A git hook that automatically adds a change-id to the commit message.

commit-msg

#!/bin/sh
# From Gerrit Code Review 2.1.2-rc2-33-g7e30c72
#
# Part of Gerrit Code Review (http://code.google.com/p/gerrit/)
#
# 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.
#

CHANGE_ID_AFTER="Bug|Issue"
MSG="$1"

# Check for, and add if missing, a unique Change-Id
#
add_ChangeId() {
	clean_message=$(sed -e '
		/^diff --git a\/.*/{
			s///
			q
		}
		/^Signed-off-by:/d
		/^#/d
	' "$MSG" | git stripspace)
	if test -z "$clean_message"
	then
		return
	fi

	if grep -i '^Change-Id:' "$MSG" >/dev/null
	then
		return
	fi

	id=$(_gen_ChangeId)
	perl -e '
		$MSG = shift;
		$id = shift;
		$CHANGE_ID_AFTER = shift;

		undef $/;
		open(I, $MSG); $_ = <I>; close I;
		s|^diff --git a/.*||ms;
		s|^#.*$||mg;
		exit unless $_;

		@message = split /\n/;
		$haveFooter = 0;
		$startFooter = @message;
		for($line = @message - 1; $line >= 0; $line--) {
			$_ = $message[$line];

			($haveFooter++, next) if /^[a-zA-Z0-9-]+:/;
			next if /^[ []/;
			$startFooter = $line if ($haveFooter && /^\r?$/);
			last;
		}

		@footer = @message[$startFooter+1..@message];
		@message = @message[0..$startFooter];
		push(@footer, "") unless @footer;

		for ($line = 0; $line < @footer; $line++) {
			$_ = $footer[$line];
			next if /^($CHANGE_ID_AFTER):/i;
			last;
		}
		splice(@footer, $line, 0, "Change-Id: I$id");

		$_ = join("\n", @message, @footer);
		open(O, ">$MSG"); print O; close O;
	' "$MSG" "$id" "$CHANGE_ID_AFTER"
}
_gen_ChangeIdInput() {
	echo "tree $(git write-tree)"
	if parent=$(git rev-parse HEAD^0 2>/dev/null)
	then
		echo "parent $parent"
	fi
	echo "author $(git var GIT_AUTHOR_IDENT)"
	echo "committer $(git var GIT_COMMITTER_IDENT)"
	echo
	printf '%s' "$clean_message"
}
_gen_ChangeId() {
	_gen_ChangeIdInput |
	git hash-object -t commit --stdin
}


add_ChangeId