pkg/57852: pkg_install should manage three-way merge of conf files on update

[campbell+netbsd%mumble.net@localhost]

>Number:         57852
>Category:       pkg
>Synopsis:       pkg_install should manage three-way merge of conf files on update
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Jan 14 16:25:00 +0000 2024
>Originator:     Taylor R Campbell
>Release:        current
>Organization:
The NetBS3 Pkginstallation
>Environment:
>Description:
Config files under PKG_SYSCONFBASE, e.g. /usr/pkg/etc, are always installed under /usr/pkg/share/examples first and then copied to /usr/pkg/etc, via the CONF_FILES machinery in pkgsrc.  So we always have the pristine version of each config file.

pkg_add should take advantage of this on updates to provide three-way merges of config files, since it always has the old and new pristine files under /usr/pkg/share/examples, and the locally modified config file in /usr/pkg/etc.
>How-To-Repeat:
update packages and deal with config file changes
>Fix:
Yes, please!