pacman hook to list new optional dependencies after an upgrade

display-optdepends-pre.hook

[Trigger]
Operation = Install
Operation = Upgrade
Type = Package
Target = *

[Action]
Description = Preparing to detect new optional dependencies...
Depends = pyalpm
When = PreTransaction
Exec = /etc/pacman.d/display_optdepends.py pre

display-optdepends.hook

[Trigger]
Operation = Install
Operation = Upgrade
Type = Package
Target = *

[Action]
Description = Detecting new optional dependencies...
Depends = pyalpm
When = PostTransaction
Exec = /etc/pacman.d/display_optdepends.py post

display_optdepends.py

#!/usr/bin/env python3
#
# pacman hook to list new optional dependencies
# requires pyalpm
# Copyright (C) 2017 A. Bosch <code@progandy.de>
# 
#   This program is free software; you can redistribute it and/or modify
#   it under the terms of the GNU General Public License as published by
#   the Free Software Foundation; either version 2 of the License, or
#   (at your option) any later version.
#
#   This program is distributed in the hope that it will be useful,
#   but WITHOUT ANY WARRANTY; without even the implied warranty of
#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#   GNU General Public License for more details.
#
#   You should have received a copy of the GNU General Public License
#   along with this program; if not, write to the Free Software
#   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#
import sys
from pycman import config
import pyalpm
import json
import os.path

def get_optdeps(hpm):
    odeps={}
    for pkg in hpm.get_localdb().pkgcache:
        for odep in pkg.optdepends:
            name, sep, desc = odep.partition(':')
            odeps.setdefault(name.strip(), {})[pkg.name] = desc.strip()
    return odeps

def get_installed_str(hlist, name):
    if pyalpm.find_satisfier(hlist, name):
        return "[installed]"
    return ""



def main():
    hpm = config.init_with_config("/etc/pacman.conf")
    cachefile= hpm.dbpath.rstrip('/') + '/local_optdeps.json'

    if len(sys.argv) != 2:
        return

    if sys.argv[1] == "pre":
        if not os.path.isfile(cachefile):
            with open(cachefile, 'w') as f:
                json.dump(get_optdeps(hpm), f)
    elif sys.argv[1] == "post":
        newdeps = get_optdeps(hpm)
        olddeps = {}
        with open(cachefile, 'r') as f:
            olddeps = json.load(f)
        with open(cachefile, 'w') as f:
            json.dump(newdeps, f)

        hinst = hpm.get_localdb().pkgcache

        for odep in newdeps:
            first = True
            for request in newdeps[odep]:
                if odep not in olddeps or request not in olddeps[odep]:
                        if first:
                            print(odep, get_installed_str(hinst, odep), "suggested by:")
                            first = False
                        print(" ", request, ":", newdeps[odep][request])

if __name__ == "__main__":
    main()