L2SS-176: Cache git version to avoid reporting the disk instead of loaded version

devices/util/lofar_git.py

 import git # pip3 install gitpython
 import os
+from functools import lru_cache
 
 def get_repo(starting_directory: str = os.path.dirname(__file__)) -> git.Repo:
     """ Try finding the repository by traversing up the tree.
@@ -27,13 +28,28 @@ def get_repo(starting_directory: str = os.path.dirname(__file__)) -> git.Repo:
     raise git.InvalidGitRepositoryError("Could not find git repository root in {}".format(starting_directory))
 
 
+@lru_cache(maxsize=None)
 def get_version(repo: git.Repo = None) -> str:
-    """ Return a version string for the current commit. """
+    """ Return a version string for the current commit.
+
+    There is a practical issue: the repository changes over time, f.e. switching branches with 'git checkout'. We want
+    to know the version that is running in memory, not the one that is on disk.
+
+    As a work-around, we cache the version information, in that it is at least consistent. It is up to the caller
+    to request the version early enough. """
 
     if repo is None:
         repo = get_repo()
 
-    return "{} [{}{}]".format(repo.active_branch, repo.commit(), " (dirty)" if repo.is_dirty() else "")
+    return "{} [{}]{}".format(repo.active_branch, repo.commit(), " (dirty)" if repo.is_dirty() else "")
+
+
+# at least cache the current repo version immediately
+try:
+    _ = get_version()
+except:
+    pass
+
 
 if __name__ == "__main__":
     print(get_version())