avoid package upgrade headaches when transitioning to flux-foundry

[garlick]

Problem: flux-foundry is splitting installed libraries and headers out of flux-core, which introduces new package conflicts and dependencies.

Since this is a fairly common use case for package managers, there is good documentation for both deb and rpm packages:

https://www.debian.org/doc/debian-policy/ch-relationships.html#overwriting-files-in-other-packages

https://docs.fedoraproject.org/en-US/packaging-guidelines/Conflicts/#_splitting_packages

This issue can be closed once we've got the flux-foundry debian control file updated and added recommendations for other framework projects.

[garlick]

Deb experiment:

In this repo I added this and locally tagged 0.0.0

diff --git a/debian/control b/debian/control
index efc88ec..c561434 100644
--- a/debian/control
+++ b/debian/control
@@ -9,6 +9,8 @@ Build-Depends:
   python3-ply,
   python3-sphinx
 
+Replaces: flux-core (<< 0.74.0)
+Breaks: flux-core (<< 0.74.0)
 Homepage: https://github.com/flux-framework/flux-foundry
 Package: flux-foundry
 Architecture: any

In a flux core branch, I modified the build system to not install hostlist products, added the following, and locally tagged 0.74.0

diff --git a/debian/control b/debian/control
index 1b8bfdc56..c60b8ffb2 100644
--- a/debian/control
+++ b/debian/control
@@ -6,6 +6,7 @@ Standards-Version: 4.1.2
 Build-Depends:
   debhelper (>= 10),
   flux-security (>= 0.14.0),
+  flux-foundry,
   libsystemd-dev (>= 0.23),
   libarchive-dev,
   uuid-dev,

With flux-core 0.73.0 installed, I was then able to just do

$ sudo dpkg -i flux-core_0.74.0_amd64.deb flux-foundry_0.0.0_amd64.deb
(Reading database ... 268757 files and directories currently installed.)
Preparing to unpack flux-core_0.74.0_amd64.deb ...
Unpacking flux-core (0.74.0) over (0.73.0) ...
Selecting previously unselected package flux-foundry.
Preparing to unpack flux-foundry_0.0.0_amd64.deb ...
Unpacking flux-foundry (0.0.0) ...
Setting up flux-core (0.74.0) ...
Could not execute systemctl:  at /usr/bin/deb-systemd-invoke line 142.
Setting up flux-foundry (0.0.0) ...
Processing triggers for libc-bin (2.35-0ubuntu3.9) ...
Processing triggers for man-db (2.10.2-1) ...

I assume the non-fatal systemd error probably is because i didn't have a valid configuration in place.