[libc++] [cmake] Better diagnostics for missing abi library headers

[broadwaylamb]

Summary

The main motivation for this change is this build failure, which for some reason only happens on the buildbot.

This is NFC. We only add additional information to the log.

[ldionne]

LGTM, but in the future I think it would be reasonable to just require libc++ and libc++abi sources when building either one of them. That would simplify a lot of searching logic and we could start sharing stuff between the two. And concretely, I think it wouldn't change much since we're in the monorepo anyway.

@broadwaylamb I think you might have some funky requirements around that -- would it be problematic for you if we required a monorepo checkout when building libc++ or libc++abi?

[broadwaylamb]

In D75991#1917193, @ldionne wrote:

@broadwaylamb I think you might have some funky requirements around that -- would it be problematic for you if we required a monorepo checkout when building libc++ or libc++abi?

Honestly, I didn't know that we still supported non-monorepo checkout. On the buildbots I'm working on, I believe this is a non-issue. I can't speak for everyone, though.

[ldionne]

In D75991#1917248, @broadwaylamb wrote:

In D75991#1917193, @ldionne wrote:

@broadwaylamb I think you might have some funky requirements around that -- would it be problematic for you if we required a monorepo checkout when building libc++ or libc++abi?

Honestly, I didn't know that we still supported non-monorepo checkout. On the buildbots I'm working on, I believe this is a non-issue. I can't speak for everyone, though.

Nice. For some reason I thought you had that requirement, and I didn't want to change it without asking cause it would have broken you. I guess I'll ask on libc++-dev just to be sure.

libcxx/cmake/Modules/HandleLibCXXABI.cmake

set(LIBCXX_CXX_ABI_LIBRARY_PATH "${LIBCXX_CXX_ABI_LIBRARY_PATH}"
     )
   set(LIBCXX_CXX_SHARED_ABI_LIBRARY ${abishared})
   set(LIBCXX_CXX_STATIC_ABI_LIBRARY ${abistatic})
   set(LIBCXX_ABILIB_FILES ${abifiles})
 
   foreach(fpath ${LIBCXX_ABILIB_FILES})
     set(found FALSE)
     foreach(incpath ${LIBCXX_CXX_ABI_INCLUDE_PATHS})
+      message(STATUS "Looking for ${fpath} in ${incpath}")
       if (EXISTS "${incpath}/${fpath}")
         set(found TRUE)
+        message(STATUS "Looking for ${fpath} in ${incpath} - found")
         get_filename_component(dstdir ${fpath} PATH)
         get_filename_component(ifile ${fpath} NAME)
         set(src ${incpath}/${fpath})
 
         set(dst ${LIBCXX_BINARY_INCLUDE_DIR}/${dstdir}/${ifile})
         add_custom_command(OUTPUT ${dst}
             DEPENDS ${src}
             COMMAND ${CMAKE_COMMAND} -E copy_if_different ${src} ${dst}
foreach(incpath ${LIBCXX_CXX_ABI_INCLUDE_PATHS})
 
         if (LIBCXX_INSTALL_HEADERS)
           install(FILES "${LIBCXX_BINARY_INCLUDE_DIR}/${fpath}"
             DESTINATION ${LIBCXX_INSTALL_HEADER_PREFIX}include/c++/v1/${dstdir}
             COMPONENT cxx-headers
             PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
             )
         endif()
+      else()
+        message(STATUS "Looking for ${fpath} in ${incpath} - not found")
       endif()
     endforeach()
     if (NOT found)
-      message(WARNING "Failed to find ${fpath}")
+      message(WARNING "Failed to find ${fpath} in ${LIBCXX_CXX_ABI_INCLUDE_PATHS}")
     endif()
   endforeach()
 
   include_directories("${LIBCXX_BINARY_INCLUDE_DIR}")
   add_custom_target(cxx_abi_headers ALL DEPENDS ${abilib_headers})
   set(LIBCXX_CXX_ABI_HEADER_TARGET "cxx_abi_headers")
 endmacro()