[CMake] Option to control whether shared/static library is installed

[phosek]

Summary

Currently it's only possible to control whether shared or static library build of libc++, libc++abi and libunwind is enabled or disabled and whether to install everything we've built or not. However, it'd be useful to have more fine grained control, e.g. when static libraries are merged together into libc++.a we don't need to install libc++abi.a and libunwind.a. This change adds this option.

[smeenai]

Patch is missing context.

[smeenai]

Also, this ended up going to llvm-commits instead of cfe-commits, which isn't ideal.

[ldionne]

I don't like the fact that we're adding options like crazy, thus making the build more complicated. If you don't want to have some libraries that were built, why not just remove them afterwards?

[phosek]

In D49573#1169615, @ldionne wrote:

I don't like the fact that we're adding options like crazy, thus making the build more complicated. If you don't want to have some libraries that were built, why not just remove them afterwards?

The motivation behind this is that you could produce a complete toolchain with just CMake, combined with the fact that the cache files are all part of the LLVM tree, anyone can build the toolchain themselves which is useful when reproducing issues. We would like to add Fuchsia bots to upstream in the near future where reproducibility is going to be even more important and I'd like to avoid for people to have to run additional post-processing scripts.

Regarding this change, this in combination with D49502 is all we need to exactly what gets built and installed, I don't plan on adding anymore options. Alternative that I also considered would be avoid exposing these options and instead do this implicitly based on the variables that are being set, e.g. in libc++abi build check if LIBCXX_STATICALLY_LINK_ABI_IN_STATIC_LIBRARY is set and if so don't even install libc++abi.a. The problem is that while this may work for us, I'm pretty sure there are going to be other clients that have other requirements where this is not the right choice and we could see combinatorial explosion of different configurations, so providing these options is probably a better choice.

[ldionne]

Can't you simply set LIBCXX_ENABLE_SHARED=OFF when you don't want to build/install the shared library and LIBCXX_ENABLE_STATIC=OFF for the static library?

[phosek]

You're right that we don't need these flags for libc++, we only need them for libc++abi and libunwind for the cases when one of these is linked into libc++ or libc++abi respectively. I added them for consistency, but I'm fine dropping them from libc++, would that be more acceptable?

[ldionne]

Ah, so you mean you need it for libc++abi because you want to build them but not install them (so they're linked into libc++)? Then LGTM as-is. I'd like to see what Eric has to say though.

[sbc100]

FYI, this broke the WebAssembly waterfall, where the library is no longer being installed: https://wasm-stat.us/builders/linux/builds/34191

There is probably an easy fix, but I thought I'd post here for the record.

[sbc100]

https://reviews.llvm.org/D49825 seems to fix it.

CMakeLists.txt

if (LIBCXX_BENCHMARK_NATIVE_STDLIB)
   endif()
 endif()
 
 option(LIBCXX_INCLUDE_DOCS "Build the libc++ documentation." ${LLVM_INCLUDE_DOCS})
 set(LIBCXX_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}" CACHE STRING
     "Define suffix of library directory name (32/64)")
 option(LIBCXX_INSTALL_HEADERS "Install the libc++ headers." ON)
 option(LIBCXX_INSTALL_LIBRARY "Install the libc++ library." ON)
+cmake_dependent_option(LIBCXX_INSTALL_STATIC_LIBRARY
+  "Install the static libc++ library." ON
+  "LIBCXX_ENABLE_STATIC;LIBCXX_INSTALL_LIBRARY" OFF)
+cmake_dependent_option(LIBCXX_INSTALL_SHARED_LIBRARY
+  "Install the shared libc++ library." ON
+  "LIBCXX_ENABLE_SHARED;LIBCXX_INSTALL_LIBRARY" OFF)
 option(LIBCXX_INSTALL_SUPPORT_HEADERS "Install libc++ support headers." ON)
 cmake_dependent_option(LIBCXX_INSTALL_EXPERIMENTAL_LIBRARY
         "Install libc++experimental.a" ON
         "LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY;LIBCXX_INSTALL_LIBRARY" OFF)
 if (FUCHSIA)
   set(DEFAULT_ABI_VERSION 2)
 else()
   set(DEFAULT_ABI_VERSION 1)

lib/CMakeLists.txt

target_compile_definitions(cxx_objects
                                _CRT_STDIO_ISO_WIDE_SPECIFIERS)
 endif()
 
 set_target_properties(cxx_objects
   PROPERTIES
     COMPILE_FLAGS "${LIBCXX_COMPILE_FLAGS}"
 )
 
-set(LIBCXX_TARGETS)
-
 # Build the shared library.
 if (LIBCXX_ENABLE_SHARED)
   add_library(cxx_shared SHARED $<TARGET_OBJECTS:cxx_objects>)
   if(COMMAND llvm_setup_rpath)
     llvm_setup_rpath(cxx_shared)
   endif()
   target_link_libraries(cxx_shared ${LIBCXX_LIBRARIES})
   set_target_properties(cxx_shared
     PROPERTIES
       LINK_FLAGS    "${LIBCXX_LINK_FLAGS}"
       OUTPUT_NAME   "c++"
       VERSION       "${LIBCXX_ABI_VERSION}.0"
       SOVERSION     "${LIBCXX_ABI_VERSION}"
   )
-  list(APPEND LIBCXX_TARGETS "cxx_shared")
+  list(APPEND LIBCXX_BUILD_TARGETS "cxx_shared")
+  if (LIBCXX_INSTALL_SHARED_LIBRARY)
+    list(APPEND LIBCXX_INSTALL_TARGETS "cxx_shared")
+  endif()
   if(WIN32 AND NOT MINGW AND NOT "${CMAKE_HOST_SYSTEM_NAME}" STREQUAL "Windows")
     # Since we most likely do not have a mt.exe replacement, disable the
     # manifest bundling.  This allows a normal cmake invocation to pass which
     # will attempt to use the manifest tool to generate the bundled manifest
     set_target_properties(cxx_shared PROPERTIES
                           APPEND_STRING PROPERTY LINK_FLAGS " /MANIFEST:NO")
   endif()
 endif()
 
 # Build the static library.
 if (LIBCXX_ENABLE_STATIC)
   add_library(cxx_static STATIC $<TARGET_OBJECTS:cxx_objects>)
   target_link_libraries(cxx_static ${LIBCXX_LIBRARIES})
   set(CMAKE_STATIC_LIBRARY_PREFIX "lib")
   set_target_properties(cxx_static
     PROPERTIES
       LINK_FLAGS    "${LIBCXX_LINK_FLAGS}"
       OUTPUT_NAME   "c++"
   )
-
-  list(APPEND LIBCXX_TARGETS "cxx_static")
+  list(APPEND LIBCXX_BUILD_TARGETS "cxx_static")
+  if (LIBCXX_INSTALL_STATIC_LIBRARY)
+    list(APPEND LIBCXX_INSTALL_TARGETS "cxx_static")
+  endif()
   # Attempt to merge the libc++.a archive and the ABI library archive into one.
   if (LIBCXX_STATICALLY_LINK_ABI_IN_STATIC_LIBRARY)
     set(MERGE_ARCHIVES_SEARCH_PATHS "")
     if (LIBCXX_CXX_ABI_LIBRARY_PATH)
       set(MERGE_ARCHIVES_SEARCH_PATHS "-L${LIBCXX_CXX_ABI_LIBRARY_PATH}")
     endif()
     if ((TARGET ${LIBCXX_CXX_ABI_LIBRARY}) OR
         (${LIBCXX_CXX_ABI_LIBRARY} MATCHES "cxxabi(_static|_shared)?" AND HAVE_LIBCXXABI))
ARGS
       "${MERGE_ARCHIVES_ABI_TARGET}"
       "${MERGE_ARCHIVES_SEARCH_PATHS}"
     WORKING_DIRECTORY ${LIBCXX_BUILD_DIR}
     )
   endif()
 endif()
 
 # Add a meta-target for both libraries.
-add_custom_target(cxx DEPENDS cxx-headers ${LIBCXX_TARGETS})
+add_custom_target(cxx DEPENDS cxx-headers ${LIBCXX_BUILD_TARGETS})
 
 if (LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY)
   file(GLOB LIBCXX_EXPERIMENTAL_SOURCES ../src/experimental/*.cpp)
   if (LIBCXX_ENABLE_FILESYSTEM)
     file(GLOB LIBCXX_FILESYSTEM_SOURCES ../src/experimental/filesystem/*.cpp)
   endif()
   add_library(cxx_experimental STATIC ${LIBCXX_EXPERIMENTAL_SOURCES} ${LIBCXX_FILESYSTEM_SOURCES})
   if (LIBCXX_ENABLE_SHARED)
add_custom_command(TARGET cxx_shared POST_BUILD
     WORKING_DIRECTORY ${LIBCXX_BUILD_DIR}
   )
 endif()
 
 if (LIBCXX_INSTALL_LIBRARY)
   if (LIBCXX_INSTALL_EXPERIMENTAL_LIBRARY)
     set(experimental_lib cxx_experimental)
   endif()
-  install(TARGETS ${LIBCXX_TARGETS} ${experimental_lib}
+  install(TARGETS ${LIBCXX_INSTALL_TARGETS} ${experimental_lib}
     LIBRARY DESTINATION ${LIBCXX_INSTALL_PREFIX}lib${LIBCXX_LIBDIR_SUFFIX} COMPONENT cxx
     ARCHIVE DESTINATION ${LIBCXX_INSTALL_PREFIX}lib${LIBCXX_LIBDIR_SUFFIX} COMPONENT cxx
     )
   # NOTE: This install command must go after the cxx install command otherwise
   # it will not be executed after the library symlinks are installed.
   if (LIBCXX_ENABLE_SHARED AND LIBCXX_ENABLE_ABI_LINKER_SCRIPT)
     # Replace the libc++ filename with $<TARGET_LINKER_FILE:cxx>
     # after we required CMake 3.0.