Add an option to run Fourmolu via the CLI interface of a separate binary, rather than the bundled library

This makes it easier to set up an environment (e.g. a Nix shell) which uses the same version of Fourmolu in HLS as from the command line.

It can also be useful when Fourmolu has updated and we don't want to wait a month for an HLS release, or re-compile.

Author: georgefst

hls-plugin-api/src/Ide/Plugin/Config.hs

@@ -50,6 +50,7 @@ data Config =
     { checkParents       :: CheckParents
     , checkProject       :: !Bool
     , formattingProvider :: !T.Text
+    , formattingCLI      :: !Bool
     , maxCompletions     :: !Int
     , plugins            :: !(Map.Map T.Text PluginConfig)
     } deriving (Show,Eq)
@@ -62,6 +63,7 @@ instance Default Config where
     , formattingProvider          = "ormolu"
     -- , formattingProvider          = "floskell"
     -- , formattingProvider          = "stylish-haskell"
+    , formattingCLI               = False
     , maxCompletions              = 40
     , plugins                     = Map.empty
     }
@@ -78,6 +80,7 @@ parseConfig defValue = A.withObject "Config" $ \v -> do
         <$> (o .:? "checkParents" <|> v .:? "checkParents") .!= checkParents defValue
         <*> (o .:? "checkProject" <|> v .:? "checkProject") .!= checkProject defValue
         <*> o .:? "formattingProvider"                      .!= formattingProvider defValue
+        <*> o .:? "formattingCLI"                           .!= formattingCLI defValue
         <*> o .:? "maxCompletions"                          .!= maxCompletions defValue
         <*> o .:? "plugin"                                  .!= plugins defValue
 

plugins/hls-fourmolu-plugin/hls-fourmolu-plugin.cabal

@@ -30,6 +30,7 @@ library
     , hls-plugin-api  ^>=1.3
     , lens
     , lsp
+    , process
     , text
 
   default-language: Haskell2010

plugins/hls-fourmolu-plugin/src/Ide/Plugin/Fourmolu.hs

@@ -8,22 +8,28 @@ module Ide.Plugin.Fourmolu (
     provider,
 ) where
 
-import           Control.Exception               (try)
+import           Control.Exception               (IOException, try)
 import           Control.Lens                    ((^.))
+import           Control.Monad
 import           Control.Monad.IO.Class
 import           Data.Bifunctor                  (first)
+import           Data.Maybe
 import qualified Data.Text                       as T
 import           Development.IDE                 hiding (pluginHandlers)
 import           Development.IDE.GHC.Compat      as Compat hiding (Cpp)
 import qualified Development.IDE.GHC.Compat.Util as S
 import           GHC.LanguageExtensions.Type     (Extension (Cpp))
+import           Ide.Plugin.Config               (formattingCLI)
 import           Ide.PluginUtils                 (makeDiffTextEdit)
 import           Ide.Types
 import           Language.LSP.Server             hiding (defaultConfig)
 import           Language.LSP.Types
 import           Language.LSP.Types.Lens         (HasTabSize (tabSize))
 import           Ormolu
+import           System.Exit
 import           System.FilePath
+import           System.IO                       (stderr, hPutStrLn)
+import           System.Process
 
 -- ---------------------------------------------------------------------
 
@@ -41,7 +47,30 @@ provider ideState typ contents fp fo = withIndefiniteProgress title Cancellable
     fileOpts <- case hsc_dflags . hscEnv <$> ghc of
         Nothing -> return []
         Just df -> liftIO $ convertDynFlags df
-    do
+    useCLI <- formattingCLI <$> getConfig
+    if useCLI
+        then liftIO
+            . fmap (join . first (mkError . show))
+            . try @IOException
+            $ do
+                (exitCode, out, err) <-
+                    readProcessWithExitCode
+                        "fourmolu"
+                        ( ["-d"]
+                            <> catMaybes
+                                [ ("--start-line=" <>) . show <$> regionStartLine region
+                                , ("--end-line=" <>) . show <$> regionEndLine region
+                                ]
+                            <> map ("-o" <>) fileOpts
+                        )
+                        (T.unpack contents)
+                hPutStrLn stderr err
+                case exitCode of
+                    ExitSuccess ->
+                        pure . Right $ makeDiffTextEdit contents $ T.pack out
+                    ExitFailure n ->
+                        pure . Left . responseError $ "Fourmolu failed with exit code " <> T.pack (show n)
+        else do
             let format printerOpts =
                     first (mkError . show)
                         <$> try @OrmoluException (makeDiffTextEdit contents <$> ormolu config fp' (T.unpack contents))