Use PrettyField to format cabal file in cabal init

[m-renaud]

This PR replaces the hard-rolled cabal file formatting with PrettyField.

Notable differences:

• Uses 4 space indent instead of 2
• Long lists (extra-source-files, build-depends, etc.) are formatted nicely (not just one long list on a single line)

This resolves #5555.

Open Questions

Unspecified/any version range formatting

It appears not to be possible to pretty-print a dependency of the form: <package-name> with no version constraints, the only matching constructor for VersionRange is AnyVersion which is printed as <package-name> -any. This "unspecified" version range is needed to express a dependency from the package executable to the library within the same package (as is created in --libandexe).

executable foo
    build-depends:
        foo -any

Looking for input on a solution here, we could introduce a new UnspecifiedVersion constructor such that:

parsecSimple "" :: VersionRange
Just UnspecifiedVersion

pretty UnspecifiedVersion
Doc.empty

How to represent standalone comments in PrettyField

Currently (see below) I've created a new constructor in PrettyField for a "commented out" field that can also have comments. Should this be generalized to just PrettyComment? Thoughts on implementation here?

Implementation Notes

In order to re-use the pretty-printing logic I needed to expose the specific list format functions from FieldGrammar.hs. These functions mostly wrap list fields in newtypes so the pretty printer knows how to lay them out.

The one thing that was not easy to express with the existing PrettyField construct was commented out fields that also had comments associated with them. To address this I added a new constructor to the PrettyField type, namely PrettyFieldCommentedOut, this is pretty specific and should probably just be renamed to PrettyComment or similar, lmk what you think about this.

Testing

• Cabal golden file (see updates)
• Manual testing

---

Please include the following checklist in your PR:

• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog (add file to changelog.d directory).
• The documentation has been updated, if necessary.

Please also shortly describe how you tested your change. Bonus points for added tests!

[phadej]

Good start!

[phadej]

About Unspecified/any version range formatting,

I think we can change how Dependency as pretty-printed. Try to modify its Pretty instance.

cabal run hackage-tests roundtrip packagenameprefix

will run roundtrip tests on Hackage data, so if it passes, I'm confident it's ok.

I don't like extra -any, so I'm 👍 about getting rid of them.

EDIT: we don't need to worry about other usages of Pretty Dependency, as most likely Dependency is wrong type there (and something like PackageVersionConstraint should be used instead. If we discover those use cases as a side-effect, we can fix them later.

[m-renaud]

Alright, think I addressed all your comments, lmk if I missed anything!

[phadej]

7.10.3 failure is legit

[m-renaud]

Huh, interesting. The failure is on line 278 in the prependPrefix helper function in mainHs which wasn't touched at all in this PR, even transitively :/ Do you know what's up with that @phadej ?

Also, when trying to build with ghc-7.10.3 locally cryptohash-sha256-0.11.101.0 fails to build:

Build log

``` Failed to build cryptohash-sha256-0.11.101.0. Build log ( /home/mrenaud/.cabal/logs/ghc-7.10.3/cryptohash-sha256-0.11.101.0-541559c14cc76365a19f26bf3fd7c60613e1870c1ce0f5cd3363cf2a9b76d027.log ): Configuring library for cryptohash-sha256-0.11.101.0.. Warning: Packages using 'cabal-version: >= 1.10' must specify the 'default-language' field for each component (e.g. Haskell98 or Haskell2010). If a component uses different languages in different modules then list the other ones in the 'other-languages' field. Preprocessing library for cryptohash-sha256-0.11.101.0.. Building library for cryptohash-sha256-0.11.101.0.. [1 of 2] Compiling Crypto.Hash.SHA256.FFI ( src/Crypto/Hash/SHA256/FFI.hs, dist/build/Crypto/Hash/SHA256/FFI.o ) /usr/bin/ld: -r and -pie may not be used together collect2: error: ld returned 1 exit status cabal: Failed to build cryptohash-sha256-0.11.101.0 (which is required by test:unit-tests from cabal-install-3.3.0.0, test:solver-quickcheck from cabal-install-3.3.0.0 and others). See the build log above for details. ```

[m-renaud]

Looks like a poor interaction between OverloadedStrings and ghc 7.10.3.

[phadej]

I added changelog and merged (squashed) as 10051c3