Don't remove existential quantification (#339) (#344)

Don't remove existential quantification (#339). Also don't remove context from data declarations

Author: imuli

.github/workflows/ci.yml

@@ -29,7 +29,7 @@ jobs:
       name: Cache ~/.stack
       with:
         path: ~/.stack
-        key: ${{ runner.os }}-${{ matrix.ghc }}-v7
+        key: ${{ runner.os }}-${{ matrix.ghc }}-v8
 
     - name: Add ~/.local/bin to PATH
       run: echo "$HOME/.local/bin" >> $GITHUB_PATH

lib/Language/Haskell/Stylish/Step/Data.hs

@@ -357,19 +357,15 @@ putConstructor cfg consIndent (L _ cons) = case cons of
     putText "::"
     space
 
-    when (unLocated con_forall) do
-      putText "forall"
-      space
-      sep space (fmap putOutputable $ hsq_explicit con_qvars)
-      dot
-      space
-
+    putForAll con_forall $ hsq_explicit con_qvars
     forM_ con_mb_cxt (putContext cfg . unLocated)
     putType con_res_ty
 
   XConDecl x ->
     noExtCon x
-  ConDeclH98{..} ->
+  ConDeclH98{..} -> do
+    putForAll con_forall con_ex_tvs
+    forM_ con_mb_cxt (putContext cfg . unLocated)
     case con_args of
       InfixCon arg1 arg2 -> do
         putType arg1
@@ -467,6 +463,15 @@ putNewtypeConstructor cfg (L _ cons) = case cons of
       , "GADT encountered in newtype"
       ]
 
+putForAll :: Located Bool -> [Located (HsTyVarBndr GhcPs)] -> P ()
+putForAll forall ex_tvs =
+  when (unLocated forall) do
+    putText "forall"
+    space
+    sep space (fmap putOutputable ex_tvs)
+    dot
+    space
+
 putContext :: Config -> HsContext GhcPs -> P ()
 putContext Config{..} = suffix (space >> putText "=>" >> space) . \case
   [L _ (HsParTy _ tp)] | cCurriedContext ->

tests/Language/Haskell/Stylish/Step/Data/Tests.hs

@@ -71,6 +71,8 @@ tests = testGroup "Language.Haskell.Stylish.Step.Data.Tests"
     , testCase "case 56" case56
     , testCase "case 57" case57
     , testCase "case 58" case58
+    , testCase "case 59" case59
+    , testCase "case 60" case60
     ]
 
 case00 :: Assertion
@@ -1291,6 +1293,22 @@ case58 = expected @=? testStep (step sameIndentStyle) input
 
     expected = input
 
+-- | Don't remove existential quantification
+--
+-- See https://github.com/haskell/stylish-haskell/issues/339
+case59 :: Assertion
+case59 = assertSnippet (step defaultConfig)
+    [ "data Foo = forall (a :: *) . Bar a" ]
+    [ "data Foo = forall (a :: *). Bar a" ]
+
+-- | Don't remove existential quantification
+--
+-- See https://github.com/haskell/stylish-haskell/issues/339
+case60 :: Assertion
+case60 = assertSnippet (step defaultConfig)
+    [ "data Foo = forall a . Bar a" ]
+    [ "data Foo = forall a. Bar a" ]
+
 sameSameStyle :: Config
 sameSameStyle = Config SameLine SameLine 2 2 False True SameLine False True NoMaxColumns