[libcxxabi] Unbreak `LLVM_ENABLE_RUNTIMES=libcxxabi` build v2

[Ericson2314]

Summary

New version of D132298.

There is no more fragile IN_LIST. CMake code dealing with libc++ is
pulled out into a (libcxxabi-only) HandleLibCXX module.

I tested this with my distro packaging, replacing D132298. It moves more
code around, but does less because with -DLIBCXXABI_INCLUDE_TESTS=OFF
I don't need to worry about LIBCXXABI_TEST_DEPS containing the other
libraries.

[phosek]

libcxxabi/CMakeLists.txt

75

This option is defined after the include(HandleLibCXX) statement but you use its value inside HandleLibCXX.cmake, isn't that always going to evaluate as falsy?

[Ericson2314]

Fix bugs

[Ericson2314]

libcxxabi/CMakeLists.txt

75

Oops good point. I was setting that manually so didn't catch.

libcxxabi/cmake/Modules/HandleLibCXX.cmake

5–7

My TARGET cxx-headers trick didn't work because that target isn't defined until afterwords, since libcxx mostly depends on`libcxxabi`.

[phosek]

libcxxabi/cmake/Modules/HandleLibCXX.cmake

5–7

Could we use LIBCXXABI_LIBCXX_INCLUDE instead of introducing another option? That is, if LIBCXXABI_LIBCXX_INCLUDE is not empty, it implies using prebuilt libc++ headers.

[Ericson2314]

libcxxabi/cmake/Modules/HandleLibCXX.cmake

5–7

I suppose so, should we rename it something like LIBCXXABI_LIBCXX_INCLUDE_PREBUILT if so?

Per the TODO deprecated libcxxabi/test/lit.site.cfg.in uses this variable and I am not sure why. So that gave me some trepidation about changing things more.

[phosek]

libcxxabi/cmake/Modules/HandleLibCXX.cmake

5–7

How about something like LIBCXXABI_EXTERNAL_LIBCXX_INCLUDES?

[ldionne]

Taking a step back, is there a reason why we don't simply require libcxx from being in LLVM_ENABLE_RUNTIMES when libcxxabi is in it? After all, libcxxabi has always been an implementation detail of libc++, and while it makes sense to use libc++ without libc++abi, the reverse doesn't make sense.

In other words, I question the use case of passing LLVM_ENABLE_RUNTIMES=libcxxabi without libcxx. Can you expand on this?

libcxxabi/cmake/Modules/HandleLibCXX.cmake

2–3

This should not be customizeable. We're in the monorepo, so we can hardcode the path of libc++ from libc++abi.

5–7

Per the TODO deprecated libcxxabi/test/lit.site.cfg.in

Is that still relevant? I can't find it anymore.

6

libcxxabi/CMakeLists.txt

list(INSERT CMAKE_MODULE_PATH 0
   "${LLVM_COMMON_CMAKE_UTILS}"
   "${LLVM_COMMON_CMAKE_UTILS}/Modules"
   )
 
 set(CMAKE_FOLDER "libc++")
 
 set(LIBCXXABI_SOURCE_DIR  ${CMAKE_CURRENT_SOURCE_DIR})
 set(LIBCXXABI_BINARY_DIR  ${CMAKE_CURRENT_BINARY_DIR})
-set(LIBCXXABI_LIBCXX_PATH "${CMAKE_CURRENT_LIST_DIR}/../libcxx" CACHE PATH
-        "Specify path to libc++ source.")
 
 include(GNUInstallDirs)
 
 # Require out of source build.
 include(MacroEnsureOutOfSourceBuild)
 MACRO_ENSURE_OUT_OF_SOURCE_BUILD(
  "${PROJECT_NAME} requires an out of source build. Please create a separate
  build directory and run 'cmake /path/to/${PROJECT_NAME} [options]' there."
  )
 
 #===============================================================================
 # Setup CMake Options
 #===============================================================================
 include(CMakeDependentOption)
 include(HandleCompilerRT)
+include(HandleLibCXX)
 
 # Define options.
 option(LIBCXXABI_ENABLE_EXCEPTIONS
   "Provide support for exceptions in the runtime.
   When disabled, libc++abi does not support stack unwinding and other exceptions-related features." ON)
 option(LIBCXXABI_ENABLE_ASSERTIONS "Enable assertions independent of build mode." ON)
 option(LIBCXXABI_ENABLE_PEDANTIC "Compile with pedantic enabled." ON)
 option(LIBCXXABI_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
option(LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS
   "Build libc++abi with definitions for operator new/delete. These are normally
    defined in libc++abi, but it is also possible to define them in libc++, in
    which case the definition in libc++abi should be turned off." ON)
 option(LIBCXXABI_BUILD_32_BITS "Build 32 bit multilib libc++abi. This option is not supported anymore when building the runtimes. Please specify a full triple instead." ${LLVM_BUILD_32_BITS})
 if (LIBCXXABI_BUILD_32_BITS)
   message(FATAL_ERROR "LIBCXXABI_BUILD_32_BITS is not supported anymore when building the runtimes, please specify a full triple instead.")
 endif()
 
 option(LIBCXXABI_INCLUDE_TESTS "Generate build targets for the libc++abi unit tests." ${LLVM_INCLUDE_TESTS})
 set(LIBCXXABI_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}" CACHE STRING
     "Define suffix of library directory name (32/64)")
 option(LIBCXXABI_INSTALL_HEADERS "Install the libc++abi headers." ON)
 option(LIBCXXABI_INSTALL_LIBRARY "Install the libc++abi library." ON)
 
 set(LIBCXXABI_INSTALL_INCLUDE_DIR "${CMAKE_INSTALL_INCLUDEDIR}/c++/v1" CACHE PATH "Path to install the libc++abi headers at.")
 
 if(LLVM_LIBRARY_OUTPUT_INTDIR)
   set(LIBCXXABI_GENERATED_INCLUDE_DIR "${LLVM_BINARY_DIR}/include/c++/v1")
 else()
   set(LIBCXXABI_GENERATED_INCLUDE_DIR "${CMAKE_BINARY_DIR}/include/c++/v1")
 endif()
 
 # TODO: Remove this after branching for LLVM 15
 if(LIBCXXABI_SYSROOT OR LIBCXXABI_TARGET_TRIPLE OR LIBCXXABI_GCC_TOOLCHAIN)
   message(WARNING "LIBCXXABI_SYSROOT, LIBCXXABI_TARGET_TRIPLE and LIBCXXABI_GCC_TOOLCHAIN are not supported anymore, please use the native CMake equivalents instead")
 endif()
 
-set(LIBCXXABI_LIBCXX_LIBRARY_PATH "" CACHE PATH "The path to libc++ library.")
 set(LIBCXXABI_LIBRARY_VERSION "1.0" CACHE STRING
 "Version of libc++abi. This will be reflected in the name of the shared \
 library produced. For example, -DLIBCXXABI_LIBRARY_VERSION=x.y will \
 result in the library being named libc++abi.x.y.dylib, along with the \
 usual symlinks pointing to that.")
 
 # Default to building a shared library so that the default options still test
 # the libc++abi that is being built. The problem with testing a static libc++abi

 option(LIBCXXABI_SILENT_TERMINATE "Set this to make the terminate handler default to a silent alternative" OFF)
 option(LIBCXXABI_NON_DEMANGLING_TERMINATE "Set this to make the terminate handler
 avoid demangling" OFF)
 
 if (NOT LIBCXXABI_ENABLE_SHARED AND NOT LIBCXXABI_ENABLE_STATIC)
   message(FATAL_ERROR "libc++abi must be built as either a shared or static library.")
 endif()
 
-# TODO: Remove this, which shouldn't be necessary since we know we're being built
-#       side-by-side with libc++.
-set(LIBCXXABI_LIBCXX_INCLUDES "" CACHE PATH
-    "Specify path to libc++ includes.")
-
 set(LIBCXXABI_HERMETIC_STATIC_LIBRARY_DEFAULT OFF)
 if (WIN32)
   set(LIBCXXABI_HERMETIC_STATIC_LIBRARY_DEFAULT ON)
 endif()
 option(LIBCXXABI_HERMETIC_STATIC_LIBRARY
   "Do not export any symbols from the static library." ${LIBCXXABI_HERMETIC_STATIC_LIBRARY_DEFAULT})
 
 if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
else()
   set(LIBCXXABI_INSTALL_LIBRARY_DIR lib${LIBCXXABI_LIBDIR_SUFFIX} CACHE PATH
       "Path where built libc++abi libraries should be installed.")
 endif()
 
 set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${LIBCXXABI_LIBRARY_DIR})
 set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${LIBCXXABI_LIBRARY_DIR})
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${LIBCXXABI_LIBRARY_DIR})
 
-# By default, libcxx and libcxxabi share a library directory.
-if (NOT LIBCXXABI_LIBCXX_LIBRARY_PATH)
-  set(LIBCXXABI_LIBCXX_LIBRARY_PATH "${LIBCXXABI_LIBRARY_DIR}" CACHE PATH
-      "The path to libc++ library." FORCE)
-endif()
-
 # Declare libc++abi configuration variables.
 # They are intended for use as follows:
 # LIBCXXABI_C_FLAGS: General flags for both the c++ compiler and linker.
 # LIBCXXABI_CXX_FLAGS: General flags for both the c++ compiler and linker.
 # LIBCXXABI_COMPILE_FLAGS: Compile only flags.
 # LIBCXXABI_LINK_FLAGS: Linker only flags.
 # LIBCXXABI_LIBRARIES: libraries libc++abi is linked to.
 

libcxxabi/cmake/Modules/HandleLibCXX.cmake

+set(LIBCXXABI_LIBCXX_PATH "${LIBCXXABI_SOURCE_DIR}/../libcxx" CACHE PATH
+    "Specify path to libc++ source.")
+
+# TODO: Move this under the conditional. All usages should use `cxx-headers`
+# instead of this, so this is us used to make the "fake" cxx-headers below and
+# nothing else.
+set(LIBCXXABI_LIBCXX_INCLUDES "" CACHE PATH
+    "Specify path to libc++ includes.")
+if (NOT TARGET cxx-headers)
+  if (NOT IS_DIRECTORY ${LIBCXXABI_LIBCXX_INCLUDES})
+    message(FATAL_ERROR
+      "LIBCXXABI_LIBCXX_INCLUDES=${LIBCXXABI_LIBCXX_INCLUDES} is not a valid directory. "
+      "Since we are not also building libc++, "
+      "please provide the path to where the libc++ headers have been installed.")
+
+  endif()
+  add_library(cxx-headers INTERFACE)
+  target_include_directories(cxx-headers INTERFACE "${LIBCXXABI_LIBCXX_INCLUDES}")
+endif()
+
+if (LIBCXXABI_INCLUDE_TESTS)
+  # The libraries are just needed for the "lit tests"
+
+  # By default, libcxx and libcxxabi share a library directory.
+  set(LIBCXXABI_LIBCXX_LIBRARY_PATH "${LIBCXXABI_LIBRARY_DIR}" CACHE PATH
+      "The path to libc++ library.")
+endif()