Update pre commit hook

ci/pre-commit.sh

@@ -2,9 +2,22 @@
 
 # Installing the hook: at root of repo: cd .git/hooks && ln -s ../../ci/pre-commit.sh pre-commit
 
-# stash unstaged changes
-git stash -k -u
+# First, stash index and work dir, keeping only the
+# to-be-committed changes in the working directory.
+old_stash=$(git rev-parse -q --verify refs/stash)
+git stash push --quiet --keep-index --include-untracked --message "os_pre_commit"
+new_stash=$(git rev-parse -q --verify refs/stash)
+
 # Run clang format
 ./ci/clang-format.sh HEAD develop
-# Pop stash
-git stash pop
+RESULT=$?
+[ -f clang_format.patch ] && rm -f clang_format.patch
+
+# Restore changes, only if we stashed something to begin with
+if [ "$old_stash" != "$new_stash" ]; then
+  # stash apply then drop is same as pop
+  git stash apply --index --quiet && git stash drop --quiet
+fi
+
+# If the clang-format script returned non zero, don't allow the commit. The format changes will be in the unstaged queue, ready for approval
+exit $RESULT