[purs ide] Reads files in TextMode for adding imports (#2850)

The functions provided in System.IO.UTF8 use ByteString's readFile, which uses
https://hackage.haskell.org/package/base-4.9.1.0/docs/System-IO.html#v:openBinaryFile
under the hood, which in turn causes trouble when we treat source files as text
on Windows.

purescript.cabal

@@ -586,6 +586,8 @@ extra-source-files:
       examples/warning/2411.purs
       examples/warning/2542.purs
       examples/warning/CustomWarning.purs
+      examples/warning/CustomWarning2.purs
+      examples/warning/CustomWarning3.purs
       examples/warning/DuplicateExportRef.purs
       examples/warning/DuplicateImport.purs
       examples/warning/DuplicateImportRef.purs

src/Language/PureScript/Ide/Imports.hs

@@ -85,7 +85,7 @@ parseImportsFromFile file = do
 parseImportsFromFile' :: (MonadIO m, MonadError IdeError m) =>
                         FilePath -> m (P.ModuleName, [Text], [Import], [Text])
 parseImportsFromFile' fp = do
-  file <- ideReadFile fp
+  file <- ideReadTextFile fp
   case sliceImportSection (T.lines file) of
     Right res -> pure res
     Left err -> throwError (GeneralError err)

src/Language/PureScript/Ide/Util.hs

@@ -28,6 +28,7 @@ module Language.PureScript.Ide.Util
   , identT
   , opNameT
   , ideReadFile
+  , ideReadTextFile
   , module Language.PureScript.Ide.Logging
   ) where
 
@@ -37,6 +38,7 @@ import           Protolude                           hiding (decodeUtf8,
 import           Control.Lens                        hiding ((&), op)
 import           Data.Aeson
 import qualified Data.Text                           as T
+import qualified Data.Text.IO                        as TIO
 import qualified Data.Text.Lazy                      as TL
 import           Data.Text.Lazy.Encoding             (decodeUtf8, encodeUtf8)
 import qualified Language.PureScript                 as P
@@ -129,10 +131,25 @@ identT = iso P.runIdent P.Ident
 opNameT :: Iso' (P.OpName a) Text
 opNameT = iso P.runOpName P.OpName
 
-ideReadFile :: (MonadIO m, MonadError IdeError m) => FilePath -> m Text
-ideReadFile fp = do
-  contents :: Either IOException Text <- liftIO (try (readUTF8FileT fp))
+ideReadFile'
+  :: (MonadIO m, MonadError IdeError m)
+  => (FilePath -> IO Text)
+  -> FilePath
+  -> m Text
+ideReadFile' fileReader fp = do
+  contents :: Either IOException Text <- liftIO (try (fileReader fp))
   either
     (\_ -> throwError (GeneralError ("Couldn't find file at: " <> T.pack fp)))
     pure
     contents
+
+ideReadFile :: (MonadIO m, MonadError IdeError m) => FilePath -> m Text
+ideReadFile = ideReadFile' readUTF8FileT
+
+-- | This function is to be used over @ideReadFile@ when the result is not just
+-- passed on to the PureScript parser, but also needs to be treated as lines of
+-- text. Because @ideReadFile@ reads the file as ByteString in @BinaryMode@
+-- rather than @TextMode@ line endings get mangled on Windows otherwise. This is
+-- irrelevant for parsing, because the Lexer strips these additional @\r@'s.
+ideReadTextFile :: (MonadIO m, MonadError IdeError m) => FilePath -> m Text
+ideReadTextFile = ideReadFile' TIO.readFile