Fix CMake configuration error in snappy

[PragmaTwice]

This closes #792.

[PragmaTwice]

@torwig @aleksraiden Hi, could you guys help me to check whether this PR really fixed the CMake error on Fedora or Debian? So thanks!

Here is a simple script for reference to check it:

git clone -b fix-792 https://github.com/PragmaTwice/incubator-kvrocks
cd incubator-kvrocks && ./x.py build

[tisonkun]

May you describe a bit how adding these two files helps resolve the issue?

I think it's about CMake resolving order while it looks like we always set GFLAGS_FOUND & GTEST_FOUND to false.

[PragmaTwice]

May you describe a bit how adding these two files helps resolve the issue?

I think it's about CMake resolving order while it looks like we always set GFLAGS_FOUND & GTEST_FOUND to false.

By default, for find_package(X), CMake will use the builtin FindX.cmake file (provided by CMake) to find the X package.
It will try to find the package in system, e.g. packages installed from package manager.
We overwrite this file to make sure CMake does not use some builtin logic to find the package, because we do not need these package in snappy.

It is actually a bug in (old version of) snappy, we defined SNAPPY_BUILD_TESTS=OFF, but snappy will always find gtest regardless of our provided option, and we do not need gtest in snappy since we do not build unit tests of snappy.

@tisonkun

[tisonkun]

Thanks for your explanation! Sounds good to me.

Although, I don't have a Fedora env to verify it :P

[torwig]

@tisonkun I can confirm that the build process goes smoothly on Fedora 35 now.

[tisonkun]

@torwig Thanks for your confirmation!

Merging...

[aleksraiden]

@tisonkun I can confirm too, that the build process on Debian 11 are OK.