Limit completions to top 20

We are overwhelming the LSP client by sending 100s of completions after the
first character. Instead, let's send 20 at a time and refresh for more when the
user types another word

Author: pepeiborra

ghcide/src/Development/IDE/Plugin/Completions.hs

@@ -145,11 +145,19 @@ getCompletionsLSP lsp ide
               (Just pfix', _) -> do
                 let clientCaps = clientCapabilities $ shakeExtras ide
                 snippets <- WithSnippets . completionSnippetsOn <$> getClientConfig lsp
-                Completions . List <$> getCompletions ideOpts cci' parsedMod bindMap pfix' clientCaps snippets
+                allCompletions <- getCompletions ideOpts cci' parsedMod bindMap pfix' clientCaps snippets
+                let topCompletions = List $ take 20 allCompletions
+                    isComplete = allCompletions `longerThan` 20
+                pure $ CompletionList (CompletionListType isComplete topCompletions)
               _ -> return (Completions $ List [])
           _ -> return (Completions $ List [])
       _ -> return (Completions $ List [])
 
+longerThan :: [a] -> Int -> Bool
+longerThan [] _ = False
+longerThan _ 0 = True
+longerThan (_ : aa) n = longerThan aa (n -1)
+
 setHandlersCompletion :: PartialHandlers Config
 setHandlersCompletion = PartialHandlers $ \WithMessage{..} x -> return x{
     LSP.completionHandler = withResponse RspCompletion getCompletionsLSP

ghcide/src/Development/IDE/Plugin/Completions/Logic.hs

@@ -565,9 +565,11 @@ getCompletions ideOpts CC { allModNamesAsNS, unqualCompls, qualCompls, importabl
         = filtPragmaCompls (pragmaSuffix fullLine)
         | otherwise
         = let uniqueFiltCompls = nubOrdOn insertText filtCompls
-          in filtModNameCompls ++ map (toggleSnippets caps withSnippets
-                                         . mkCompl ideOpts . stripAutoGenerated) uniqueFiltCompls
-                               ++ filtKeywordCompls
+          in filtModNameCompls
+          ++ filtKeywordCompls
+          ++ map ( toggleSnippets caps withSnippets
+                 . mkCompl ideOpts . stripAutoGenerated
+                 ) uniqueFiltCompls
   return result