GIT_SUBMODULE fix: File not found .git/HEAD error

[Bjoe]

• I've checked this Git style guide. Yes
• I've checked this CMake style guide. Yes
• My change will work with CMake 3.2 (minimum requirement for Hunter). Yes
• I will try to keep this pull request as small as possible and will try not to mix unrelated features. Yes

This PR will fix a "File not found .git/HEAD" error, when you use GIT_SUBMODULE in hunter_config()

[NeroBurner]

I can't reproduce the error you are fixing. Using the latest release v0.23.250 I modified Vulkan-Loader to use Vulkan-Headers from a submodule

https://github.com/NeroBurner/Vulkan-Loader/tree/hunter_with_submodule

with cmake -H. -B_build -DHUNTER_ENABLED=ON -DHUNTER_STATUS_DEBUG=ON the hunter step works as expected

can you provide a minimal configuration for a failing build and maybe the cmake output?

[Bjoe]

Yes sure ... let me figured out and I will send you when it fails ... give me some time

[Bjoe]

@NeroBurner Good questioned/finding :-) ... I already found an error in my first solution ...

To reproduce the error do following:

1. Checkout your repo https://github.com/NeroBurner/Vulkan-Loader hunter_with_submodule branch
2. Change into the folder cd Vulkan-Loader
3. Remove subrepo git rm Vulkan-Headers
4. Clone Vulkan headers git clone https://github.com/NeroBurner/Vulkan-Headers.git
5. Add submodule git submodule add ./Vulkan-Headers Vulkan-Headers

Now try to build and you will get following error:

.......
-- Found Git: /usr/bin/git (found version "2.20.1") 
-- [hunter *** DEBUG *** 2020-03-22T14:32:36] Using git executable: /usr/bin/git

[hunter ** INTERNAL **] File not found: .git/refs/heads/hunter-1.2.133
[hunter ** INTERNAL **] [Directory:/home/developer/Development/hunter-wk/Vulkan-Loader/cmake/Hunter]

------------------------------ ERROR -----------------------------
    https://hunter.readthedocs.io/en/latest/reference/errors/error.internal.html
------------------------------------------------------------------

CMake Error at /home/developer/.hunter/_Base/Download/Hunter/0.23.250/0e6ce30/Unpacked/cmake/modules/hunter_error_page.cmake:12 (message):
Call Stack (most recent call first):
  /home/developer/.hunter/_Base/Download/Hunter/0.23.250/0e6ce30/Unpacked/cmake/modules/hunter_internal_error.cmake:13 (hunter_error_page)
  /home/developer/.hunter/_Base/Download/Hunter/0.23.250/0e6ce30/Unpacked/cmake/modules/hunter_pack_git_submodule.cmake:167 (hunter_internal_error)
  /home/developer/.hunter/_Base/Download/Hunter/0.23.250/0e6ce30/Unpacked/cmake/modules/hunter_config.cmake:94 (hunter_pack_git_submodule)
  cmake/Hunter/config.cmake:1 (hunter_config)
  /home/developer/.hunter/_Base/Download/Hunter/0.23.250/0e6ce30/Unpacked/cmake/modules/hunter_calculate_config_sha1.cmake:40 (include)
  /home/developer/.hunter/_Base/Download/Hunter/0.23.250/0e6ce30/Unpacked/cmake/modules/hunter_apply_gate_settings.cmake:155 (hunter_calculate_config_sha1)
  /home/developer/.hunter/_Base/Download/Hunter/0.23.250/0e6ce30/Unpacked/cmake/modules/hunter_finalize.cmake:73 (hunter_apply_gate_settings)
  /home/developer/.hunter/_Base/Download/Hunter/0.23.250/0e6ce30/Unpacked/cmake/modules/hunter_add_package.cmake:23 (hunter_finalize)
  external/CMakeLists.txt:45 (hunter_add_package)

[NeroBurner]

I think this will break if you add the submodule with an relative path. For example I can add the Vulkan Headers with git submodule add ../../NeroBurner/Vulkan-Headers and git will download the submodule with the same method as the parent git repo was downloaded (git+ssh, https, https with a user token)