[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 ↗

(On Diff #114908)

-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

if (LIBCXX_ENABLE_STATIC_ABI_LIBRARY)
     add_custom_command(TARGET cxx_static POST_BUILD
     COMMAND
       ${PYTHON_EXECUTABLE} ${LIBCXX_SOURCE_DIR}/utils/merge_archives.py
     ARGS
       -o $<TARGET_LINKER_FILE:cxx_static>
       "$<TARGET_LINKER_FILE:cxx_static>"
       "${MERGE_ARCHIVES_ABI_TARGET}"
       "${MERGE_ARCHIVES_SEARCH_PATHS}"
+    COMMAND
+      ${CMAKE_RANLIB} $<TARGET_LINKER_FILE:cxx_static>
     WORKING_DIRECTORY ${LIBCXX_BUILD_DIR}
     )
   endif()
 endif()
 
 # Add a meta-target for both libraries.
 add_custom_target(cxx DEPENDS ${LIBCXX_TARGETS})