[C++] Explicitly providing CMAKE_LIBTOOL does not work on MacOS

[jabraham17]

Describe the bug, including details regarding any error messages, version, and platform.

I found that when explicitly specifying -DCMAKE_LIBTOOL=/usr/bin/libtool on MacOS the build fails with

cmake_modules/BuildUtils.cmake:123 (message):
CMAKE_LIBTOOL does not appear to be Apple's libtool: /usr/bin/libtool

libtool -V output: Apple Inc. version cctools_ld-1266.8
Call Stack (most recent call first):
src/arrow/CMakeLists.txt:1047 (arrow_create_merged_static_lib)

I think this is an issue with validate_apple_libtool in cpp/cmake_modules/BuildUtils.cmake, where result_var is not set to true if the version does match

Changing the function to the following seems to work for me (adding the else branch)

    function(validate_apple_libtool result_var item)
      get_libtool_version("${item}" libtool_version)
      if(NOT "${libtool_version}" MATCHES ".*cctools.+([0-9.]+).*")
        set(${result_var}
            FALSE
            PARENT_SCOPE)
      else()
        set(${result_var}
            TRUE
            PARENT_SCOPE)
      endif()
    endfunction()

Component(s)

C++

[raulcd]

Thanks for reporting this!
We have several CI jobs that test with macOS. Could you share a little bit more about your specific setup, how are you building? which macOS version/architecture are you using?

[jabraham17]

I was building with the 24.0.0 release. M1 Mac with MacOS 26.4.1, libtool version Apple Inc. version cctools_ld-1266.8.

I suspect the CI runners don't catch this because they don't explicitly specify -DCMAKE_LIBTOOL when configuring with cmake. If I don't specify -DCMAKE_LIBTOOL=/usr/bin/libtool, then the proper libtool is found and no validation error occurs. If I do specify CMAKE_LIBTOOL, then the validation logic fails.

I'm no cmake expert, but as far as I can tell its the same validation function being called in both codepaths. So I'm not totally sure why its different? Not sure what the semantics of the VALIDATOR function are exactly

[kou]

Could you try GH-49975?

[jabraham17]

yes, patching the 24.0.0 release with that change fixes the issue

[kou]

Thanks for checking this. I'll merge the PR.

[kou]

Issue resolved by pull request 49975
#49975