Use ghc-lib-parser rather than haskell-src-exts

This patch swaps out the parsing library from `haskell-src-exts` to
`ghc-lib-parser`, which gives us better compatibility with GHC.

Because almost every module heavily used the Haskell AST provided by
`haskell-src-exts`, this was a huge effort and it would not have been possible
without Felix Mulder doing an initial port, GSoC student Beatrice Vergani
porting several other steps, and Łukasz Gołębiewski and Paweł Szulc who helped
me finish up things in the home stretch.

I've generally tried to keep styling 100% compatible with what was there before,
but some issues may have unintentionally slipped in so please report those.

This introduces one new import styling contributed by Felix: when wrapping
import lists over multiple lines, you can repeat the module name, e.g.:

    import Control.Monad.Except as X (ExceptT (..), MonadError (..), liftEither)
    import Control.Monad.Except as X (runExceptT, withExceptT)

This is activated by using `import_align: repeat`.

Secondly, a new Step was added, `module_header`, which formats the export list
of a module, including the trailing `where` clause.  Details for this new step
can be found in the `data/stylish-haskell.yaml`.

Co-Authored-By: Beatrice Vergani <beatrice.vergani11@gmail.com>
Co-Authored-By: Paweł Szulc <paul.szulc@gmail.com>
Co-Authored-By: Łukasz Gołębiewski <lukasz.golebiewski@gmail.com>
Co-Authored-By: Felix Mulder <felix.mulder@klarna.com>

1 files changed, 59 insertions, 0 deletions

diff --git a/data/stylish-haskell.yaml b/data/stylish-haskell.yaml
index d7de260..80892dc 100644
--- a/data/stylish-haskell.yaml
+++ b/data/stylish-haskell.yaml
@@ -15,6 +15,19 @@ steps:
   #     # true.
   #     add_language_pragma: true
 
+  # Format module header
+  #
+  # Currently, this option is not configurable and will format all exports and
+  # module declarations to minimize diffs
+  #
+  # - module_header:
+  #     # How many spaces use for indentation in the module header.
+  #     indent: 4
+  #
+  #     # Should export lists be sorted?  Sorting is only performed within the
+  #     # export section, as delineated by Haddock comments.
+  #     sort: true
+
   # Format record definitions. This is disabled by default.
   #
   # You can control the layout of record fields. The only rules that can't be configured
@@ -42,6 +55,31 @@ steps:
   #
   #     # How many spaces to insert before "deriving" clause. Deriving clauses are always on separate lines.
   #     deriving: 2
+  #
+  #     # How many spaces to insert before "via" clause counted from indentation of deriving clause
+  #     # Possible values:
+  #     # - "same_line" -- "{" and first field goes on the same line as the data constructor.
+  #     # - "indent N" -- insert a new line and N spaces from the beginning of the data constructor
+  #     via: "indent 2"
+  #
+  #     # Wheter or not to break enums onto several lines
+  #     #
+  #     # Default: false
+  #     break_enums: false
+  #
+  #     # Whether or not to break single constructor data types before `=` sign
+  #     #
+  #     # Default: true
+  #     break_single_constructors: true
+  #
+  #     # Whether or not to curry constraints on function.
+  #     #
+  #     # E.g: @allValues :: Enum a => Bounded a => Proxy a -> [a]@
+  #     #
+  #     # Instead of @allValues :: (Enum a, Bounded a) => Proxy a -> [a]@
+  #     #
+  #     # Default: false
+  #     curried_context: false
 
   # Align the right hand side of some elements.  This is quite conservative
   # and only applies to statements where each element occupies a single
@@ -101,6 +139,11 @@ steps:
       #   > import qualified Data.List      as List
       #   >     (concat, foldl, foldr, head, init, last, length)
       #
+      # - repeat: Repeat the module name to align the import list.
+      #
+      #   > import qualified Data.List      as List (concat, foldl, foldr, head)
+      #   > import qualified Data.List      as List (init, last, length)
+      #
       # Default: after_alias
       list_align: after_alias
 
@@ -203,6 +246,22 @@ steps:
       # Default: false
       space_surround: false
 
+      # Enabling this argument will use the new GHC lib parse to format imports.
+      #
+      # This currently assumes a few things, it will assume that you want post
+      # qualified imports. It is also not as feature complete as the old
+      # imports formatting.
+      #
+      # It does not remove redundant lines or merge lines. As such, the full
+      # feature scope is still pending.
+      #
+      # It _is_ however, a fine alternative if you are using features that are
+      # not parseable by haskell src extensions and you're comfortable with the
+      # presets.
+      #
+      # Default: false
+      ghc_lib_parser: false
+
   # Language pragmas
   - language_pragmas:
       # We can generate different styles of language pragma lists.