Fix completion for qualified import

Author: xsebek

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

@@ -65,6 +65,7 @@ import           Language.LSP.Types.Capabilities
 import qualified Language.LSP.VFS                         as VFS
 import           Text.Fuzzy.Parallel                      (Scored (score),
                                                            original)
+import Safe (fromJustNote)
 
 -- Chunk size used for parallelizing fuzzy matching
 chunkSize :: Int
@@ -636,6 +637,8 @@ getCompletions plId ideOpts CC {allModNamesAsNS, anyQualCompls, unqualCompls, qu
         , enteredQual `T.isPrefixOf` original label
         ]
 
+      getModuleName line = let ws = filter (/= "qualified") (T.words line)
+                            in if List.length ws >= 2 then Just (ws !! 1) else Nothing
       filtImportCompls = filtListWith (mkImportCompl enteredQual) importableModules
       filterModuleExports moduleName = filtListWith $ mkModuleFunctionImport moduleName
       filtKeywordCompls
@@ -645,10 +648,10 @@ getCompletions plId ideOpts CC {allModNamesAsNS, anyQualCompls, unqualCompls, qu
   if
     -- TODO: handle multiline imports
     | "import " `T.isPrefixOf` fullLine
-      && (List.length (words (T.unpack fullLine)) >= 2)
-      && "(" `isInfixOf` T.unpack fullLine
+      && isJust (getModuleName fullLine)
+      && "(" `T.isInfixOf` fullLine
     -> do
-      let moduleName = T.pack $ words (T.unpack fullLine) !! 1
+      let moduleName = fromJustNote "NEVER FAILS: module name checked above" $ getModuleName fullLine
           funcs = HM.lookupDefault HashSet.empty moduleName moduleExportsMap
           funs = map (show . name) $ HashSet.toList funcs
       return $ filterModuleExports moduleName $ map T.pack funs

ghcide/test/exe/Main.hs

@@ -5077,8 +5077,8 @@ nonLocalCompletionTests =
             "join"
             ["{-# LANGUAGE NoImplicitPrelude #-}",
             "module A where", "import Control.Monad as M ()", "import Control.Monad as N (join)", "f = N.joi"]
-        -- Failing test for https://github.com/haskell/haskell-language-server/issues/2824
-        , expectFailBecause "known broken #2824" $ completionNoCommandTest
+        -- Regression test for https://github.com/haskell/haskell-language-server/issues/2824
+        , completionNoCommandTest
             "explicit qualified"
             ["{-# LANGUAGE NoImplicitPrelude #-}",
             "module A where", "import qualified Control.Monad as M (j)"]