misc: Add gerrit commit message hook to pre-commit

This pre-commit hook adds the Change-ID etc. to the commit message.

Change-Id: I43b239468ab60ce1a8aaabb53dd6905819a2ce05
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/62575
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

.pre-commit-config.yaml

@@ -81,3 +81,9 @@ repos:
     language: system
     stages: [commit-msg]
     description: 'The gem5 commit message checker hook.'
+  - id: gerrit-commit-msg-job
+    name: gerrit commit message job
+    entry: util/gerrit-commit-msg-hook
+    language: system
+    stages: [commit-msg]
+    description: 'Adds Change-ID to the commit message. Needed by Gerrit.'

util/gerrit-commit-msg-hook

@@ -0,0 +1,104 @@
+#!/bin/sh
+# From Gerrit Code Review 3.6.1-1565-g2ee3d30913
+#
+# Part of Gerrit Code Review (https://www.gerritcodereview.com/)
+#
+# Copyright (C) 2009 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -u
+
+# avoid [[ which is not POSIX sh.
+if test "$#" != 1 ; then
+  echo "$0 requires an argument."
+  exit 1
+fi
+
+if test ! -f "$1" ; then
+  echo "file does not exist: $1"
+  exit 1
+fi
+
+# Do not create a change id if requested
+if test "false" = "$(git config --bool --get gerrit.createChangeId)" ; then
+  exit 0
+fi
+
+# Do not create a change id for squash commits.
+if head -n1 "$1" | grep -q '^squash! '; then
+  exit 0
+fi
+
+if git rev-parse --verify HEAD >/dev/null 2>&1; then
+  refhash="$(git rev-parse HEAD)"
+else
+  refhash="$(git hash-object -t tree /dev/null)"
+fi
+
+random=$({ git var GIT_COMMITTER_IDENT ; echo "$refhash" ; cat "$1"; } | git hash-object --stdin)
+dest="$1.tmp.${random}"
+
+trap 'rm -f "$dest" "$dest-2"' EXIT
+
+if ! git stripspace --strip-comments < "$1" > "${dest}" ; then
+   echo "cannot strip comments from $1"
+   exit 1
+fi
+
+if test ! -s "${dest}" ; then
+  echo "file is empty: $1"
+  exit 1
+fi
+
+reviewurl="$(git config --get gerrit.reviewUrl)"
+if test -n "${reviewurl}" ; then
+  token="Link"
+  value="${reviewurl%/}/id/I$random"
+  pattern=".*/id/I[0-9a-f]\{40\}$"
+else
+  token="Change-Id"
+  value="I$random"
+  pattern=".*"
+fi
+
+if git interpret-trailers --parse < "$1" | grep -q "^$token: $pattern$" ; then
+  exit 0
+fi
+
+# There must be a Signed-off-by trailer for the code below to work. Insert a
+# sentinel at the end to make sure there is one.
+# Avoid the --in-place option which only appeared in Git 2.8
+if ! git interpret-trailers \
+         --trailer "Signed-off-by: SENTINEL" < "$1" > "$dest-2" ; then
+  echo "cannot insert Signed-off-by sentinel line in $1"
+  exit 1
+fi
+
+# Make sure the trailer appears before any Signed-off-by trailers by inserting
+# it as if it was a Signed-off-by trailer and then use sed to remove the
+# Signed-off-by prefix and the Signed-off-by sentinel line.
+# Avoid the --in-place option which only appeared in Git 2.8
+# Avoid the --where option which only appeared in Git 2.15
+if ! git -c trailer.where=before interpret-trailers \
+         --trailer "Signed-off-by: $token: $value" < "$dest-2" |
+     sed -e "s/^Signed-off-by: \($token: \)/\1/" \
+         -e "/^Signed-off-by: SENTINEL/d" > "$dest" ; then
+  echo "cannot insert $token line in $1"
+  exit 1
+fi
+
+if ! mv "${dest}" "$1" ; then
+  echo "cannot mv ${dest} to $1"
+  exit 1
+fi