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[C++] Building Arrow via FetchContent can fail with versions older than CMake 3.30 #53995

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[C++] Building Arrow via FetchContent can fail with versions older than CMake 3.30#53995
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Component: C++Type: bug

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@raulcd
raulcd
opened on Oct 16, 2026

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

As seen on the iceberg-cpp report here:

Building Arrow via FetchContent on iceberg with older CMake fails. This is because:

For older versions of CMake the variable arrow_SOURCE_DIR is overriden by FetchContent's one because project(arrow) sets it as a cache variable while FetchContent sets a normal variable with precedence. Arrow can't find thirdparty/versions.txt because it is pointing to the tarball root instead of the cpp subfolder. See policy https://cmake.org/cmake/help/latest/policy/CMP0180.html
We should fix upstream Arrow so it does not rely on arrow_SOURCE_DIR to allow older CMake builds.

See the PR I did here with the patch:

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  1. raulcd
    added
    Type: bug
    on Oct 16, 2026
  2. github-actions
    added
    Component: C++
    on Oct 16, 2026

  3. raulcd commented on Oct 16, 2026

    @raulcd
    raulcd
    on Oct 16, 2026
    MemberAuthor

    @kou what do you think about this, the patch I apply there seems to fix the issues:

    --- a/cpp/cmake_modules/ThirdpartyToolchain.cmake
+++ b/cpp/cmake_modules/ThirdpartyToolchain.cmake
@@ -365,7 +365,7 @@
 # ----------------------------------------------------------------------
 # Thirdparty versions, environment variables, source URLs

-set(THIRDPARTY_DIR "${arrow_SOURCE_DIR}/thirdparty")
+set(THIRDPARTY_DIR "${ARROW_SOURCE_DIR}/thirdparty")

 add_library(arrow::flatbuffers INTERFACE IMPORTED)
 target_include_directories(arrow::flatbuffers

  4. kou commented on Oct 16, 2026

    @kou
    kou
    on Oct 16, 2026
    Member

    +1

    Let's apply the change in apache/arrow too.

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