refactor: clarify Scalar type

It now contains the type of the scalar. This way we can discriminate the
void type in a more obvious way.

src/PostgREST/Error.hs

@@ -283,7 +283,7 @@ noRelBetweenHint parent child schema allRels = ("Perhaps you meant '" <>) <$>
 -- to all the overloaded functions' params using the form "param1, param2, param3, ..."
 -- and shows the best match as hint.
 --
--- >>> let procsDesc = [Routine {pdParams = [RoutineParam {ppName="val"}, RoutineParam {ppName="param"}, RoutineParam {ppName="name"}]}, Routine {pdParams = [RoutineParam {ppName="id"}, RoutineParam {ppName="attr"}]}]
+-- >>> let procsDesc = [Function {pdParams = [RoutineParam {ppName="val"}, RoutineParam {ppName="param"}, RoutineParam {ppName="name"}]}, Function {pdParams = [RoutineParam {ppName="id"}, RoutineParam {ppName="attr"}]}]
 --
 -- >>> noRpcHint "api" "test" ["vall", "pqaram", "nam"] procs procsDesc
 -- Just "Perhaps you meant to call the function api.test(name, param, val)"

src/PostgREST/SchemaCache.hs

@@ -247,7 +247,6 @@ decodeFuncs =
                   <*> column HD.text
                   <*> column HD.bool
                   <*> column HD.bool
-                  <*> column HD.bool
                   <*> column HD.bool)
               <*> (parseVolatility <$> column HD.char)
               <*> column HD.bool
@@ -255,16 +254,15 @@ decodeFuncs =
     addKey :: Routine -> (QualifiedIdentifier, Routine)
     addKey pd = (QualifiedIdentifier (pdSchema pd) (pdName pd), pd)
 
-    parseRetType :: Text -> Text -> Bool -> Bool -> Bool -> Bool -> RetType
-    parseRetType schema name isSetOf isComposite isVoid isCompositeAlias
-      | isVoid    = Single $ Scalar True
+    parseRetType :: Text -> Text -> Bool -> Bool -> Bool -> RetType
+    parseRetType schema name isSetOf isComposite isCompositeAlias
       | isSetOf   = SetOf pgType
       | otherwise = Single pgType
       where
         qi = QualifiedIdentifier schema name
         pgType
           | isComposite = Composite qi isCompositeAlias
-          | otherwise   = Scalar False
+          | otherwise   = Scalar qi
 
     parseVolatility :: Char -> FuncVolatility
     parseVolatility v | v == 'i' = Immutable
@@ -339,7 +337,6 @@ funcsSqlQuery pgVer = [q|
      -- if any TABLE, INOUT or OUT arguments present, treat as composite
      or COALESCE(proargmodes::text[] && '{t,b,o}', false)
     ) AS rettype_is_composite,
-    ('void'::regtype = t.oid) AS rettype_is_void,
     bt.oid <> bt.base as rettype_is_composite_alias,
     p.provolatile,
     p.provariadic > 0 as hasvariadic

src/PostgREST/SchemaCache/Routine.hs

@@ -25,7 +25,7 @@ import PostgREST.SchemaCache.Identifiers (QualifiedIdentifier (..),
 import Protolude
 
 data PgType
-  = Scalar Bool -- True if the type is void
+  = Scalar QualifiedIdentifier
   | Composite QualifiedIdentifier Bool -- True if the composite is a domain alias(used to work around a bug in pg 11 and 12, see QueryBuilder.hs)
   deriving (Eq, Ord, Generic, JSON.ToJSON)
 
@@ -72,12 +72,12 @@ type RoutineMap = HM.HashMap QualifiedIdentifier [Routine]
 
 funcReturnsScalar :: Routine -> Bool
 funcReturnsScalar proc = case proc of
-  Function{pdReturnType = Single (Scalar _)} -> True
+  Function{pdReturnType = Single (Scalar{})} -> True
   _                                          -> False
 
 funcReturnsSetOfScalar :: Routine -> Bool
 funcReturnsSetOfScalar proc = case proc of
-  Function{pdReturnType = SetOf (Scalar _)} -> True
+  Function{pdReturnType = SetOf (Scalar{})} -> True
   _                                         -> False
 
 funcReturnsCompositeAlias :: Routine -> Bool
@@ -93,8 +93,8 @@ funcReturnsSingleComposite proc = case proc of
 
 funcReturnsVoid :: Routine -> Bool
 funcReturnsVoid proc = case proc of
-  Function{pdReturnType = Single (Scalar True)} -> True
-  _                                             -> False
+  Function{pdReturnType = Single (Scalar (QualifiedIdentifier "pg_catalog" "void"))} -> True
+  _                                                                                  -> False
 
 funcTableName :: Routine -> Maybe TableName
 funcTableName proc = case pdReturnType proc of