[libc++] Remove _LIBCPP_ABI_UNSTABLE

Previously, _LIBCPP_ABI_UNSTABLE would be used interchangeably with
_LIBCPP_ABI_VERSION >= 2. This was confusing and creating unnecessary
complexity.

This patch removes _LIBCPP_ABI_UNSTABLE -- instead, the LIBCXX_ABI_UNSTABLE
CMake option will result in the LIBCXX_ABI_VERSION being set to '2', the
current unstable ABI. As a result, in the code, we only have _LIBCPP_ABI_VERSION
to check in order to query the current ABI version.

As a fly-by, this also defines the ABI namespace during CMake configuration
to reduce complexity in __config. I believe it was previously done this
way because we used to try to use __config_site as seldom as possible.
Now that we always ship a __config_site, it doesn't really matter and
I think being explicit about how the library is configured in the __config_site
is actually a feature.

Differential Revision: https://reviews.llvm.org/D119173

libcxx/CMakeLists.txt

@@ -179,9 +179,17 @@ cmake_dependent_option(LIBCXX_INSTALL_EXPERIMENTAL_LIBRARY
         "Install libc++experimental.a" ON
         "LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY;LIBCXX_INSTALL_LIBRARY" OFF)
 
-set(LIBCXX_ABI_VERSION "1" CACHE STRING "ABI version of libc++. Can be either 1 or 2, where 2 is currently not stable. Defaults to 1.")
-set(LIBCXX_ABI_NAMESPACE "" CACHE STRING "The inline ABI namespace used by libc++. It defaults to __n where `n` is the current ABI version.")
-option(LIBCXX_ABI_UNSTABLE "Unstable ABI of libc++." OFF)
+option(LIBCXX_ABI_UNSTABLE "Use the unstable ABI of libc++. This is equivalent to specifying LIBCXX_ABI_VERSION=n, where n is the not-yet-stable version." OFF)
+if (LIBCXX_ABI_UNSTABLE)
+  set(abi_version "2")
+else()
+  set(abi_version "1")
+endif()
+set(LIBCXX_ABI_VERSION "${abi_version}" CACHE STRING "ABI version of libc++. Can be either 1 or 2, where 2 is currently the unstable ABI. Defaults to 1 unless LIBCXX_ABI_UNSTABLE is specified, in which case this is 2.")
+set(LIBCXX_ABI_NAMESPACE "__${LIBCXX_ABI_VERSION}" CACHE STRING "The inline ABI namespace used by libc++. It defaults to __n where `n` is the current ABI version.")
+if (NOT LIBCXX_ABI_NAMESPACE MATCHES "__.*")
+  message(FATAL_ERROR "LIBCXX_ABI_NAMESPACE must be a reserved identifier.")
+endif()
 option(LIBCXX_ABI_FORCE_ITANIUM "Ignore auto-detection and force use of the Itanium ABI.")
 option(LIBCXX_ABI_FORCE_MICROSOFT "Ignore auto-detection and force use of the Microsoft ABI.")
 
@@ -858,19 +866,8 @@ function(cxx_add_windows_flags target)
 endfunction()
 
 # Configuration file flags =====================================================
-if (NOT LIBCXX_ABI_VERSION EQUAL 1)
-  config_define(${LIBCXX_ABI_VERSION} _LIBCPP_ABI_VERSION)
-endif()
-if (NOT LIBCXX_ABI_NAMESPACE STREQUAL "")
-  if (NOT LIBCXX_ABI_NAMESPACE MATCHES "__.*")
-    message(FATAL_ERROR "LIBCXX_ABI_NAMESPACE must be a reserved identifier.")
-  endif()
-  if (LIBCXX_ABI_NAMESPACE MATCHES "__[0-9]+$")
-    message(FATAL_ERROR "LIBCXX_ABI_NAMESPACE '${LIBCXX_ABI_NAMESPACE}' is reserved for use by libc++.")
-  endif()
-  config_define(${LIBCXX_ABI_NAMESPACE} _LIBCPP_ABI_NAMESPACE)
-endif()
-config_define_if(LIBCXX_ABI_UNSTABLE _LIBCPP_ABI_UNSTABLE)
+config_define(${LIBCXX_ABI_VERSION} _LIBCPP_ABI_VERSION)
+config_define(${LIBCXX_ABI_NAMESPACE} _LIBCPP_ABI_NAMESPACE)
 config_define_if(LIBCXX_ABI_FORCE_ITANIUM _LIBCPP_ABI_FORCE_ITANIUM)
 config_define_if(LIBCXX_ABI_FORCE_MICROSOFT _LIBCPP_ABI_FORCE_MICROSOFT)
 config_define_if(LIBCXX_HIDE_FROM_ABI_PER_TU_BY_DEFAULT _LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT)

libcxx/docs/BuildingLibcxx.rst

@@ -443,10 +443,10 @@ The following options allow building libc++ for a different ABI version.
   with other libc++ versions.
 
   .. warning::
-    When providing a custom namespace, it's the users responsibility to ensure the name won't cause
+    When providing a custom namespace, it's the user's responsibility to ensure the name won't cause
     conflicts with other names defined by libc++, both now and in the future. In particular, inline
-    namespaces of the form ``__[0-9]+`` are strictly reserved by libc++ and may not be used by users.
-    Doing otherwise could cause conflicts and hinder libc++ ABI evolution.
+    namespaces of the form ``__[0-9]+`` could cause conflicts with future versions of the library,
+    and so should be avoided.
 
 .. option:: LIBCXX_ABI_DEFINES:STRING
 

libcxx/docs/ReleaseNotes.rst

@@ -41,6 +41,12 @@ New Features
 API Changes
 -----------
 
+- The ``_LIBCPP_ABI_UNSTABLE`` macro has been removed in favour of setting
+  ``_LIBCPP_ABI_VERSION=2``. This should not have any impact on users because
+  they were not supposed to set ``_LIBCPP_ABI_UNSTABLE`` manually, however we
+  still feel that it is worth mentioning in the release notes in case some users
+  had been doing it.
+
 ABI Changes
 -----------
 

libcxx/include/__config

@@ -26,14 +26,6 @@
 
 #define _LIBCPP_VERSION 15000
 
-#ifdef _LIBCPP_ABI_UNSTABLE
-#  define _LIBCPP_ABI_VERSION 2
-#endif
-
-#ifndef _LIBCPP_ABI_VERSION
-#  define _LIBCPP_ABI_VERSION 1
-#endif
-
 #if __STDC_HOSTED__ == 0
 #  define _LIBCPP_FREESTANDING
 #endif
@@ -150,13 +142,6 @@
 #  define _LIBCPP_ABI_BAD_FUNCTION_CALL_KEY_FUNCTION
 #endif
 
-#define _LIBCPP_CONCAT1(_LIBCPP_X,_LIBCPP_Y) _LIBCPP_X##_LIBCPP_Y
-#define _LIBCPP_CONCAT(_LIBCPP_X,_LIBCPP_Y) _LIBCPP_CONCAT1(_LIBCPP_X,_LIBCPP_Y)
-
-#ifndef _LIBCPP_ABI_NAMESPACE
-# define _LIBCPP_ABI_NAMESPACE _LIBCPP_CONCAT(__,_LIBCPP_ABI_VERSION)
-#endif
-
 #if __cplusplus < 201103L
 #define _LIBCPP_CXX03_LANG
 #endif

libcxx/include/__config_site.in

@@ -10,7 +10,7 @@
 #define _LIBCPP_CONFIG_SITE
 
 #cmakedefine _LIBCPP_ABI_VERSION @_LIBCPP_ABI_VERSION@
-#cmakedefine _LIBCPP_ABI_UNSTABLE
+#cmakedefine _LIBCPP_ABI_NAMESPACE @_LIBCPP_ABI_NAMESPACE@
 #cmakedefine _LIBCPP_ABI_FORCE_ITANIUM
 #cmakedefine _LIBCPP_ABI_FORCE_MICROSOFT
 #cmakedefine _LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT
@@ -25,7 +25,6 @@
 #cmakedefine _LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS
 #cmakedefine _LIBCPP_NO_VCRUNTIME
 #cmakedefine _LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION @_LIBCPP_TYPEINFO_COMPARISON_IMPLEMENTATION@
-#cmakedefine _LIBCPP_ABI_NAMESPACE @_LIBCPP_ABI_NAMESPACE@
 #cmakedefine _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY
 #cmakedefine _LIBCPP_HAS_PARALLEL_ALGORITHMS
 #cmakedefine _LIBCPP_HAS_NO_RANDOM_DEVICE

libcxx/test/libcxx/utilities/utility/pairs/pairs.pair/non_trivial_copy_move_ABI.pass.cpp

@@ -14,14 +14,9 @@
 
 // template <class T1, class T2> struct pair
 
-// Test that we properly provide the trivial copy operations by default.
-
-// FreeBSD provides the old ABI. This test checks the new ABI so we need
-// to manually turn it on.
-#undef _LIBCPP_ABI_UNSTABLE
-#undef _LIBCPP_ABI_VERSION
-#define _LIBCPP_ABI_VERSION 1
-#define _LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR
+// Test that we provide the non-trivial copy operations when _LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR
+// is specified.
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR
 
 #include <utility>
 #include <type_traits>
@@ -31,10 +26,6 @@
 
 #include "test_macros.h"
 
-#if !defined(_LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR)
-#error trivial ctor ABI macro defined
-#endif
-
 template <class T>
 struct HasNonTrivialABI : std::integral_constant<bool,
     !std::is_trivially_destructible<T>::value

libcxx/test/libcxx/utilities/utility/pairs/pairs.pair/trivial_copy_move_ABI.pass.cpp

@@ -12,11 +12,8 @@
 
 // Test that we properly provide the trivial copy operations by default.
 
-// FreeBSD provides the old ABI. This test checks the new ABI so we need
-// to manually turn it on.
-#if defined(__FreeBSD__)
-#define _LIBCPP_ABI_UNSTABLE
-#endif
+// FreeBSD still provides the old ABI for std::pair.
+// XFAIL: freebsd
 
 #include <utility>
 #include <type_traits>
@@ -26,10 +23,6 @@
 
 #include "test_macros.h"
 
-#if defined(_LIBCPP_DEPRECATED_ABI_DISABLE_PAIR_TRIVIAL_COPY_CTOR)
-#error Non-trivial ctor ABI macro defined
-#endif
-
 template <class T>
 struct HasTrivialABI : std::integral_constant<bool,
     std::is_trivially_destructible<T>::value

libcxx/utils/gdb/libcxx/printers.py

@@ -7,8 +7,7 @@
 #===----------------------------------------------------------------------===##
 """GDB pretty-printers for libc++.
 
-These should work for objects compiled when _LIBCPP_ABI_UNSTABLE is defined
-and when it is undefined.
+These should work for objects compiled with either the stable ABI or the unstable ABI.
 """
 
 from __future__ import print_function

libcxx/utils/libcxx/test/features.py

@@ -119,7 +119,6 @@ macros = {
   '_LIBCPP_HAS_THREAD_API_PTHREAD': 'libcpp-has-thread-api-pthread',
   '_LIBCPP_NO_VCRUNTIME': 'libcpp-no-vcruntime',
   '_LIBCPP_ABI_VERSION': 'libcpp-abi-version',
-  '_LIBCPP_ABI_UNSTABLE': 'libcpp-abi-unstable',
   '_LIBCPP_HAS_NO_FILESYSTEM_LIBRARY': 'libcpp-has-no-filesystem-library',
   '_LIBCPP_HAS_NO_RANDOM_DEVICE': 'libcpp-has-no-random-device',
   '_LIBCPP_HAS_NO_LOCALIZATION': 'libcpp-has-no-localization',