Remove Strict from the language extensions used for code actions (#638)

Since the code action for language extension suggestions uses substring
matching, the presence of the literal name of an extension can trigger
a false positive.

`Strict` is an identifier that occurs frequently in imports, causing
the extension to be suggested rather than the removal of a redundant
import.

Author: tek

src/Development/IDE/Plugin/CodeAction.hs

@@ -266,7 +266,11 @@ suggestAddExtension Diagnostic{_range=_range,..}
 
 -- | All the GHC extensions
 ghcExtensions :: Map.HashMap T.Text Extension
-ghcExtensions = Map.fromList . map ( ( T.pack . flagSpecName ) &&& flagSpecFlag ) $ xFlags
+ghcExtensions = Map.fromList . filter notStrictFlag . map ( ( T.pack . flagSpecName ) &&& flagSpecFlag ) $ xFlags
+  where
+    -- Strict often causes false positives, as in Data.Map.Strict imports.
+    -- See discussion at https://github.com/digital-asset/ghcide/pull/638
+    notStrictFlag (name, _) = name /= "Strict"
 
 suggestModuleTypo :: Diagnostic -> [(T.Text, [TextEdit])]
 suggestModuleTypo Diagnostic{_range=_range,..}

test/exe/Main.hs

@@ -818,6 +818,28 @@ removeImportTests = testGroup "remove import actions"
             , "main = B"
             ]
       liftIO $ expectedContentAfterAction @=? contentAfterAction
+  , testSession "import containing the identifier Strict" $ do
+      let contentA = T.unlines
+            [ "module Strict where"
+            ]
+      _docA <- createDoc "Strict.hs" "haskell" contentA
+      let contentB = T.unlines
+            [ "{-# OPTIONS_GHC -Wunused-imports #-}"
+            , "module ModuleB where"
+            , "import Strict"
+            ]
+      docB <- createDoc "ModuleB.hs" "haskell" contentB
+      _ <- waitForDiagnostics
+      [CACodeAction action@CodeAction { _title = actionTitle }]
+          <- getCodeActions docB (Range (Position 2 0) (Position 2 5))
+      liftIO $ "Remove import" @=? actionTitle
+      executeCodeAction action
+      contentAfterAction <- documentContents docB
+      let expectedContentAfterAction = T.unlines
+            [ "{-# OPTIONS_GHC -Wunused-imports #-}"
+            , "module ModuleB where"
+            ]
+      liftIO $ expectedContentAfterAction @=? contentAfterAction
   ]
 
 extendImportTests :: TestTree