Remove several outdated backend constraints

## Description

This PR removes as many constraints as possible from Backend without refactoring the code. Thanks to #1844, a few ToJSON functions can be removed from the IR, and several constraints were simply redundant.

This PR borrows from similar work done as part of #1666.

## Note

To remove constraints more aggressively, I have explored the possibility of _removing Representable altogether_, in a [separate commit](https://github.com/hasura/graphql-engine-mono/compare/nicuveo/remove-extension-constraints..nicuveo/tentative-remove-representable). I am not convinced it's a good idea in terms of readability of the code, but it's a possibility.

Further work includes deciding what we want to do with `Show` and `ToTxt`; see #1747.

https://github.com/hasura/graphql-engine-mono/pull/1843

GitOrigin-RevId: 337324ad90cb8f86f06e1c5a36aa44bb414e195a

server/src-lib/Hasura/RQL/IR/BoolExp.hs

@@ -52,7 +52,6 @@ import           Data.Aeson.Internal
 import           Data.Aeson.TH
 import           Data.Monoid
 import           Data.Text.Extended
-import           Data.Typeable                  (Typeable)
 
 import           Hasura.Incremental             (Cacheable)
 import           Hasura.RQL.Types.Backend
@@ -129,7 +128,7 @@ data GExists (b :: BackendType) a
   } deriving (Functor, Foldable, Traversable, Generic)
 deriving instance (Backend b, Show a) => Show (GExists b a)
 deriving instance (Backend b, Eq   a) => Eq   (GExists b a)
-deriving instance (Backend b, Typeable a, Data a) => Data (GExists b a)
+deriving instance (Backend b, Data a) => Data (GExists b a)
 instance (Backend b, NFData    a) => NFData    (GExists b a)
 instance (Backend b, Data      a) => Plated    (GExists b a)
 instance (Backend b, Cacheable a) => Cacheable (GExists b a)
@@ -189,8 +188,7 @@ data PartialSQLExp (b :: BackendType)
   = PSESessVar !(SessionVarType b) !SessionVariable
   | PSESQLExp !(SQLExpression b)
   deriving (Generic)
-deriving instance (Backend b) => Eq   (PartialSQLExp b)
-deriving instance (Backend b) => Data (PartialSQLExp b)
+deriving instance (Backend b) => Eq (PartialSQLExp b)
 instance (Backend b, NFData    (BooleanOperators b (PartialSQLExp b))) => NFData    (PartialSQLExp b)
 instance (Backend b, Cacheable (BooleanOperators b (PartialSQLExp b))) => Hashable  (PartialSQLExp b)
 instance (Backend b, Hashable  (BooleanOperators b (PartialSQLExp b))) => Cacheable (PartialSQLExp b)

server/src-lib/Hasura/RQL/IR/OrderBy.hs

@@ -29,13 +29,6 @@ instance FromJSON OrderByCol where
     (String t) -> orderByColFromToks $ T.split (=='.') t
     v          -> parseJSON v >>= orderByColFromToks
 
-instance ToJSON OrderByCol where
-  toJSON = toJSON . orderByColToTxt
-
-orderByColToTxt :: OrderByCol -> Text
-orderByColToTxt = \case
-  OCPG pgCol      -> getFieldNameTxt pgCol
-  OCRel rel obCol -> getFieldNameTxt rel <> "." <> orderByColToTxt obCol
 
 orderByColFromToks
   :: (MonadFail m)
@@ -70,6 +63,3 @@ deriving instance (Backend b, Eq a)   => Eq   (OrderByItemG b a)
 instance (Backend b, Hashable a) => Hashable (OrderByItemG b a)
 
 type OrderByItem b = OrderByItemG b OrderByCol
-
-instance (Backend b, ToJSON a) => ToJSON (OrderByItemG b a) where
-  toJSON = genericToJSON hasuraJSON{omitNothingFields=True}

server/src-lib/Hasura/RQL/Types/Backend.hs

@@ -16,7 +16,7 @@ import           Hasura.SQL.Tag
 import           Hasura.SQL.Types
 
 
-type Representable a = (Show a, Eq a, Hashable a, Cacheable a, NFData a, Typeable a)
+type Representable a = (Show a, Eq a, Hashable a, Cacheable a, NFData a)
 
 type SessionVarType b = CollectableType (ScalarType b)
 
@@ -53,42 +53,28 @@ class
   , Representable (ScalarType b)
   , Representable (SQLExpression b)
   , Representable (SQLOperator b)
-  , Representable (SessionVarType b)
   , Representable (SourceConnConfiguration b)
   , Representable (ExtraTableMetadata b)
-  , Representable (XRelay b)
-  , Representable (XNodesAgg b)
   , Representable (XComputedField b)
-  , Generic (Column b)
-  , Eq (RawFunctionInfo b)
   , Ord (TableName b)
   , Ord (FunctionName b)
   , Ord (ScalarType b)
-  , Ord (XRelay b)
-  , Ord (Column b)
   , Data (TableName b)
-  , Data (ScalarType b)
   , Traversable (BooleanOperators b)
-  , Data (SQLExpression b)
-  , FromJSON (BasicOrderType b)
   , FromJSON (Column b)
   , FromJSON (ConstraintName b)
   , FromJSON (FunctionName b)
-  , FromJSON (NullsOrderType b)
   , FromJSON (ScalarType b)
   , FromJSON (TableName b)
   , FromJSON (SourceConnConfiguration b)
   , FromJSON (ExtraTableMetadata b)
   , FromJSONKey (Column b)
-  , ToJSON (BasicOrderType b)
   , ToJSON (Column b)
   , ToJSON (ConstraintName b)
   , ToJSON (FunctionArgType b)
   , ToJSON (FunctionName b)
-  , ToJSON (NullsOrderType b)
   , ToJSON (ScalarType b)
   , ToJSON (SourceConfig b)
-  , ToJSON (SourceConfig b)
   , ToJSON (TableName b)
   , ToJSON (SourceConnConfiguration b)
   , ToJSON (ExtraTableMetadata b)
@@ -103,6 +89,8 @@ class
   , ToTxt (TableName b)
   , ToTxt (ConstraintName b)
   , Cacheable (SourceConfig b)
+  , Typeable (TableName b)
+  , Typeable (ConstraintName b)
   , Typeable b
   , HasTag b
   ) => Backend (b :: BackendType) where