Ensure eval plugin Print class doesn't rely on Prelude being in scope (#1587)

Author: akrmn

plugins/hls-eval-plugin/src/Ide/Plugin/Eval/Code.hs

@@ -10,15 +10,15 @@ import qualified Data.List.NonEmpty             as NE
 import           Data.String                    (IsString)
 import qualified Data.Text                      as T
 import           Development.IDE.Types.Location (Position (..), Range (..))
-import           GHC                            (compileExpr)
+import           GHC                            (InteractiveImport (IIDecl), compileExpr)
 import           GHC.LanguageExtensions.Type    (Extension (..))
 import           GhcMonad                       (Ghc, GhcMonad, liftIO)
 import           Ide.Plugin.Eval.Types          (Language (Plain), Loc,
                                                  Located (..),
                                                  Section (sectionLanguage),
                                                  Test (..), Txt, locate,
                                                  locate0)
-import           InteractiveEval                (runDecls)
+import           InteractiveEval                (getContext, parseImportDecl, runDecls, setContext)
 import           Language.LSP.Types.Lens        (line, start)
 import           Unsafe.Coerce                  (unsafeCoerce)
 
@@ -95,12 +95,15 @@ evalExtensions =
 
 -- |GHC declarations required for expression evaluation
 evalSetup :: Ghc ()
-evalSetup =
+evalSetup = do
+    preludeAsP <- parseImportDecl "import qualified Prelude as P"
+    context <- getContext
+    setContext (IIDecl preludeAsP : context)
     mapM_
         runDecls
-        [ "class Print f where asPrint :: f -> IO String"
-        , "instance Show a => Print (IO a) where asPrint io = io >>= return . show"
-        , "instance Show a => Print a where asPrint a = return (show a)"
+        [ "class Print f where asPrint :: f -> P.IO P.String"
+        , "instance P.Show a => Print (P.IO a) where asPrint io = io P.>>= P.return P.. P.show"
+        , "instance P.Show a => Print a where asPrint a = P.return (P.show a)"
         ]
 
 {- |GHC declarations required to execute test properties

plugins/hls-eval-plugin/test/Eval.hs

@@ -155,6 +155,8 @@ tests =
                 $ testCase "Literate Haskell Bird Style" $ goldenTest "TLHS.lhs"
             -- , testCase "Literate Haskell LaTeX Style" $ goldenTest "TLHSLateX.lhs"
             ]
+        , testCase "Works with NoImplicitPrelude"
+            $ goldenTest "TNoImplicitPrelude.hs"
         ]
 
 goldenTest :: FilePath -> IO ()

plugins/hls-eval-plugin/test/testdata/TNoImplicitPrelude.hs

@@ -0,0 +1,10 @@
+{-# LANGUAGE NoImplicitPrelude #-}
+
+module TNoImplicitPrelude where
+
+import Data.List (unwords)
+import Data.String (String)
+
+-- >>> unwords example
+example :: [String]
+example = ["This","is","an","example","of","evaluation"]

plugins/hls-eval-plugin/test/testdata/TNoImplicitPrelude.hs.expected

@@ -0,0 +1,11 @@
+{-# LANGUAGE NoImplicitPrelude #-}
+
+module TNoImplicitPrelude where
+
+import Data.List (unwords)
+import Data.String (String)
+
+-- >>> unwords example
+-- "This is an example of evaluation"
+example :: [String]
+example = ["This","is","an","example","of","evaluation"]