Gang Wu created ORC-2235:
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Summary: [C++] Preserve CMAKE_MODULE_PATH when dependency
discovery fails
Key: ORC-2235
URL: https://issues.apache.org/jira/browse/ORC-2235
Project: ORC
Issue Type: Bug
Components: C++, build
Affects Versions: 3.0.0, 2.3.1
Reporter: Gang Wu
Fix For: 3.0.0
h2. Problem
The installed C++ {{orcConfig.cmake}} saves {{CMAKE_MODULE_PATH}}, replaces it
with ORC's CMake package directory, discovers its system dependencies with
{{find_dependency()}}, and then restores the original path.
When a dependency cannot be found, {{find_dependency()}} sets {{orc_FOUND}} to
false and calls {{return()}}. This exits the config file before the restoration
code runs, leaking ORC's module path into the consuming project.
This was observed downstream in Apache Arrow: ORC's {{LZ4Alt}} dependency
discovery failed, Arrow fell back to another ORC discovery path, and a later
AWS dependency lookup failed because Arrow's {{FindAWSSDKAlt.cmake}} was no
longer on {{CMAKE_MODULE_PATH}}. The AWS error was a secondary symptom, not
necessarily a missing AWS SDK.
h2. Reproduction
With an installed ORC package whose system dependency cannot be found:
{code:cmake}
set(CMAKE_MODULE_PATH "/consumer/cmake_modules")
find_package(orc CONFIG QUIET)
# orc_FOUND is false, but CMAKE_MODULE_PATH now points to ORC's package
directory.
{code}
The problem is also reproducible from the current main-branch config template
(32046606774da481182dce2956f336dc8e79a579) with a mock missing dependency.
h2. Proposed fix
Isolate dependency discovery in a CMake variable scope using {{block(SCOPE_FOR
VARIABLES PROPAGATE orc_FOUND orc_NOT_FOUND_MESSAGE)}}. This restores the
caller's variables even when {{find_dependency()}} returns early, while
preserving the package failure state and imported dependency targets.
Add configure-only regression tests for successful and unsuccessful dependency
discovery, with {{CMAKE_MODULE_PATH}} initially undefined, empty, or containing
multiple directories.
The separate issue of selecting LZ4 from Homebrew versus Conda is outside the
scope of this fix.
h2. References
* Arrow workaround: https://github.com/apache/arrow/pull/55415
* Downstream report: https://github.com/apache/arrow/issues/55357
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