opam file generation could be made less error-prone

[samoht]

I would expect the generation of opam file from dune-project to be fool-proof, ie. warm when there are clear mistakes/typos. Right now, it doesn't.

For instance, if you write:

(depends
   (alcotest :with_test)
   ...

This will happily generates an opam file containing "alcotest" {with_test} which will make opam install . --deps -t very confused (basically it'll just ignore that variable). I would have expected the conversion to either warn that this variable seems suspiciously close to with-test or just fail, as this variable isn't defined anywhere.