git-prod

#!/bin/bash -e

# Switch to top level of repository
base=$(git rev-parse --show-toplevel 2> /dev/null || true)
if [ -z "$base" ]; then
	echo "Not in a git repository" >&2
	exit 1
fi
cd $base

# Check for any uncommitted changes
# Even though they won't be included in the final commit,
# make sure that they'll be included in the history.
if git diff --quiet HEAD; then
	:
else
	echo "Uncommitted changes, aborting" >&2
	exit 1
fi

# Get info about the branch that is to be merged
to_merge=$1
if [ "x$to_merge" = "x" ]; then
	echo "No branch to merge specified" >&2
	exit 1
fi
tree=$(git rev-parse --verify "$to_merge^{tree}")

# Ensure that there's something to merge
if [ -z "$(git rev-list -n 1 ..$to_merge)" ]; then
	echo "Branch is up to date" >&2
	exit
fi

# Generate commit message
commit_msg=.git/COMMIT_EDITMSG
echo "Updating to $to_merge" > $commit_msg
echo "" >> $commit_msg
git log --reverse --format=' * %s' "..$to_merge" >> $commit_msg

# Provide opportunity to edit commit message
editor $commit_msg

# Remove comment lines, and ensure that there's a commit message
perl -ni \
	-e 'next if /^#/;' \
	-e '$msg = 1 unless /^\s*$/;' \
	-e 'print;' \
	-e 'END { unless($msg) { print "No commit message, aborting\n"; exit 1 } }' \
	$commit_msg

# Create the merge commit
merged=$(git commit-tree $tree -p HEAD -p $to_merge < $commit_msg)

# Update current branch to the new commit
git reset --hard $merged