Fix CMake modules for finding external libraries

[lahwaacz]

What changes were proposed in this pull request?

• allow finding header files in default paths - this is consistent with the logic for finding the library files
• replace undefined variables ${SNAPPY_LIB_NAME} and ${LZ4_LIB_NAME} with the actual names

Why are the changes needed?

The CMake modules are broken. Building anything that depends on orc using cmake (e.g. Apache Arrow) does not work.

How was this patch tested?

Better than the original files 😏

Was this patch authored or co-authored using generative AI tooling?

No

[dongjoon-hyun]

cc @wgtmac

[wgtmac]

Thanks for creating this PR!

The CMake modules are broken. Building anything that depends on orc using cmake (e.g. Apache Arrow) does not work.

Could you elaborate this? I was thinking to remove these obsolete FindXXX.cmake files to use config mode of find_package so we don't have to maintain them.

[lahwaacz]

Could you elaborate this?

Try to build the latest orc version and then arrow using the following cmake options (notice especially -DARROW_DEPENDENCY_SOURCE=SYSTEM and -DARROW_ORC=ON)

https://gitlab.archlinux.org/archlinux/packaging/packages/arrow/-/blob/main/PKGBUILD?ref_type=heads#L80-120

I was thinking to remove these obsolete FindXXX.cmake files to use config mode of find_package so we don't have to maintain them.

The "config mode" is still looking for some .cmake file provided by the library you are finding. Many packages do that, including protobuf, snappy, and zstd, but some don't (e.g. lz4, zlib). But cmake also has its standard FindZLIB module so you don't have to reimplement your own.

[wgtmac]

I think lz4 and zlib have exported their packages to be used by config mode:

• https://github.com/lz4/lz4/blob/dev/build/cmake/lz4Config.cmake.in
• https://github.com/madler/zlib/blob/develop/CMakeLists.txt#L240

[lahwaacz]

• https://github.com/lz4/lz4/blob/dev/build/cmake/lz4Config.cmake.in

But if you install lz4 using a different build system (e.g. Arch Linux uses meson), the CMake integration files are not installed.