Suggest imports without the parent class

When suggesting to import a method `m` of class `C` from module `M`, in addition
to the suggestions `import M` and `import M (C(m))`, also suggest importing the
method without mentioning the enclosing class: `import M (m)`.

Author: mrBliss

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

@@ -48,6 +48,8 @@ import Data.Aeson.Types (toJSON, fromJSON, Value(..), Result(..))
 import Data.Char
 import Data.Maybe
 import Data.List.Extra
+import Data.List.NonEmpty (NonEmpty((:|)))
+import qualified Data.List.NonEmpty as NE
 import qualified Data.Text as T
 import Text.Regex.TDFA (mrAfter, (=~), (=~~))
 import Outputable (ppr, showSDocUnsafe)
@@ -620,9 +622,13 @@ suggestExtendImport exportsMap contents Diagnostic{_range=_range,..}
                    in x{_end = (_end x){_character = succ (_character (_end x))}}
                 _ -> error "bug in srcspan parser",
             importLine <- textInRange range c,
-            Just ident <- lookupExportMap binding mod,
-            Just result <- addBindingToImportList ident importLine
-            = [("Add " <> renderIdentInfo ident <> " to the import list of " <> mod, [TextEdit range result])]
+            Just ident <- lookupExportMap binding mod
+          = [ ( "Add " <> rendered <> " to the import list of " <> mod
+              , [TextEdit range result]
+              )
+            | importStyle <- NE.toList $ importStyles ident
+            , let rendered = renderImportStyle importStyle
+            , result <- maybeToList $ addBindingToImportList importStyle importLine]
           | otherwise = []
         lookupExportMap binding mod
           | Just match <- Map.lookup binding (getExportsMap exportsMap)
@@ -931,13 +937,15 @@ constructNewImportSuggestions exportsMap (qual, thingMissing) notTheseModules =
   , suggestion <- renderNewImport identInfo m
   ]
  where
+  renderNewImport :: IdentInfo -> T.Text -> [T.Text]
   renderNewImport identInfo m
     | Just q <- qual
     , asQ <- if q == m then "" else " as " <> q
     = ["import qualified " <> m <> asQ]
     | otherwise
-    = ["import " <> m <> " (" <> renderIdentInfo identInfo <> ")"
-      ,"import " <> m ]
+    = ["import " <> m <> " (" <> renderImportStyle importStyle <> ")"
+      | importStyle <- NE.toList $ importStyles identInfo] ++
+      ["import " <> m ]
 
 canUseIdent :: NotInScope -> IdentInfo -> Bool
 canUseIdent NotInScopeDataConstructor{} = isDatacon
@@ -1078,15 +1086,18 @@ rangesForBinding' _ _ = []
 --       import (qualified) A (..) ..
 --   Places the new binding first, preserving whitespace.
 --   Copes with multi-line import lists
-addBindingToImportList :: IdentInfo -> T.Text -> Maybe T.Text
-addBindingToImportList IdentInfo {parent = _parent, ..} importLine =
+addBindingToImportList :: ImportStyle -> T.Text -> Maybe T.Text
+addBindingToImportList importStyle importLine =
   case T.breakOn "(" importLine of
     (pre, T.uncons -> Just (_, rest)) ->
-      case _parent of
-        -- the binding is not a constructor, add it to the head of import list
-        Nothing -> Just $ T.concat [pre, "(", rendered, addCommaIfNeeds rest]
-        Just parent -> case T.breakOn parent rest of
-          -- the binding is a constructor, and current import list contains its parent
+      case importStyle of
+        ImportTopLevel rendered ->
+          -- the binding has no parent, add it to the head of import list
+          Just $ T.concat [pre, "(", rendered, addCommaIfNeeds rest]
+        ImportViaParent rendered parent -> case T.breakOn parent rest of
+          -- the binding has a parent, and the current import list contains the
+          -- parent
+          --
           -- `rest'` could be 1. `,...)`
           --               or 2. `(),...)`
           --               or 3. `(ConsA),...)`
@@ -1178,7 +1189,43 @@ matchRegExMultipleImports message = do
   imps <- regExImports imports
   return (binding, imps)
 
-renderIdentInfo :: IdentInfo -> T.Text
-renderIdentInfo IdentInfo {parent, rendered}
-  | Just p <- parent = p <> "(" <> rendered <> ")"
-  | otherwise        = rendered
+-- | Possible import styles for an 'IdentInfo'.
+--
+-- The first 'Text' parameter corresponds to the 'rendered' field of the
+-- 'IdentInfo'.
+data ImportStyle
+    = ImportTopLevel T.Text
+      -- ^ Import a top-level export from a module, e.g., a function, a type, a
+      -- class.
+      --
+      -- > import M (?)
+      --
+      -- Some exports that have a parent, like a type-class method or an
+      -- associated type/data family, can still be imported as a top-level
+      -- import.
+      --
+      -- Note that this is not the case for constructors, they must always be
+      -- imported as part of their parent data type.
+
+    | ImportViaParent T.Text T.Text
+      -- ^ Import an export (first parameter) through its parent (second
+      -- parameter).
+      --
+      -- import M (P(?))
+      --
+      -- @P@ and @?@ can be a data type and a constructor, a class and a method,
+      -- a class and an associated type/data family, etc.
+
+importStyles :: IdentInfo -> NonEmpty ImportStyle
+importStyles IdentInfo {parent, rendered, isDatacon}
+  | Just p <- parent
+    -- Constructors always have to be imported via their parent data type, but
+    -- methods and associated type/data families can also be imported as
+    -- top-level exports.
+  = ImportViaParent rendered p :| [ImportTopLevel rendered | not isDatacon]
+  | otherwise
+  = ImportTopLevel rendered :| []
+
+renderImportStyle :: ImportStyle -> T.Text
+renderImportStyle (ImportTopLevel x) = x
+renderImportStyle (ImportViaParent x p) = p <> "(" <> x <> ")"

ghcide/src/Development/IDE/Types/Exports.hs

@@ -53,15 +53,15 @@ mkIdentInfos (Avail n) =
 mkIdentInfos (AvailTC parent (n:nn) flds)
     -- Following the GHC convention that parent == n if parent is exported
     | n == parent
-    = [ IdentInfo (pack (prettyPrint n)) (pack (printName n)) (Just $! parentP) True
+    = [ IdentInfo (pack (prettyPrint n)) (pack (printName n)) (Just $! parentP) (isDataConName n)
         | n <- nn ++ map flSelector flds
       ] ++
-      [ IdentInfo (pack (prettyPrint n)) (pack (printName n)) Nothing False]
+      [ IdentInfo (pack (prettyPrint n)) (pack (printName n)) Nothing (isDataConName n)]
     where
         parentP = pack $ prettyPrint parent
 
 mkIdentInfos (AvailTC _ nn flds)
-    = [ IdentInfo (pack (prettyPrint n)) (pack (printName n)) Nothing True
+    = [ IdentInfo (pack (prettyPrint n)) (pack (printName n)) Nothing (isDataConName n)
         | n <- nn ++ map flSelector flds
       ]
 

ghcide/test/exe/Main.hs

@@ -1207,6 +1207,46 @@ extendImportTests = testGroup "extend import actions"
                     , "               )"
                     , "main = print (stuffA, stuffB)"
                     ])
+        , testSession "extend single line import with method within class" $ template
+            [("ModuleA.hs", T.unlines
+                    [ "module ModuleA where"
+                    , "class C a where"
+                    , "  m1 :: a -> a"
+                    , "  m2 :: a -> a"
+                    ])]
+            ("ModuleB.hs", T.unlines
+                    [ "module ModuleB where"
+                    , "import ModuleA (C(m1))"
+                    , "b = m2"
+                    ])
+            (Range (Position 2 5) (Position 2 5))
+            ["Add C(m2) to the import list of ModuleA",
+             "Add m2 to the import list of ModuleA"]
+            (T.unlines
+                    [ "module ModuleB where"
+                    , "import ModuleA (C(m2, m1))"
+                    , "b = m2"
+                    ])
+        , testSession "extend single line import with method without class" $ template
+            [("ModuleA.hs", T.unlines
+                    [ "module ModuleA where"
+                    , "class C a where"
+                    , "  m1 :: a -> a"
+                    , "  m2 :: a -> a"
+                    ])]
+            ("ModuleB.hs", T.unlines
+                    [ "module ModuleB where"
+                    , "import ModuleA (C(m1))"
+                    , "b = m2"
+                    ])
+            (Range (Position 2 5) (Position 2 5))
+            ["Add m2 to the import list of ModuleA",
+             "Add C(m2) to the import list of ModuleA"]
+            (T.unlines
+                    [ "module ModuleB where"
+                    , "import ModuleA (m2, C(m1))"
+                    , "b = m2"
+                    ])
         , testSession "extend import list with multiple choices" $ template
             [("ModuleA.hs", T.unlines
                     --  this is just a dummy module to help the arguments needed for this test
@@ -1296,6 +1336,8 @@ suggestImportTests = testGroup "suggest import actions"
     , test False []         "f :: Typeable a => a"        ["f = undefined"] "import Data.Typeable.Internal (Typeable)"
       -- package not in scope
     , test False []         "f = quickCheck"              []                "import Test.QuickCheck (quickCheck)"
+      -- don't omit the parent data type of a constructor
+    , test False []         "f ExitSuccess = ()"          []                "import System.Exit (ExitSuccess)"
     ]
   , testGroup "want suggestion"
     [ wantWait  []          "f = foo"                     []                "import Foo (foo)"
@@ -1316,6 +1358,7 @@ suggestImportTests = testGroup "suggest import actions"
     , test True []          "f :: Alternative f => f ()"  ["f = undefined"] "import Control.Applicative (Alternative)"
     , test True []          "f :: Alternative f => f ()"  ["f = undefined"] "import Control.Applicative"
     , test True []          "f = empty"                   []                "import Control.Applicative (Alternative(empty))"
+    , test True []          "f = empty"                   []                "import Control.Applicative (empty)"
     , test True []          "f = empty"                   []                "import Control.Applicative"
     , test True []          "f = (&)"                     []                "import Data.Function ((&))"
     , test True []          "f = NE.nonEmpty"             []                "import qualified Data.List.NonEmpty as NE"
@@ -1326,6 +1369,7 @@ suggestImportTests = testGroup "suggest import actions"
     , test True []          "f = [] & id"                 []                "import Data.Function ((&))"
     , test True []          "f = (&) [] id"               []                "import Data.Function ((&))"
     , test True []          "f = (.|.)"                   []                "import Data.Bits (Bits((.|.)))"
+    , test True []          "f = (.|.)"                   []                "import Data.Bits ((.|.))"
     ]
   ]
   where