CI: add CODEOWNERS file sanity check (MR 4662)

* Check for space indentation instead of tabs
* Check that an entry actually exists
* Check that a directory ends in a slash, otherwise GitLab seems to
  ignore it

.ci/codeowners.sh

@@ -0,0 +1,43 @@
+#!/bin/sh -e
+# Description: verify CODEOWNERS file is sane
+# https://postmarketos.org/pmb-ci
+
+# TODO Future improvements:
+# * Check that all devices in main/community have someone in CODEOWNERS
+# * Check that GitLab user actually exists (e.g. deleted account, account with
+#   changed user name)
+
+if grep -q "  " CODEOWNERS; then
+	echo
+	echo "ERROR: Found space indentation in CODEOWNERS."
+	echo "ERROR: Please indent with tab characters."
+	grep "  " CODEOWNERS
+	echo
+	exit 1
+fi
+
+fail=0
+tmppipe=$(mktemp -u)
+mkfifo "$tmppipe"
+grep -v "^#" CODEOWNERS | cut -d'	' -f1  > "$tmppipe" &
+while IFS= read -r line; do
+	[ -z "$line" ] && continue
+
+	# Check if entry generally exists
+	# shellcheck disable=SC2086
+	ls $line >/dev/null 2>&1 || { fail=1; echo "Non-existing: $line"; }
+
+	# Check that directories end with a slash
+	# shellcheck disable=SC2086
+	if test -d "$(ls -d $line)"; then
+		echo "$line" | grep -q '/$' || { fail=1; echo "Missing trailing slash: $line"; }
+	fi
+done < "$tmppipe"
+rm "$tmppipe"
+
+if [ "$fail" = 1 ]; then
+	echo
+	echo "ERROR: Invalid CODEOWNERS entries, see above."
+	echo
+	exit 1
+fi

.gitlab-ci.yml

@@ -60,6 +60,7 @@ shellcheck-grep:
     - .ci/lib/gitlab_prepare_ci.sh
     - .ci/shellcheck.sh
     - .ci/grep.sh
+    - .ci/codeowners.sh
 
 editor-config:
   stage: lint