[CI][Conan] Unhandled TypeError in conanfile.py when ARROW_HOME is unset

[PythonicVarun]

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

I encountered a potential unhandled TypeError in ci/conan/all/conanfile.py within the source() method.

Location:
https://github.com/apache/arrow/blob/main/ci/conan/all/conanfile.py#L290-L302

The Issue:
The logic block handling local source copying (when the version is not found in conan_data), the script retrieves ARROW_HOME from the environment:

top_level = os.environ.get("ARROW_HOME")
shutil.copytree(os.path.join(top_level, "cpp"),
                os.path.join(self.source_folder, "cpp"))
shutil.copytree(os.path.join(top_level, "format"),
                os.path.join(self.source_folder, "format"))

If the ARROW_HOME environment variable is not set, os.environ.get returns None. Consequently, passing None to os.path.join raises a TypeError (i.e., TypeError: expected str, bytes or os.PathLike object, not NoneType) rather than a descriptive error message indicating the missing configuration.

Expected Behavior: If ARROW_HOME is required for this build path but is missing, the script should explicitly check for None and raise a clear ConanException (like, "ARROW_HOME environment variable is required but not set") to improve the developer experience.

Proposal: I am happy to submit a PR to add a check for top_level is None and raise a proper exception. Please let me know if this is a desired improvement.

Component(s)

Continuous Integration, Packaging

[raulcd]

Thanks for opening the issue. This is only expected to be used as part of our conan-minimum and conan-maximum CI jobs and those jobs have been failing for several weeks now, see:

• [CI][Packaging] conan-minimum and conan-maximum jobs are failing #48766

The current discussions are about dropping those jobs and with them we would drop the conanfile.py too.

Where you manually using the conanfile.py or where you working with the CI scripts just to understand if there's a use case we are not aware.

[PythonicVarun]

Thanks for the context.

To answer your question: I was not using this file for a manual build. I was simply auditing the CI scripts to understand the project's infrastructure better and spotted this potential unhandled exception.

Since you are considering dropping these jobs and the file entirely, this fix is likely unnecessary. I am happy to close this issue now. If you decide to keep the file and want this patched in the interim, just let me know and I will open the PR.