[libc++] Use CMAKE_AR for merging static libraries

[mstorsjo]

Summary

Don't prepend the ar commands by a dash, not all ar implementations support that (llvm-ar doesn't).

Also pass the 's' option when creating the merged library, to create an index.

[mstorsjo]

Ping

[compnerd]

If we handle this in CMake, this will be unnecessary.

[mstorsjo]

Ping @EricWF

[EricWF]

Ironically I think parts of this change should be moved into merge_archives.py.

the ar used in merge_archives.py might not be the right one for the target

OK, then we should modify merge_archives.py to support optionally specifying the ar executable.

(and the invocation doesn't include the 's' modifier for updating the archive index)

Isn't this also just a bug in merge_archives.py?

[mstorsjo]

In D37134#868497, @EricWF wrote:

Ironically I think parts of this change should be moved into merge_archives.py.

the ar used in merge_archives.py might not be the right one for the target

OK, then we should modify merge_archives.py to support optionally specifying the ar executable.

(and the invocation doesn't include the 's' modifier for updating the archive index)

Isn't this also just a bug in merge_archives.py?

Hm, indeed, that's probably a better solution. I'll give that a go and see how it goes.

[mstorsjo]

The previous patch actually lacked the 's' option that the summary talked about

[EricWF]

LGTM, minus inline comments.

utils/merge_archives.py

97

-a doesn't feel very descriptive, and unlike -o and -L it isn't used commonly elsewhere. Maybe just the long option on this one?

lib/CMakeLists.txt

else()
       set(MERGE_ARCHIVES_ABI_TARGET
           "${CMAKE_STATIC_LIBRARY_PREFIX}${LIBCXX_CXX_ABI_LIBRARY}${CMAKE_STATIC_LIBRARY_SUFFIX}")
     endif()
     add_custom_command(TARGET cxx_static POST_BUILD
     COMMAND
       ${PYTHON_EXECUTABLE} ${LIBCXX_SOURCE_DIR}/utils/merge_archives.py
     ARGS
       -o $<TARGET_LINKER_FILE:cxx_static>
+      -a "${CMAKE_AR}"
       "$<TARGET_LINKER_FILE:cxx_static>"
       "${MERGE_ARCHIVES_ABI_TARGET}"
       "${MERGE_ARCHIVES_SEARCH_PATHS}"
     WORKING_DIRECTORY ${LIBCXX_BUILD_DIR}
     )
   endif()
 endif()
 

utils/merge_archives.py

parser.add_argument(
         '-o', '--output', dest='output', required=True,
         help='The output file. stdout is used if not given',
         type=str, action='store')
     parser.add_argument(
         '-L', dest='search_paths',
         help='Paths to search for the libraries along', action='append',
         nargs=1)
     parser.add_argument(
+        '-a', '--ar', dest='ar_exe', required=False,
+        help='The ar executable to use, finds \'ar\' in the path if not given',
+        type=str, action='store')
+    parser.add_argument(
         'archives', metavar='archives',  nargs='+',
         help='The archives to merge')
 
     args = parser.parse_args()
 
+    ar_exe = args.ar_exe
+    if not ar_exe:
         ar_exe = distutils.spawn.find_executable('ar')
     if not ar_exe:
         print_and_exit("failed to find 'ar' executable")
 
     if len(args.archives) < 2:
         print_and_exit('fewer than 2 inputs provided')
     archives = [find_and_diagnose_missing(ar, args.search_paths)
                 for ar in args.archives]
     print ('Merging archives: %s' % archives)
     if not os.path.exists(os.path.dirname(args.output)):
         print_and_exit("output path doesn't exist: '%s'" % args.output)
 
     global temp_directory_root
     temp_directory_root = tempfile.mkdtemp('.libcxx.merge.archives')
 
     for arc in archives:
-        execute_command_verbose([ar_exe, '-x', arc], cwd=temp_directory_root,
+        execute_command_verbose([ar_exe, 'x', arc], cwd=temp_directory_root,
                                 verbose=args.verbose)
 
     files = glob.glob(os.path.join(temp_directory_root, '*.o*'))
     if not files:
         print_and_exit('Failed to glob for %s' % glob_path)
-    cmd = [ar_exe, '-qc', args.output] + files
+    cmd = [ar_exe, 'qcs', args.output] + files
     execute_command_verbose(cmd, cwd=temp_directory_root, verbose=args.verbose)
 
 
 if __name__ == '__main__':
     main()
     exit_with_cleanups(0)