Revert "[libc++] Re-enable std::pair trivial copy constructor for FreeBSD >= 14"

[jrtc27]

The ABI bump to adopt the conforming ABI v1 std::pair implementation did
not end up happening for FreeBSD 14, and instead this diff was reverted
downstream in FreeBSD[1]. Align the upstream ABI config with FreeBSD's
actual ABI.

[1] ce4f1f49e036 ("Revert commit 6255157 from llvm-project (by Dimitry Andric):")

This reverts commit 6255157.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Jessica Clarke (jrtc27)

Changes

The ABI bump to adopt the conforming ABI v1 std::pair implementation did
not end up happening for FreeBSD 14, and instead this diff was reverted
downstream in FreeBSD[1]. Align the upstream ABI config with FreeBSD's
actual ABI.

[1] ce4f1f49e036 ("Revert commit 6255157 from llvm-project (by Dimitry Andric):")

This reverts commit 6255157.

---

Full diff: https://github.com/llvm/llvm-project/pull/142204.diff

2 Files Affected:

• (modified) libcxx/include/__configuration/abi.h (+1-1)
• (modified) libcxx/include/__cxx03/__configuration/abi.h (+1-1)

diff --git a/libcxx/include/__configuration/abi.h b/libcxx/include/__configuration/abi.h
index 01a4a4c023983..cc4b930b3cf4a 100644
--- a/libcxx/include/__configuration/abi.h
+++ b/libcxx/include/__configuration/abi.h
@@ -130,7 +130,7 @@
 #  endif
 // Feature macros for disabling pre ABI v1 features. All of these options
 // are deprecated.
-#  if defined(__FreeBSD__) && __FreeBSD__ < 14
+#  if defined(__FreeBSD__)
 #    define _LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR
 #  endif
 #endif
diff --git a/libcxx/include/__cxx03/__configuration/abi.h b/libcxx/include/__cxx03/__configuration/abi.h
index 740aec39a3487..81dd5b1c59610 100644
--- a/libcxx/include/__cxx03/__configuration/abi.h
+++ b/libcxx/include/__cxx03/__configuration/abi.h
@@ -116,7 +116,7 @@
 #  endif
 // Feature macros for disabling pre ABI v1 features. All of these options
 // are deprecated.
-#  if defined(__FreeBSD__) && __FreeBSD__ < 14
+#  if defined(__FreeBSD__)
 #    define _LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR
 #  endif
 #endif

[jrtc27]

FYI @DimitryAndric @emaste

[DimitryAndric]

LGTM

[ldionne]

Out of curiosity, is there a plan to adopt it in FreeBSD 15 or later?

[DimitryAndric]

Originally the plan was to wait until libc++ bumped its official ABI to 2, then go with that instead, so as to avoid have to break the FreeBSD base system's ABI more than once. But for some reason libc++ has stayed in ABI v1 for years now. :)

I'd say that it depends on whether libc++ will ever ship ABI v2, if that is still another number of years out then it might make sense to at least break the std::pair ABI for FreeBSD 15. Which will involve bumping our libc++.so.1 to something higher, likely libc++.so.2. We've painted ourselves into a corner with that: if libc++ at some point ships ABI v2 and bumps its own soname to .2 it's going to be very confusing...