Properly checkouting git submodules in a given repo

[nunoguedelha]

This is is not to point out a real issue, but more a heads up and to verify with you, @GiulioRomualdi , @traversaro , that we are doing the same thing when selecting a given commit of a repo containing git submodules. Let's consider the example of https://github.com/oxfordcontrol/osqp.git (I open the issue here because of osqp being an external repo obviously):

• if we checkout the branch master (commit 6fb6db9), the respective commit value for the submodule lin_sys/direct/qdldl/qdldl_sources is 12d56ee (tag v0.1.4).

• if we checkout the tag v0.6.0 (commit 0baddd3), the respective commit value for the submodule lin_sys/direct/qdldl/qdldl_sources should be 70596af (commit message Merge pull request #22 ...), but in fact, the actual commit checked out in the submodule stays the same: 12d56ee (tag v0.1.4). This "discrepancy" then appears as a change in the working tree of the parent repo osqp:

  
  $ git status
  HEAD detached at v0.6.0
  Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)
  
  modified:   lin_sys/direct/qdldl/qdldl_sources (new commits)

no changes added to commit (use "git add" and/or "git commit -a")

So in order to select the real `osqp` version `v0.6.0`, we also have to checkout `70596af` (commit message `Merge pull request #22 ...`) in the submodule.

Is this what we are doing when evaluating/selecting the desired versions of `osqp`?

[traversaro]

Is this what we are doing when evaluating/selecting the desired versions of osqp?

I am not really sure what CMake's ExternalProject does internally, but at least for the robotology-superbuild on a clean build (so no subsequent tag changes), it seems that the correct version of qdldl is used.

[nunoguedelha]

So there would be a problem only if we first clone master then checkout an earlier commit. I get it.

[nunoguedelha]

As a side note, git submodule update --recursive will checkout the proper commit of the submodule. I was reading this tutorial: https://git-scm.com/book/en/v2/Git-Tools-Submodules.