[libc++] Bump _LIBCPP_STD_VER to the next expected C++ version

[philnik]

Summary

We've decided to use _LIBCPP_STD_VER >= xy while discussing to change the constexpr macros, so let's finally bump the version macro to match that.

[Mordante]

We've decided to use _LIBCPP_STD_VER >= xy while discussing to change the constexpr macros, so let's finally bump the version macro to match that.

I don't recall that was decided during that in that review. Can you share the link where that decision was made? (Or remove that part of the commit message.)

Regardless of the objection above I still think this change is nice to have. Based on the track record of the committee I feel we can expect the 3 year cycle. (Even when 26 becomes 27 it will be a simple search and replace.)

A few nits otherwise LGTM. I feel more developers should have a look so I leave the final approval to them.

libcxx/include/__config

50

51

Please do the same for the test macro including the comment.

[philnik]

• Address comments

[philnik]

In D133323#3770792, @Mordante wrote:

We've decided to use _LIBCPP_STD_VER >= xy while discussing to change the constexpr macros, so let's finally bump the version macro to match that.

I don't recall that was decided during that in that review. Can you share the link where that decision was made? (Or remove that part of the commit message.)

I brought it up during the discussion on Discord and nobody objected, so I assumed everybody was OK with it. @avogelsgesang and @ldionne also explicitly asked about it there.

libcxx/include/__config

51

The test macro is defined as 99 currently, so we can already use TEST_STD_VER >= 23.

[avogelsgesang]

LGTM!

Are you planning to also replace existing usages of, e.g. #if _LIBCPP_STD_VER > 17 by #if _LIBCPP_STD_VER >= 20?

[huixie90]

LGTM

[ldionne]

In D133323#3771081, @avogelsgesang wrote:

Are you planning to also replace existing usages of, e.g. #if _LIBCPP_STD_VER > 17 by #if _LIBCPP_STD_VER >= 20?

I'm not sure that part is worth the churn. I'd welcome a patch, but depending on how crazy it ends up being, I think it might not be the best idea.

[Mordante]

In D133323#3771034, @philnik wrote:

In D133323#3770792, @Mordante wrote:

We've decided to use _LIBCPP_STD_VER >= xy while discussing to change the constexpr macros, so let's finally bump the version macro to match that.

I don't recall that was decided during that in that review. Can you share the link where that decision was made? (Or remove that part of the commit message.)

I brought it up during the discussion on Discord and nobody objected, so I assumed everybody was OK with it. @avogelsgesang and @ldionne also explicitly asked about it there.

I don't feel "I assumed everybody was OK with it" sounds as a discision.
I don't mind seeing it in new code. But rather not see existing code in, areas with a lot of active development, changed. Or changes that affect patches under review.

[mclow.lists]

libcxx/include/__config

51

Until C++23 is released, I would recommend not changing these macros.

The test macro is defined differently than the one in __config in an attempt to make it harder for people to depend on numbers that are not guaranteed to be stable.

The code XXX_STD_VER > 20 will work for all standard versions later than C++20.

[ldionne]

In D133323#3782371, @Mordante wrote:

In D133323#3771034, @philnik wrote:

In D133323#3770792, @Mordante wrote:

We've decided to use _LIBCPP_STD_VER >= xy while discussing to change the constexpr macros, so let's finally bump the version macro to match that.

I don't recall that was decided during that in that review. Can you share the link where that decision was made? (Or remove that part of the commit message.)

I brought it up during the discussion on Discord and nobody objected, so I assumed everybody was OK with it. @avogelsgesang and @ldionne also explicitly asked about it there.

I don't feel "I assumed everybody was OK with it" sounds as a discision.
I don't mind seeing it in new code. But rather not see existing code in, areas with a lot of active development, changed. Or changes that affect patches under review.

I do remember we had a discussion on Discord and several folks chimed in, but I don't remember exactly who did. My understanding after the discussion on Discord is that we were going to move forward with this approach. My understanding is also that I was the only one to oppose at the beginning.

[Mordante]

In D133323#3782870, @ldionne wrote:

In D133323#3782371, @Mordante wrote:

In D133323#3771034, @philnik wrote:

In D133323#3770792, @Mordante wrote:

We've decided to use _LIBCPP_STD_VER >= xy while discussing to change the constexpr macros, so let's finally bump the version macro to match that.

I don't recall that was decided during that in that review. Can you share the link where that decision was made? (Or remove that part of the commit message.)

I brought it up during the discussion on Discord and nobody objected, so I assumed everybody was OK with it. @avogelsgesang and @ldionne also explicitly asked about it there.

I don't feel "I assumed everybody was OK with it" sounds as a discision.
I don't mind seeing it in new code. But rather not see existing code in, areas with a lot of active development, changed. Or changes that affect patches under review.

I do remember we had a discussion on Discord and several folks chimed in, but I don't remember exactly who did. My understanding after the discussion on Discord is that we were going to move forward with this approach. My understanding is also that I was the only one to oppose at the beginning.

IMO then, for the future, we should make it clear whether we reached consensus and what the way forward is.
I would say a good way to do that is to update our libc++ developer documentation to reflect the new agreement.

AFAIK we only agreed to update the macro so we can use >= 23 but not require to use this new style. I really would like to have one style in one file and not to mix them in one file.

libcxx/include/__config

51

@mclow.lists For my curiosity can you tell why you don't recommend to change this macro?

libcxx/include/__config

 #      define _LIBCPP_STD_VER 11
 #    elif __cplusplus <= 201402L
 #      define _LIBCPP_STD_VER 14
 #    elif __cplusplus <= 201703L
 #      define _LIBCPP_STD_VER 17
 #    elif __cplusplus <= 202002L
 #      define _LIBCPP_STD_VER 20
 #    else
-#      define _LIBCPP_STD_VER 22 // current year, or date of c++2b ratification
+// Expected release year of the next C++ version
+#      define _LIBCPP_STD_VER 23
 #    endif
 #  endif // _LIBCPP_STD_VER
 
 #  if defined(__ELF__)
 #    define _LIBCPP_OBJECT_FORMAT_ELF 1
 #  elif defined(__MACH__)
 #    define _LIBCPP_OBJECT_FORMAT_MACHO 1
 #  elif defined(_WIN32)