flatpak git wat

$ flatpak-builder build-dir --build-shell=OpenCL-CLHPP info.luxmark.luxmark3.yml
Downloading sources
Fetching git repo https://github.com/KhronosGroup/OpenCL-CLHPP.git, ref refs/tags/v2.0.11
remote: Total 0 (delta 0), reused 0 (delta 0), pack-reused 0
Fetching full git repo https://github.com/ThrowTheSwitch/CMock
Fetching full git repo https://github.com/throwtheswitch/unity.git
Fetching full git repo https://github.com/throwtheswitch/cexception.git
Fetching full git repo https://github.com/throwtheswitch/unity.git
Fetching full git repo https://github.com/ThrowTheSwitch/Unity
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Building module OpenCL-CLHPP in info.luxmark.luxmark3/.flatpak-builder/build/OpenCL-CLHPP-3
========================================================================
Note: switching to 'v2.0.11'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

  git switch -

Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at 3a4d175 Fix the cmake command (#81)
Cloning into 'info.luxmark.luxmark3/.flatpak-builder/build/OpenCL-CLHPP-3/external/CMock'...
fatal: transport 'file' not allowed
fatal: clone of 'file://info.luxmark.luxmark3/.flatpak-builder/git/https_github.com_ThrowTheSwitch_CMock' into submodule path 'info.luxmark.luxmark3/.flatpak-builder/build/OpenCL-CLHPP-3/external/CMock' failed
Failed to clone 'external/CMock'. Retry scheduled
Cloning into 'info.luxmark.luxmark3/.flatpak-builder/build/OpenCL-CLHPP-3/external/CMock'...
fatal: transport 'file' not allowed
fatal: clone of 'file://info.luxmark.luxmark3/.flatpak-builder/git/https_github.com_ThrowTheSwitch_CMock' into submodule path 'info.luxmark.luxmark3/.flatpak-builder/build/OpenCL-CLHPP-3/external/CMock' failed
Failed to clone 'external/CMock' a second time, aborting