[libc++] Remove the __libcpp_version file

[ldionne]

Summary

It seems to have been added back in 761e42fa3dd72 for Clang to use it,
however it seems to have never been used for that purpose, so it is
probably fine to remove it.

[ldionne]

@EricWF I'm curious since you added this -- am I correct when I claim that this ended up not being used by Clang, or did I miss something? Do you think it's fine to remove it?

[EricWF]

@rsmith had plans for this header. Richard, are we good to remove this?

[ldionne]

Gentle ping. I'll ship this tomorrow unless @rsmith provides more information. Richard, I'll also ping you on Discord just in case.

[rsmith]

There was an idea that we could use this to enable / disable version-specific workarounds for libc++/clang incompatibilities (eg, if recent clang sees it's using a sufficiently new version of libc++ then it can avoid enabling a workaround that's only necessary for older versions of libc++). We never implemented the clang side of this, though, so I don't think it's used by anything, and it seems like something we can add back later if there's a motivating use case.

[ldionne]

In D122330#3418061, @rsmith wrote:

There was an idea that we could use this to enable / disable version-specific workarounds for libc++/clang incompatibilities (eg, if recent clang sees it's using a sufficiently new version of libc++ then it can avoid enabling a workaround that's only necessary for older versions of libc++). We never implemented the clang side of this, though, so I don't think it's used by anything, and it seems like something we can add back later if there's a motivating use case.

Got it. Also, things have evolved to a point where libc++ and Clang are generally in rough lockstep with each other, so hopefully this shouldn't be necessary. I agree this can be added later if needed, but thanks for the additional context.

[ldionne]

(I'm going to ship this since you didn't seem opposed to it)

libcxx/docs/Contributing.rst

 guidelines -- if you would like to be added to it, please reach out on Discord.
 
 Post-release check list
 =======================
 
 After branching for an LLVM release:
 
 1. Update ``_LIBCPP_VERSION`` in ``libcxx/include/__config``
-2. Update the ``libcxx/include/__libcpp_version`` file
-3. Update the version number in ``libcxx/docs/conf.py``
-4. Update ``_LIBCPPABI_VERSION`` in ``libcxxabi/include/cxxabi.h``
-5. Update ``_LIBUNWIND_VERSION`` in ``libunwind/include/__libunwind_config.h``
+2. Update the version number in ``libcxx/docs/conf.py``
+3. Update ``_LIBCPPABI_VERSION`` in ``libcxxabi/include/cxxabi.h``
+4. Update ``_LIBUNWIND_VERSION`` in ``libunwind/include/__libunwind_config.h``
 
 Exporting new symbols from the library
 ======================================
 
 When exporting new symbols from libc++, you must update the ABI lists located in ``lib/abi``.
 To test whether the lists are up-to-date, please run the target ``check-cxx-abilist``.
 To regenerate the lists, use the target ``generate-cxx-abilist``.
 The ABI lists must be updated for all supported platforms; currently Linux and

libcxx/include/CMakeLists.txt

set(files
   __iterator/projected.h
   __iterator/readable_traits.h
   __iterator/reverse_access.h
   __iterator/reverse_iterator.h
   __iterator/size.h
   __iterator/sortable.h
   __iterator/unreachable_sentinel.h
   __iterator/wrap_iter.h
-  __libcpp_version
   __locale
   __mbstate_t.h
   __memory/addressof.h
   __memory/allocation_guard.h
   __memory/allocator.h
   __memory/allocator_arg_t.h
   __memory/allocator_traits.h
   __memory/auto_ptr.h

libcxx/include/__libcpp_version

-15000

libcxx/test/libcxx/libcpp_version.pass.cpp

-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-// Test that the __libcpp_version file matches the value of _LIBCPP_VERSION
-
-#include <__config>
-
-#ifndef _LIBCPP_VERSION
-#error _LIBCPP_VERSION must be defined
-#endif
-
-static const int libcpp_version =
-#include <__libcpp_version>
-;
-
-static_assert(_LIBCPP_VERSION == libcpp_version,
-              "_LIBCPP_VERSION doesn't match __libcpp_version");
-
-int main(int, char**) {
-
-
-  return 0;
-}

libcxx/test/libcxx/lint/lint_headers.sh.py

 # RUN: %{python} %s
 
 # Verify that each run of consecutive #include directives
 # in each libcxx/include/ header is maintained in alphabetical order.
 
 import glob
 import os
 import re
 
 
 def exclude_from_consideration(path):
     return (
         path.endswith('.txt') or
         path.endswith('.modulemap') or
         os.path.basename(path) == '__config' or
         os.path.basename(path) == '__config_site.in' or
-        os.path.basename(path) == '__libcpp_version' or
         not os.path.isfile(path)
     )
 
 
 def check_for_pragma_GCC_system_header(pretty_fname, lines):
     if pretty_fname not in ['__undef_macros']:
         if '#  pragma GCC system_header\n' not in lines:
             print('FAILED TO FIND #  pragma GCC system_header in libcxx/include/%s!' % pretty_fname)

libcxx/utils/generate_assertion_tests.py

header_restrictions = {
     "experimental/unordered_map": "__cplusplus >= 201103L",
     "experimental/unordered_set": "__cplusplus >= 201103L",
     "experimental/vector": "__cplusplus >= 201103L",
 }
 
 private_headers_still_public_in_modules = [
     '__assert', '__bsd_locale_defaults.h', '__bsd_locale_fallbacks.h', '__config',
     '__config_site.in', '__debug', '__hash_table',
-    '__libcpp_version', '__threading_support', '__tree', '__undef_macros'
+    '__threading_support', '__tree', '__undef_macros'
 ]
 
 def find_script(file):
     """Finds the script used to generate a file inside the file itself. The script is delimited by
        BEGIN-SCRIPT and END-SCRIPT markers.
     """
     with open(file, 'r') as f:
         content = f.read()

libcxx/utils/generate_private_header_tests.py

def relative_path(path):
     return path.as_posix()[len(include_path + '/'):]
 
 
 def is_still_public(path):
     rp = relative_path(path)
     return not rp.startswith('__support') and rp not in [
         "__assert", "__bsd_locale_defaults.h", "__bsd_locale_fallbacks.h", "__config",
         "__config_site.in", "__debug", "__hash_table",
-        "__libcpp_version", "__threading_support", "__tree", "__undef_macros"
+        "__threading_support", "__tree", "__undef_macros"
     ]
 
 
 def main():
     paths = [
         relative_path(p) for p in Path(include_path).rglob('*')
         if relative_path(p).startswith('__') and not p.is_dir()
         and is_still_public(p)

libcxx/utils/graph_header_deps.py

 #!/usr/bin/env python
 #===----------------------------------------------------------------------===##
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 #
 #===----------------------------------------------------------------------===##
 
 import argparse
 import os
 import re
 import sys
 
 
 def is_config_header(h):
-    return os.path.basename(h) in ['__config', '__libcpp_version', '__undef_macros', 'version']
+    return os.path.basename(h) in ['__config', '__undef_macros', 'version']
 
 
 def is_experimental_header(h):
     return ('experimental/' in h) or ('ext/' in h)
 
 
 def is_support_header(h):
     return '__support/' in h