Added error handling to prevent checking out non-existent references

Signed-off-by: jakub-nt <175944085+jakub-nt@users.noreply.github.com>

Author: jakub-nt

cfbs/git.py

@@ -249,3 +249,16 @@ def git_check_tracked_changes(scope=["all"]):
         raise CFBSGitError(
             "Failed to run 'git status -s -u' to check for changes."
         ) from cpe
+
+
+def treeish_exists(treeish, repo_path):
+    command = [
+        "git",
+        "rev-parse",
+        "--verify",
+        "--end-of-options",
+        treeish + r"^{object}",
+    ]
+    result = run(command, cwd=repo_path, stdout=DEVNULL, stderr=DEVNULL, check=False)
+
+    return result.returncode == 0

cfbs/internal_file_management.py

@@ -13,7 +13,7 @@
 import shutil
 from typing import Optional
 
-from cfbs.git import ls_remote
+from cfbs.git import ls_remote, treeish_exists
 from cfbs.utils import (
     cfbs_dir,
     cp,
@@ -141,6 +141,9 @@ def _clone_and_checkout(url, path, treeish):
     # NOTE: If any of these shell (git) commands fail, we will exit
     if not os.path.exists(os.path.join(path, ".git")):
         sh("git clone --no-checkout %s %s" % (url, path))
+    if not treeish_exists(treeish, path):
+        raise CFBSExitError("%s not found in %s" % (treeish, url))
+
     sh("git checkout " + treeish, directory=path)