From a beginner point of vu, it seems a bit odd to not get any errors when building a project that doesn't install anything due to a lack of (public_name ...) or other things.

For instance, see the PR of someone who made the mistake and would have been unnoticed if I hadn't looked at the project more in details: ocaml/opam-repository#15262

For example, if you define a project as such:

$ echo '(library (name some_package))' > dune
$ touch some_package.opam

dune build -p some_package doesn't do build anything but produces some_package.install which doesn't install anything (except an empty META file). This is prone to mistake from beginners trying to release their first package in opam and I think dune should raise an error to avoid this type of mistake.