UX improvement for typos in allow-newer

[parsonsmatt]

If I write this in my cabal.project file:

allow-newer:
    http-api-data:base
  , postgrseql-simple:base

then cabal doesn't complain, but it also tells me that the base version is Too New for postgresql-simple. It takes a minute to scan the text and realize my typo.

It'd be nice if allow-newer failed if the package name wasn't in the dependency set.

[Mikolaj]

I took me 2 days and I'm still not certain: is the order of packages wrong in each pair? If so, a good idea to warn.

[ulysses4ever]

@Mikolaj no, it's the name of package that is a problem: it has a typo. A more clear reproducer would be to say blah:base...

I wonder if this has been discussed before. Not clear to me that constraints that solver ended up not using should be an error.