dhall format: Strip trailing whitespace

[ocharles]

This uses Data.Text.Prettyprint.Doc.removeTrailingWhitespace to remove
trailing whitespace from pretty printed documents.

In the process I also refactored this module a bit to remove duplication.

Fixes #183.

[ocharles]

Note that this is not ready to be merged as it removes blank lines. Working with @quchen on seeing where the problem is.

prettyprinter-1.3.0 is now out with the fix 🎉

[ocharles]

Looks like we need to wait until hnix supports prettyprinter-1.3.0 now.

[Gabriella439]

Feel free to jailbreak hnix if it's just a bounds failure that is blocking this. dhall-to-nix isn't Hackage-ready yet anyway (until hnix cuts a new Hackage release) since dhall-to-nix currently depends on a git revision of hnix

[ocharles]

Ok, if you're happy with that I'll jailbreak 👍

[quchen]

I thought about which version number to bump, but the Pretty [a] instance does observably change output, so tests like tasty-golden are in danger of breaking.

[Gabriella439]

@quchen: Don't worry about it 🙂

[Gabriella439]

@ocharles: If you merge ocharles#3 into your branch it should at least fix the Nix build failures

[Gabriella439]

Actually, I noticed something odd while using this branch for unrelated reasons. It appears to mess up formatting and color codes.

For example, on master, the following expression:

{ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa = 1, bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb = 2, cccccccccccccccccccccccccccccccccc = 3 }

... is formatted as:

{ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa =
    1
, bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb =
    2
, cccccccccccccccccccccccccccccccccc =
    3
}

... with syntax highlighting. But on this branch the highlighting is gone and it's formatted as:

{ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa =
1
, bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb =
2
, cccccccccccccccccccccccccccccccccc =
3
}

You'll see similar behavior for unions, too.

[sjakobi]

I've started working on a patch that will supersede this PR.

[sjakobi]

@Gabriel439 The missing colors are probably due to the unAnnotateS in prettyExprSource.

The removal of leading whitespace seems to be bug in a prettyprinter: See quchen/prettyprinter#84.

[sjakobi]

Closing in favour of #1422.