Can't build from source with CMake 3.10.2 with one cmake call. Depends on FindVulkan updates in CMake 3.21 or installation of Vulkan-Headers

[dneto0]

Describe the bug

Can't build from source with CMake 10.0.2

CMakeLists.txt says CMake required version is 10.0.2
But #1061 switched discovery of Vulkan::Headers to use the FindVulkan built into CMake. That was introduced in CMAKE 3.21. https://cmake.org/cmake/help/latest/release/3.21.html#modules
in this commit: Kitware/CMake@668ba68

Environment (please complete the following information):

• OS: Linux
• Bitdepth: n/a
• GPU: n/a
• Graphics Driver: n/a
• SDK or header version if building from repo: Vulkan headers v 1.3.237
• Enabled layers: none

To Reproduce
Steps to reproduce the behavior:
Currently reducing this down, but i found this by trying to roll Amber's dependencies forward.
See google/amber#1005

VK_LOADER_DEBUG output
Attach output when running with the environment variable VK_LOADER_DEBUG=all

Additional context
Found when trying to roll Amber's dependencies forward.

[dneto0]

I'm not sure what the general Cmake requirements are for Vulkan tooling.
If it's still only CMake 3.10, then this is a bug and much of #1061 should be reverted.
If CMake 3.21 is the new baseline then this project's required CMake version should be updated to say that.

[dneto0]

This script reproduces the problem. To run it: "bash x.sh.txt"

x.sh.txt

[juan-lunarg]

CMakeLists.txt says CMake required version is 10.0.2
But #1061 switched discovery of Vulkan::Headers to use the FindVulkan built into CMake. That was introduced in CMAKE 3.21. https://cmake.org/cmake/help/latest/release/3.21.html#modules
in this commit: Kitware/CMake@668ba68

We are not using the FindVulkan support provided by CMake. The loader doesn't even have a call to find_package(Vulkan).

Here is how we find the VulkanHeaders

find_package(VulkanHeaders REQUIRED CONFIG QUIET)

This command searches for VulkanHeadersConfig.cmake and VulkanHeadersConfigVersion.cmake which are created when you install the VulkanHeaders.

See the docs for Vulkan-Headers:

https://github.com/KhronosGroup/Vulkan-Headers/blob/main/BUILD.md

[dneto0]

The output of that repro script ends with:

cmake version 3.10.2

CMake suite maintained and supported by Kitware (kitware.com/cmake).
REPRO: build vulkan-loader from sources with 3.10.2
-- Vulkan-Headers = 1.3.237
********************************************************************************
* NOTE: Not adding target to run update_deps.py automatically.                 *
********************************************************************************
CMake Error at vulkan-loader/CMakeLists.txt:112 (find_package):
  Could not find a package configuration file provided by "VulkanHeaders"
  with any of the following names:

    VulkanHeadersConfig.cmake
    vulkanheaders-config.cmake

  Add the installation prefix of "VulkanHeaders" to CMAKE_PREFIX_PATH or set
  "VulkanHeaders_DIR" to a directory containing one of the above files.  If
  "VulkanHeaders" provides a separate development package or SDK, be sure it
  has been installed.


-- Configuring incomplete, errors occurred!

[dneto0]

See the docs for Vulkan-Headers:

https://github.com/KhronosGroup/Vulkan-Headers/blob/main/BUILD.md

From BUILD.md:

If you are building other Vulkan-related repositories such as Vulkan-Loader, you need to build the install target of this repository and provide the resulting install directory to those repositories.

So by design, it's not possible to build both Vulkan-Headers and Vulkan-Loader with one "cmake" followed by one "build"?
That's the intent, by my reading.

[juan-lunarg]

The vulkan-loader doesn't use add_subdirectory to consume Vulkan-Headers. It uses find_package. The example you sent is invalid.

[juan-lunarg]

So by design, it's not possible to build both Vulkan-Headers and Vulkan-Loader with one "cmake" followed by one "build"?

find_package expects Vulkan-Headers to be installed in a location it can find. The update_deps.py script is intended to speed up this workflow (vckpg/conan are essentially superior versions to update_deps.py).

Essentially update_deps.py finds and installs dependencies into a local external folder CMake then finds by modifying the CMAKE_PREFIX_PATH.

This flat build structure is needed to be conformant with both system packages provided by operating systems and C/C++ package managers.

[juan-lunarg]

I'd like to clarify I have written Vulkan-Headers to be consumable with add_subdirectory for the sake of flexibility. However, the vulkan-loader and the vulkan-validation-layers cannot use add_subdirectory for multiple reasons, basically boiling down to package mangagers and SDK creation.

[juan-lunarg]

I know that's a lot of information I'm throwing at you. Does this make sense @dneto0 ?

[dneto0]

I'd like to clarify I have written Vulkan-Headers to be consumable with add_subdirectory for the sake of flexibility. However, the vulkan-loader and the vulkan-validation-layers cannot use add_subdirectory for multiple reasons, basically boiling down to package mangagers and SDK creation.

Yeah, I guess we disagree what the valid flows should be. Probably not worth arguing over an individual issue like this, and better to escalate / discuss internal to Khronos.

Building "all" or many Vulkan ecosystem projects at once with one cmake invocation is doable and has been done before (e.g. google/vkb and various proposals internal to Khronos). But it bit-rots unless we all agree those are valid and valuable flows.

So we can pause or archive this request/report. I'll figure something else for Amber in the meantime.

[juan-lunarg]

closing since you can build with 3.10.2 as advertised