202106L in c++2b"

libcxx/utils/generate_feature_test_macro_components.py

feature_test_macros = [ add_version_header(x) for x in [
     "headers": ["cmath"],
     "unimplemented": True,
   }, {
     "name": "__cpp_lib_memory_resource",
     "values": { "c++17": 201603 },
     "headers": ["memory_resource"],
     "unimplemented": True,
   }, {
-    "name": "__cpp_lib_monadic_optional",
-    "values": { "c++2b": 202110 },
-    "headers": ["optional"],
-  }, {
     "name": "__cpp_lib_move_only_function",
     "values": { "c++2b": 202110 },
     "headers": ["functional"],
     "unimplemented": True,
   }, {
     "name": "__cpp_lib_node_extract",
     "values": { "c++17": 201606 },
     "headers": ["map", "set", "unordered_map", "unordered_set"],
   }, {
     "name": "__cpp_lib_nonmember_container_access",
     "values": { "c++17": 201411 },
     "headers": ["array", "deque", "forward_list", "iterator", "list", "map", "regex", "set", "string", "unordered_map", "unordered_set", "vector"],
   }, {
     "name": "__cpp_lib_not_fn",
     "values": { "c++17": 201603 },
     "headers": ["functional"],
   }, {
     "name": "__cpp_lib_null_iterators",
     "values": { "c++14": 201304 },
     "headers": ["iterator"],
   }, {
     "name": "__cpp_lib_optional",
-    "values": { "c++17": 201606 },
+    "values": { "c++17": 201606, "c++2b": 202110 },
     "headers": ["optional"],
   }, {
     "name": "__cpp_lib_out_ptr",
     "values": { "c++2b": 202106 },
     "headers": ["memory"],
     "unimplemented": True,
   }, {
     "name": "__cpp_lib_parallel_algorithm",