[raulcd]

Rationale for this change

When a dependency is not found on ORC its find_dependency returns without resetting previous CMAKE_MODULE_PATH:
https://github.com/apache/orc/blob/32046606774da481182dce2956f336dc8e79a579/c%2B%2B/orcConfig.cmake.in#L45-L55

What changes are included in this PR?

Maintain our CMAKE_MODULE_PATH before calling ORC.

Are these changes tested?

Not on our CI but this has been tested on downstream arrow-cpp-feedstock here:
conda-forge/arrow-cpp-feedstock#2100

Are there any user-facing changes?

No

Was AI used for this PR?

In accordance to the AI generation guidelines, please disclose below whether and how AI was used in this PR.

PR code and description written by:

• Human
• AI

Reviewed before submission by:

• Human
• AI
• Not reviewed

• GitHub Issue: [C++] AWS SDK not found for osx-arm #55357

[github-actions]

⚠️ GitHub issue #55357 has been automatically assigned in GitHub to PR creator.

[Copilot]

🟢 Approval recommended

No active review issues are reported for the change preserving Arrow’s CMake module search path during ORC discovery.

No open issues 🎉

What changed in this PR

Preserves Arrow’s CMake module search path when ORC dependency discovery fails, preventing later lookups such as AWS SDK discovery from losing access to Arrow’s find modules.

Changes:

• Saves and restores CMAKE_MODULE_PATH around find_package(orc), then removes the temporary variable.
• Documents why ORC’s early return requires this workaround.

File	Description
cpp/​cmake_modules/​FindorcAlt.cmake	Preserves the module search path across ORC discovery.

_{Review effort: Balanced}

[h-vetinari]

Thanks a lot for debugging this. I think this is good as an intermediate fix; better would be for orc to fix this for itself.