Refactor completion for cabal files

Add completer function which can be used to complete different types of values inside a cabal file

Author: VeryMilkyJoe

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

@@ -61,6 +61,7 @@ library
     , text
     , text-rope
     , unordered-containers  >=0.2.10.0
+    , haskeline
 
   hs-source-dirs:   src
   default-language: Haskell2010
@@ -82,3 +83,4 @@ test-suite tests
     , lsp-types
     , tasty-hunit
     , text
+

plugins/hls-cabal-plugin/src/Ide/Plugin/Cabal.hs

@@ -275,18 +275,16 @@ completion _ide _ complParams = do
   fmap (Right . J.InL) $ case (contents, uriToFilePath' uri) of
     (Just cnts, Just _path) -> do
       pref <- VFS.getCompletionPrefix position cnts
-      return $ result pref cnts
+      liftIO $ result pref cnts
     _ -> return $ J.List []
   where
-    result :: Maybe VFS.PosPrefixInfo -> VirtualFile -> J.List CompletionItem
-    result Nothing _ = J.List []
+    result :: Maybe VFS.PosPrefixInfo -> VirtualFile -> IO (J.List CompletionItem)
+    result Nothing _ = pure $ J.List []
     result (Just pfix) cnts
-      | pos ^. JL.line == 0 = case context of
-          Just (_, kw)
-            | KeyWord _ <- kw -> J.List $ map buildCompletion $ snd cabalVersionKeyword
-          _ -> J.List [buildCompletion (fst cabalVersionKeyword)]
-      | Just ctx <- context  = J.List $ makeCompletionItems pfix (getCompletionsForContext ctx)
-      | otherwise = J.List []
+      | Just ctx <- context  = do
+        completions <- contextToCompleter ctx
+        pure $ J.List $ makeCompletionItems pfix completions
+      | otherwise = pure $ J.List []
       where
         pos = VFS.cursorPos pfix
         context = getContext pos (Rope.lines $ cnts ^. VFS.file_text)