pkg/58943: pkgin doesn't warn if installed packages vanished and are broken by shlib major bumps

[campbell+netbsd%mumble.net@localhost]

>Number:         58943
>Category:       pkg
>Synopsis:       pkgin doesn't warn if installed packages vanished and are broken by shlib major bumps
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Dec 28 17:05:00 +0000 2024
>Originator:     Taylor R Campbell
>Release:        current, 2024Q4
>Organization:
The NotPackaged Installation
>Environment:
>Description:
User had packages including firefox installed from 2024Q3.

User configured pkgin to point at not-yet-fully-baked 2024Q4 repo URL, with (a) icu major bump 75 -> 76, but (b) no firefox.

User ran pkgin update && pkgin upgrade.

pkgin reported various packages to update but didn't warn that the update would break firefox because of icu major bump, with no corresponding firefox update to fix it:

calculating dependencies...done.

66 packages to refresh:
  ...

76 packages to upgrade:
  ... icu-76.1nb1 ...

0 to remove, 66 to refresh, 76 to upgrade, 2 to install
644M to download, 298M of additional disk space will be used

proceed ? [Y/n] y
...
pkg_install warnings: 0, errors: 0
reading local summary...
processing local summary...

Switching to the unfinished 2024Q4 URL may be reasonably described as user error.  But pkgin should alert that this update will break packages.
>How-To-Repeat:
1. install a package foo that depends on bar with shlib libbar.so.1
2. point pkgin at a binary package repository with an update for bar but _no foo package_
3. pkgin upgrade
4. try to use foo
>Fix:
Yes, please!