Re #483 Accept main lib in shorthand syntax for dependencies

[mpilgrem]

See:

• Get ready for sublibraries. #483 (comment)

Currently, something like:

spec-version: 0.36.0
name: myPackage
dependencies:
- base

library:
  source-dirs: src

internal-libraries:
  sublib1:
    source-dirs: sub1
  sublib2:
    source-dirs: sub2

executables:
  myExe:
    source-dirs: app
    main: Main.hs
    dependencies:
    - myPackage:{myPackage, sublib1, sublib2}

renders in the Cabal file as (extract):

executable myExe
  main-is: Main.hs
  hs-source-dirs:
      app
  build-depends:
      base
    , myPackage:{sublib1,sublib2}   <<<< The reference to the main library component is missing
  default-language: Haskell2010

This pull request seeks to fix that. A new test is added.

[sol]

This is a great fix, thanks for digging into this!

1. Semantically this is a correct fix.
2. In a way you could say the bug was that the existing code did not pattern match on DependencyName. With that view, a proper fix will do pattern matching (see my suggestion below). This way somebody who reads the code can immediately see that all cases are handled, and none of the constructors are silently ignored. One additional benefit of this approach is that it keeps the order intact.
3. Technically we should probably also pattern match on Dependency in fromCabal. https://hackage-content.haskell.org/package/Cabal-syntax-3.16.1.0/docs/Distribution-Types-Dependency.html#v:Dependency

[sol]

@mpilgrem please go ahead and merge when you're done.