Bracketing for snippet completions

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

@@ -60,6 +60,7 @@ import           Language.LSP.Types
 import           Language.LSP.Types.Capabilities
 import qualified Language.LSP.VFS                         as VFS
 import           Outputable                               (Outputable)
+import           TyCoRep
 
 -- From haskell-ide-engine/hie-plugin-api/Haskell/Ide/Engine/Context.hs
 
@@ -247,9 +248,16 @@ mkNameCompItem doc thingParent origName origMod thingType isInfix docs !imp = CI
       where
         argTypes = getArgs typ
         argText :: T.Text
-        argText =  mconcat $ List.intersperse " " $ zipWithFrom snippet 1 argTypes
+        argText = mconcat $ List.intersperse " " $ zipWithFrom snippet 1 argTypes
         snippet :: Int -> Type -> T.Text
-        snippet i t = "${" <> T.pack (show i) <> ":" <> showGhc t <> "}"
+        snippet i t = case t of
+            (TyVarTy _)     -> noParensSnippet
+            (LitTy _)       -> noParensSnippet
+            (TyConApp _ []) -> noParensSnippet
+            _               -> snippetText i (T.pack "(" <> showGhc t <> T.pack ")")
+            where
+                noParensSnippet = snippetText i (showGhc t)
+                snippetText i t = "${" <> T.pack (show i) <> ":" <> t <> "}"
         getArgs :: Type -> [Type]
         getArgs t
           | isPredTy t = []

ghcide/test/exe/Main.hs

@@ -3900,7 +3900,7 @@ nonLocalCompletionTests =
       "variable"
       ["module A where", "f = hea"]
       (Position 1 7)
-      [("head", CiFunction, "head ${1:[a]}", True, True, Nothing)],
+      [("head", CiFunction, "head ${1:([a])}", True, True, Nothing)],
     completionTest
       "constructor"
       ["module A where", "f = Tru"]
@@ -3912,20 +3912,20 @@ nonLocalCompletionTests =
       "type"
       ["{-# OPTIONS_GHC -Wall #-}", "module A () where", "f :: Bo", "f = True"]
       (Position 2 7)
-      [ ("Bounded", CiInterface, "Bounded ${1:*}", True, True, Nothing),
+      [ ("Bounded", CiInterface, "Bounded ${1:(*)}", True, True, Nothing),
         ("Bool", CiStruct, "Bool ", True, True, Nothing)
       ],
     completionTest
       "qualified"
       ["{-# OPTIONS_GHC -Wunused-binds #-}", "module A () where", "f = Prelude.hea"]
       (Position 2 15)
-      [ ("head", CiFunction, "head ${1:[a]}", True, True, Nothing)
+      [ ("head", CiFunction, "head ${1:([a])}", True, True, Nothing)
       ],
     completionTest
       "duplicate import"
       ["module A where", "import Data.List", "import Data.List", "f = perm"]
       (Position 3 8)
-      [ ("permutations", CiFunction, "permutations ${1:[a]}", False, False, Nothing)
+      [ ("permutations", CiFunction, "permutations ${1:([a])}", False, False, Nothing)
       ],
     completionTest
        "dont show hidden items"

test/functional/Completion.hs

@@ -253,7 +253,7 @@ snippetTests = testGroup "snippets" [
             item ^. label @?= "foldl"
             item ^. kind @?= Just CiFunction
             item ^. insertTextFormat @?= Just Snippet
-            item ^. insertText @?= Just "foldl ${1:b -> a -> b} ${2:b} ${3:t a}"
+            item ^. insertText @?= Just "foldl ${1:(b -> a -> b)} ${2:b} ${3:(t a)}"
 
     , testCase "work for complex types" $ runSession hlsCommand fullCaps "test/testdata/completion" $ do
         doc <- openDoc "Completion.hs" "haskell"
@@ -267,7 +267,7 @@ snippetTests = testGroup "snippets" [
             item ^. label @?= "mapM"
             item ^. kind @?= Just CiFunction
             item ^. insertTextFormat @?= Just Snippet
-            item ^. insertText @?= Just "mapM ${1:a -> m b} ${2:t a}"
+            item ^. insertText @?= Just "mapM ${1:(a -> m b)} ${2:(t a)}"
 
     , testCase "work for infix functions" $ runSession hlsCommand fullCaps "test/testdata/completion" $ do
         doc <- openDoc "Completion.hs" "haskell"