Makes local record field completion respects the fields sharing one single type signature

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

@@ -20,7 +20,6 @@ import           Data.List.Extra                          as List hiding
 import qualified Data.Map                                 as Map
 
 import           Data.Maybe                               (fromMaybe, isJust,
-                                                           listToMaybe,
                                                            mapMaybe)
 import qualified Data.Text                                as T
 import qualified Text.Fuzzy.Parallel                      as Fuzzy
@@ -480,7 +479,7 @@ findRecordCompl uri pmod mn DataDecl {tcdLName, tcdDataDefn} = result
                         (showGhc . unLoc $ con_name) field_labels mn doc Nothing
                  | ConDeclH98{..} <- unLoc <$> dd_cons tcdDataDefn
                  , Just  con_details <- [getFlds con_args]
-                 , let field_names = mapMaybe extract con_details
+                 , let field_names = concatMap extract con_details
                  , let field_labels = showGhc . unLoc <$> field_names
                  , (not . List.null) field_labels
                  ]
@@ -493,11 +492,18 @@ findRecordCompl uri pmod mn DataDecl {tcdLName, tcdDataDefn} = result
                              _           -> Nothing
 
         extract ConDeclField{..}
-             -- TODO: Why is cd_fld_names a list?
-            | Just fld_name <- rdrNameFieldOcc . unLoc <$> listToMaybe cd_fld_names = Just fld_name
-            | otherwise = Nothing
+            -- NOTE: 'cd_fld_names' is grouped so that the fields
+            -- sharing the same type declaration to fit in the same group; e.g.
+            --
+            -- @
+            --   data Foo = Foo {arg1, arg2 :: Int, arg3 :: Int, arg4 :: Bool}
+            -- @
+            --
+            -- is encoded as @[[arg1, arg2], [arg3], [arg4]]@
+            -- Hence, we must concat nested arguments into one to get all the fields.
+            = map (rdrNameFieldOcc . unLoc) cd_fld_names
         -- XConDeclField
-        extract _ = Nothing
+        extract _ = []
 findRecordCompl _ _ _ _ = []
 
 ppr :: Outputable a => a -> T.Text

test/functional/Completion.hs

@@ -94,7 +94,6 @@ tests = testGroup "completions" [
          liftIO $ do
              item ^. label @?= "accessor"
              item ^. kind @?= Just CiFunction
-
      , testCase "have implicit foralls on basic polymorphic types" $ runSession hlsCommand fullCaps "test/testdata/completion" $ do
          doc <- openDoc "Completion.hs" "haskell"
 
@@ -261,6 +260,17 @@ snippetTests = testGroup "snippets" [
         doc <- openDoc "Completion.hs" "haskell"
 
         checkNoSnippets doc
+    , testCase "works for record fields sharing the single signature" $ runSession hlsCommand fullCaps "test/testdata/completion" $ do
+         doc <- openDoc "FieldsSharingSignature.hs" "haskell"
+
+         let te = TextEdit (Range (Position 1 0) (Position 1 2)) "MkF"
+         _ <- applyEdit doc te
+
+         compls <- getCompletions doc (Position 1 6)
+         let item = head $ filter (\c -> (c ^. label == "MkFoo") && maybe False ("MkFoo {" `T.isPrefixOf`) (c ^. insertText)) compls
+         liftIO $ do
+            item ^. insertTextFormat @?= Just Snippet
+            item ^. insertText @?= Just "MkFoo {arg1=${1:_arg1}, arg2=${2:_arg2}, arg3=${3:_arg3}, arg4=${4:_arg4}, arg5=${5:_arg5}}"
     ]
     where
         checkNoSnippets doc = do

test/testdata/completion/FieldsSharingSignature.hs

@@ -0,0 +1 @@
+data Foo = MkFoo { arg1, arg2, arg3 :: Int, arg4 :: Int, arg5 :: Double }

test/testdata/completion/hie.yaml

@@ -4,3 +4,4 @@ cradle:
       - "Completion"
       - "Context"
       - "DupRecFields"
+      - "FieldsSharingSignature"