[libcxx] __cpp_lib_ranges value should be 201911L under C++20, not 201811L

[ldionne]

Summary

This breaks my code since my code detects __cpp_lib_ranges >= 201911L

I have checked cppreference, libstdc++, msvc stl, they all define __cpp_lib_ranges as 201911L. Clearly this is a bug.

Test runs successfully locally

[expnkx]

ALso i find that __cpp_lib_ranges macro is not defined at all. do not know why

[• Quuxplusone]

libcxx/utils/generate_feature_test_macro_components.py

491–494

I think this change from 201811 to 201911 is correct. I'm willing to commandeer and land this 1-character-plus-autogenerated-files change. @ldionne, thoughts?
https://timsong-cpp.github.io/cppwp/n4861/version.syn#lib:__cpp_lib_ranges

However, notice the "unimplemented": True. That's correct as-is, because libc++ does not yet fully implement C++20 Ranges. We'll define the feature-test macro only once we have implemented the feature; that's what it's for!

[Mordante]

@expnkx please don't remove libc++ group for libc++ patches and please don't self approve.

libcxx/utils/generate_feature_test_macro_components.py

491–494

IMO we should only bump it when we start/have started to work on the papers that increment this value. It might be we finish the part that requires 201811 before we finish the papers that required 201911.

[• Quuxplusone]

libcxx/utils/generate_feature_test_macro_components.py

491–494

Oh, [p0896] actually did set it to 201811 (and confirmed by p1458r1)! Okay then.
I wish there were an authoritative list of all possible feature-test macro values and what they mean. The closest I know of is https://en.cppreference.com/w/cpp/feature_test but it doesn't list things at paper granularity, like, [p0896]; it lists only what the value is for each released standard (like, C++20 as a whole). For example, that page doesn't list 201811 as a possible value for __cpp_lib_ranges (presumably because no International Standard was ever released with that specific value).

That said, given that there's no authoritative source for what 201811 is supposed to mean, I'm also not sure how we'd ever figure out that it's okay to bump libc++'s macro value from unimplemented to implemented, let alone from 201811 to 201911. The only 100% safe thing I can see is that once we've implemented 100% of the C++20 IS, then we can definitely bump it to 201911 because that's what the C++20 IS says it should be.

[Mordante]

libcxx/utils/generate_feature_test_macro_components.py

491–494

There's an authoritative source. That's the paper that changed the version number. I'm not aware of a location where that information can easily be found. So I hope the people working on implementing the papers keep track of it. For <format> I know which 3 papers give a version bump. (Fun fact C++20 format will get a feature-test macro with the value of 202110 due to a paper being retroactively applied to C++20 at the last plenary.)

[ldionne]

[Github PR transition cleanup]

This isn't relevant anymore since we now have:

{
    "name": "__cpp_lib_ranges",
    "values": {"c++20": 202207},
    "headers": ["algorithm", "functional", "iterator", "memory", "ranges"],
},

Commandeering and closing.

libcxx/include/version

 __cpp_lib_parallel_algorithm                            201603L <algorithm> <numeric>
 __cpp_lib_polymorphic_allocator                         201902L <memory>
 __cpp_lib_quoted_string_io                              201304L <iomanip>
-__cpp_lib_ranges                                        201811L <algorithm> <functional> <iterator>
+__cpp_lib_ranges                                        201911L <algorithm> <functional> <iterator>
                                                                 <memory> <ranges>
 __cpp_lib_raw_memory_algorithms                         201606L <memory>
 __cpp_lib_remove_cvref                                  201711L <type_traits>

 #   define __cpp_lib_math_constants                     201907L
 # endif
 // # define __cpp_lib_polymorphic_allocator                201902L
-// # define __cpp_lib_ranges                               201811L
+// # define __cpp_lib_ranges                               201911L
 # define __cpp_lib_remove_cvref                         201711L
 # if !defined(_LIBCPP_HAS_NO_THREADS) && !defined(_LIBCPP_AVAILABILITY_DISABLE_FTM___cpp_lib_semaphore)
 #   define __cpp_lib_semaphore                          201907L

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

     __cpp_lib_make_reverse_iterator         201402L [C++14]
     __cpp_lib_nonmember_container_access    201411L [C++17]
     __cpp_lib_null_iterators                201304L [C++14]
-    __cpp_lib_ranges                        201811L [C++20]
+    __cpp_lib_ranges                        201911L [C++20]
     __cpp_lib_ssize                         201902L [C++20]
 */
 

 #   ifndef __cpp_lib_ranges
 #     error "__cpp_lib_ranges should be defined in c++20"
 #   endif
-#   if __cpp_lib_ranges != 201811L
-#     error "__cpp_lib_ranges should have the value 201811L in c++20"
+#   if __cpp_lib_ranges != 201911L
+#     error "__cpp_lib_ranges should have the value 201911L in c++20"
 #   endif
 # else // _LIBCPP_VERSION
 #   ifdef __cpp_lib_ranges

 #   ifndef __cpp_lib_ranges
 #     error "__cpp_lib_ranges should be defined in c++2b"
 #   endif
-#   if __cpp_lib_ranges != 201811L
-#     error "__cpp_lib_ranges should have the value 201811L in c++2b"
+#   if __cpp_lib_ranges != 201911L
+#     error "__cpp_lib_ranges should have the value 201911L in c++2b"
 #   endif
 # else // _LIBCPP_VERSION
 #   ifdef __cpp_lib_ranges

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

 // Test the feature test macros defined by <ranges>
 
 /*  Constant            Value
-    __cpp_lib_ranges    201811L [C++20]
+    __cpp_lib_ranges    201911L [C++20]
 */
 
 #include <ranges>

 #   ifndef __cpp_lib_ranges
 #     error "__cpp_lib_ranges should be defined in c++20"
 #   endif
-#   if __cpp_lib_ranges != 201811L
-#     error "__cpp_lib_ranges should have the value 201811L in c++20"
+#   if __cpp_lib_ranges != 201911L
+#     error "__cpp_lib_ranges should have the value 201911L in c++20"
 #   endif
 # else // _LIBCPP_VERSION
 #   ifdef __cpp_lib_ranges

 #   ifndef __cpp_lib_ranges
 #     error "__cpp_lib_ranges should be defined in c++2b"
 #   endif
-#   if __cpp_lib_ranges != 201811L
-#     error "__cpp_lib_ranges should have the value 201811L in c++2b"
+#   if __cpp_lib_ranges != 201911L
+#     error "__cpp_lib_ranges should have the value 201911L in c++2b"
 #   endif
 # else // _LIBCPP_VERSION
 #   ifdef __cpp_lib_ranges

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

     __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                               201911L [C++20]
     __cpp_lib_raw_memory_algorithms                201606L [C++17]
     __cpp_lib_remove_cvref                         201711L [C++20]
     __cpp_lib_result_of_sfinae                     201210L [C++14]

 #   ifndef __cpp_lib_ranges
 #     error "__cpp_lib_ranges should be defined in c++20"
 #   endif
-#   if __cpp_lib_ranges != 201811L
-#     error "__cpp_lib_ranges should have the value 201811L in c++20"
+#   if __cpp_lib_ranges != 201911L
+#     error "__cpp_lib_ranges should have the value 201911L in c++20"
 #   endif
 # else // _LIBCPP_VERSION
 #   ifdef __cpp_lib_ranges

 #   ifndef __cpp_lib_ranges
 #     error "__cpp_lib_ranges should be defined in c++2b"
 #   endif
-#   if __cpp_lib_ranges != 201811L
-#     error "__cpp_lib_ranges should have the value 201811L in c++2b"
+#   if __cpp_lib_ranges != 201911L
+#     error "__cpp_lib_ranges should have the value 201911L in c++2b"
 #   endif
 # else // _LIBCPP_VERSION
 #   ifdef __cpp_lib_ranges

libcxx/utils/generate_feature_test_macro_components.py

     "headers": ["iomanip"],
   }, {
     "name": "__cpp_lib_ranges",
-    "values": { "c++20": 201811 },
+    "values": { "c++20": 201911 },
     "headers": ["algorithm", "functional", "iterator", "memory", "ranges"],
     "unimplemented": True,
   }, {