https://ubuntu.com/about/release-cycle

As you can see at the link above, the period for "hardware and maintenance updates" ends 5 years after a LTS release, so for Ubuntu 18.04 that ends during April 2023.

As far as I know, the extra 5 years of Extended Security Maintenance requires paying Ubuntu/Canonical money.

For brevity, I will call an Ubuntu LTS release "expired" if it is over 5 years since its initial release date. So Ubuntu 16.04 is expired now, and Ubuntu 18.04 is expired some time this month, but definitely by May 1, 2023.

It seems reasonable to me that for building p4c from source code (and perhaps for any other open source p4lang project), it is reasonable to no longer go to significant extra work to support that for expired Ubuntu LTS releases. By that time, there are always 2 additional LTS releases available to use.

Do we want to make this "official p4c developer/maintainer policy"? That is, if p4c fails to compile from source on an expired Ubuntu release, it is less likely that anyone will devote any effort to fixing such isses? And in fact we might update some build scripts to take advantage of later versions of the build tools available as the default installable packages on later Ubuntu releases, even if that is known to break the build for expired Ubuntu versions?

Fabian Ruffy and others are currently dealing with p4c build system issues that are known to cause the build to fail for Ubuntu 18.04. If some kind of majority of p4c developers agree that it is OK for builds of p4c on expired Ubuntu releases to no longer work, his changes can be made easier.