We will start using the latest Ubuntu LTS version for our CI no earlier than 3 months after its release and, ideally, no more than 12 months after its release.
When a formula needs a newer GCC because our host GCC in CI is too old, we needed to make that formula depend on a newer Homebrew GCC. All C++ dependents of that formula immediately acquire a dependency on Homebrew GCC as well. While we have taken the steps to make sure this no longer holds up GCC updates, it still creates a maintenance burden. This problem is more likely for formula which are very actively maintained and try to use newer features of C++. We decided that we shouldn't have a maintenance burden for formulae which are doing the right thing by staying up to date. It makes a lot of sense for Homebrew maintainers to submit upstream fixes when formulae are not working with newer compilers. It makes a lot less sense for Homebrew maintainers to submit fixes because our host compiler is too old.
Note that `glibc` will need to be installed for more users as their `glibc` version will often be too old: disk space is cheap and we have can handle this situation for our users. This situation will often arise when update to a new LTS version and adoption of the new Ubuntu is still low during the first months. For the same reasons as above: we prefer to stay on the bleeding edge and give our users a gentle nudge to think about updating their OS.
