sub_select produces invalid SQL sometimes

.gitignore

@@ -5,3 +5,4 @@ stack.yaml.lock
 .cabal-sandbox/
 cabal.sandbox.config
 .hspec-failures
+stack.yaml.lock

src/Database/Esqueleto/Internal/Internal.hs

@@ -634,11 +634,11 @@ v `notIn` e = ifNotEmptyList e True  $ unsafeSqlBinOp " NOT IN " v (veryUnsafeCo
 -- return person
 -- @
 exists :: SqlQuery () -> SqlExpr (Value Bool)
-exists    = unsafeSqlFunction     "EXISTS " . existsHelper
+exists    = unsafeSqlFunctionNoParens     "EXISTS " . existsHelper
 
 -- | @NOT EXISTS@ operator.
 notExists :: SqlQuery () -> SqlExpr (Value Bool)
-notExists = unsafeSqlFunction "NOT EXISTS " . existsHelper
+notExists = unsafeSqlFunctionNoParens "NOT EXISTS " . existsHelper
 
 -- | @SET@ clause used on @UPDATE@s.  Note that while it's not
 -- a type error to use this function on a @SELECT@, it will
@@ -1717,6 +1717,14 @@ unsafeSqlValue v = ERaw Never $ const (v, mempty)
 unsafeSqlFunction :: UnsafeSqlFunctionArgument a =>
                      TLB.Builder -> a -> SqlExpr (Value b)
 unsafeSqlFunction name arg =
+  ERaw Never $ \info ->
+    let (argsTLB, argsVals) =
+          uncommas' $ map (\(ERaw _ f) -> f info) $ toArgList arg
+    in (name <> parens (parens argsTLB), argsVals)
+
+unsafeSqlFunctionNoParens :: UnsafeSqlFunctionArgument a =>
+                     TLB.Builder -> a -> SqlExpr (Value b)
+unsafeSqlFunctionNoParens name arg =
   ERaw Never $ \info ->
     let (argsTLB, argsVals) =
           uncommas' $ map (\(ERaw _ f) -> f info) $ toArgList arg

test/Common/Test.hs

@@ -219,6 +219,22 @@ testSelect run = do
         ret <- select $ return nothing
         liftIO $ ret `shouldBe` [ Value (Nothing :: Maybe Int) ]
 
+  describe "sub_select" $ do
+    it "works inside of sum" $ do
+      run $ do
+        ret <-
+          select $
+          pure $
+            sum_ $
+              sub_select $
+              from $ \foo -> do
+              pure (foo ^. FooName)
+        nonSub <-
+          select $
+          from $ \foo -> do
+          pure (sum_ (foo ^. FooName))
+
+        liftIO $ ret `shouldBe` (nonSub :: [Value (Maybe Int)])
 
 testSelectSource :: Run -> Spec
 testSelectSource run = do