Use system glslang

[psi29a]

Description

Allow support of using system's glslang if available, otherwise fallback to original git based gslang method.

Fixes vsgopenmw-dev/vsgopenmw#9

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[AnyOldName3]

Have you checked nothing would be affected by any of the policy changes between 3.7 and 3.24. Changing cmake_minimum_required changes all policies introduced in the version range from their OLD behaviour to their NEW behaviour.

[psi29a]

There have been no changes (oddly enough), here is the complete output:

/Applications/CLion.app/Contents/bin/cmake/mac/aarch64/bin/cmake -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_MAKE_PROGRAM=/Applications/CLion.app/Contents/bin/ninja/mac/aarch64/ninja -G Ninja -S /Users/psi29a/Workspace/private/VulkanSceneGraph -B /Users/psi29a/Workspace/private/VulkanSceneGraph/cmake-build-relwithdebinfo
-- The CXX compiler identification is AppleClang 15.0.0.15000040
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /Library/Developer/CommandLineTools/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Reading 'vsg_...' macros from /Users/psi29a/Workspace/private/VulkanSceneGraph/cmake/vsgMacros.cmake - look there for documentation
-- Found Vulkan: /opt/homebrew/lib/libvulkan.dylib (found suitable version "1.3.268", minimum required is "1.1.70.0") found components: glslang SPIRV-Tools glslc glslangValidator 
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE  
-- The following REQUIRED packages have been found:

 * Vulkan (required version >= 1.1.70.0)
 * Threads

-- Configuring done (4.8s)
-- Generating done (0.0s)
-- Build files have been written to: /Users/psi29a/Workspace/private/VulkanSceneGraph/cmake-build-relwithdebinfo

[Finished]

[AnyOldName3]

This changes the behaviour of 72 CMake policies. It's unlikely that none of them would have affected anything. The differences might only end up breaking setups you've not tried, or might only result in runtime changes. There're probably a few changes that mean something that's being handled explicitly can be simplified as CMake will do it implicitly. You really need to look through the policy list https://cmake.org/cmake/help/latest/manual/cmake-policies.7.html#manual:cmake-policies(7) and check each one rather than just try building and assume everything is fine if it looks like it worked.

[psi29a]

The differences might only end up breaking setups you've not tried

This is a sure fire way to prevent any commit from being merged. I hope you understand that.

Which is why we try to make sure the CI is as robust as possible, within reason. It is impossible to test every place that VSG or any library would be used on.

Thanks for the link, I'll review.

Building is not enough, I've validated on 3 platforms except Windows. So I'll need someone's help making sure that it actually runs there.

[AnyOldName3]

This is a sure fire way to prevent any commit from being merged. I hope you understand that.

Yes. Changing what's passed to cmake_minimum_required is a big deal, and needs an abundance of caution. It's not as minor as doing something like changing the C++ language standard, and that's already a pretty big deal.