import ci/ci-commitmessage-submodules.sh from ostree

This would be useful here as well. Added small tweaks that I intend to
upstream (using realpath and --no-merges).

Closes: #773
Approved by: cgwalters

.redhat-ci.yml

@@ -11,6 +11,7 @@ container:
     image: registry.fedoraproject.org/fedora:25
 
 tests:
+  - ci/ci-commitmessage-submodules.sh
   - ci/build-check.sh
 
 timeout: 30m

ci/ci-commitmessage-submodules.sh

@@ -0,0 +1,55 @@
+#!/bin/bash
+set -xeuo pipefail
+
+# Copyright 2017 Colin Walters <walters@verbum.org>
+# Licensed under the new-BSD license (http://www.opensource.org/licenses/bsd-license.php)
+
+# This script is intended to be used as a CI gating check
+# that if a submodule is changed, the commit message contains
+# the text:
+#
+#  Update submodule: submodulepath
+#
+# It's very common for people to accidentally change submodules, and having this
+# requirement is a small hurdle to pass.
+
+# if running under RHCI, use the branch/PR HEAD actually
+# being tested rather than the merge sha
+HEAD=${RHCI_COMMIT:-HEAD}
+
+tmpd=$(mktemp -d)
+touch ${tmpd}/.tmpdir
+cleanup_tmp() {
+    # This sanity check ensures we don't delete something else
+    if test -f ${tmpd}/.tmpdir; then
+        rm -rf ${tmpd}
+    fi
+}
+trap cleanup_tmp EXIT
+
+gitdir=$(realpath $(pwd))
+# Create a temporary copy of this (using cp not git clone) so git doesn't
+# try to read the submodules from the Internet again.  If we wanted to
+# require a newer git, we could use `git worktree`.
+cp -a ${gitdir} ${tmpd}/workdir
+cd ${tmpd}/workdir
+git log --pretty=oneline origin/master..$HEAD | while read logline; do
+    commit=$(echo ${logline} | cut -f 1 -d ' ')
+    git diff --name-only ${commit}^..${commit} > ${tmpd}/diff.txt
+    git log -1 ${commit} > ${tmpd}/log.txt
+    echo "Validating commit for submodules: $commit"
+    sed -e 's,^,# ,' < ${tmpd}/log.txt
+    git checkout -q "${commit}"
+    git submodule update --init
+    git submodule foreach --quiet 'echo $path'| while read submodule; do
+        if grep -q -e '^'${submodule} ${tmpd}/diff.txt; then
+            echo "Commit $commit modifies submodule: $submodule"
+            expected_match="Update submodule: $submodule"
+            if ! grep -q -e "$expected_match" ${tmpd}/log.txt; then
+                echo "error: Commit message for ${commit} changes a submodule, but does not match regex ${expected_match}"
+                exit 1
+            fi
+            echo "Verified commit $commit matches regexp ${expected_match}"
+        fi
+    done
+done