git-version-bump-filter

#!/bin/bash
set -eo pipefail

v_date=
[[ "$1" != -d && "$1" != --date-ver ]] || { v_date=t; shift; }

[[ -n "$1" ]] || {
	files=( $(awk '$2=="filter=version-bump" {sub(/^\//,"",$1); print $1}' .gitattributes) )
	[[ "${#files[@]}" -eq 0 ]] || {
		git diff -U0 HEAD -- "${files[@]}" |
				awk '/^@@/ {p=1; next} p&&/^[-+]/ {print; next} p {p=0}' |
				grep -vq -e '# git-version: [^ ]\+' \
			&& { echo "ERROR: uncomitted changes detected, aborting revert/bump"; exit 1; } ||:
		touch "${files[@]}" && git checkout "${files[@]}"; }
	exit 0; }

# Simple 1.2.<commit> version replacement
[[ -n "$v_date" ]] || {
	v=$(git log --pretty=format:x -- "$1" | wc -l)
	exec sed \
		-e '/# git-version: py-tuple\(-[0-9]\)*$/ s/\(.* *= *\([0-9]\+, *\)*\)[0-9]\+/\1'"$v"'/' \
		-e '/# git-version: py-str\(-[0-9]\)*$/ s/\(.* *= *['\''"]\([0-9]\+\.\)*\)[0-9]\+\(['\''"]\)/\1'"$v"'\3/'; }

# Full replacement with <year>.<month>.<commits-since-month-start>
v=$(printf '%(%y.%m)T' -1).`
	`$(git log --since=$(printf '%(%Y-%m-01)T' -1) --pretty=format:x -- "$1" | sed '$a\' | wc -l)
exec sed \
	-e '/# git-version: py-tuple\(-[0-9]\)*$/ s/\(.* *= *\)\([0-9]\+, *\)*[0-9]\+/\1'"${v//./,}"'/' \
	-e '/# git-version: py-str\(-[0-9]\)*$/ s/\(.* *= *['\''"]\)\([0-9]\+\.\)*[0-9]\+\(['\''"]\)/\1'"$v"'\3/'