graphql/src/Language/GraphQL/Execute/Transform.hs

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{-# LANGUAGE ExplicitForAll #-}
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{-# LANGUAGE LambdaCase #-}
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{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE TupleSections #-}
-- | After the document is parsed, before getting executed, the AST is
-- transformed into a similar, simpler AST. Performed transformations include:
--
-- * Replacing variables with their values.
-- * Inlining fragments. Some fragments can be completely eliminated and
-- replaced by the selection set they represent. Invalid (recursive and
-- non-existing) fragments are skipped. The most fragments are inlined, so the
-- executor doesn't have to perform additional lookups later.
-- * Evaluating directives (@\@include@ and @\@skip@).
--
-- This module is also responsible for smaller rewrites that touch only parts of
-- the original AST.
module Language.GraphQL.Execute.Transform
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( Document(..)
, Fragment(..)
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, QueryError(..)
, Operation(..)
, Selection(..)
, Field(..)
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, document
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, queryError
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) where
import Control.Monad (foldM, unless)
import Control.Monad.Trans.Class (lift)
import Control.Monad.Trans.State (State, evalStateT, gets, modify)
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import Data.Foldable (find)
import Data.Functor.Identity (Identity(..))
import Data.HashMap.Strict (HashMap)
import qualified Data.HashMap.Strict as HashMap
import Data.Maybe (fromMaybe)
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import Data.List.NonEmpty (NonEmpty(..))
import qualified Data.List.NonEmpty as NonEmpty
import Data.Sequence (Seq, (<|), (><))
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import Data.Text (Text)
import qualified Data.Text as Text
import qualified Language.GraphQL.AST as Full
import Language.GraphQL.AST.Core
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import Language.GraphQL.Execute.Coerce
import qualified Language.GraphQL.Type.Directive as Directive
import Language.GraphQL.Type.Definition (Subs, Value(..))
import qualified Language.GraphQL.AST.Core as Core
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import qualified Language.GraphQL.Type.In as In
import qualified Language.GraphQL.Type.Out as Out
import qualified Language.GraphQL.Type.Directive as Core
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import Language.GraphQL.Type.Schema
-- | Associates a fragment name with a list of 'Core.Field's.
data Replacement m = Replacement
{ fragments :: HashMap Full.Name (Fragment m)
, fragmentDefinitions :: FragmentDefinitions
, variableValues :: Subs
, types :: HashMap Full.Name (Type m)
}
type FragmentDefinitions = HashMap Full.Name Full.FragmentDefinition
-- | Represents fragments and inline fragments.
data Fragment m
= Fragment (CompositeType m) (Seq (Selection m))
-- | Single selection element.
data Selection m
= SelectionFragment (Fragment m)
| SelectionField (Field m)
-- | GraphQL has 3 operation types: queries, mutations and subscribtions.
--
-- Currently only queries and mutations are supported.
data Operation m
= Query (Maybe Text) (Seq (Selection m))
| Mutation (Maybe Text) (Seq (Selection m))
-- | Single GraphQL field.
data Field m = Field (Maybe Full.Name) Full.Name Arguments (Seq (Selection m))
-- | Contains the operation to be executed along with its root type.
data Document m = Document
(HashMap Full.Name (Type m)) (Out.ObjectType m) (Operation m)
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data OperationDefinition = OperationDefinition
Full.OperationType
(Maybe Full.Name)
[Full.VariableDefinition]
[Full.Directive]
Full.SelectionSet
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-- | Query error types.
data QueryError
= OperationNotFound Text
| OperationNameRequired
| CoercionError
| TransformationError
| EmptyDocument
| UnsupportedRootOperation
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queryError :: QueryError -> Text
queryError (OperationNotFound operationName) = Text.unwords
["Operation", operationName, "couldn't be found in the document."]
queryError OperationNameRequired = "Missing operation name."
queryError CoercionError = "Coercion error."
queryError TransformationError = "Schema transformation error."
queryError EmptyDocument =
"The document doesn't contain any executable operations."
queryError UnsupportedRootOperation =
"Root operation type couldn't be found in the schema."
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getOperation
:: Maybe Full.Name
-> NonEmpty OperationDefinition
-> Either QueryError OperationDefinition
getOperation Nothing (operation' :| []) = pure operation'
getOperation Nothing _ = Left OperationNameRequired
getOperation (Just operationName) operations
| Just operation' <- find matchingName operations = pure operation'
| otherwise = Left $ OperationNotFound operationName
where
matchingName (OperationDefinition _ name _ _ _) =
name == Just operationName
lookupInputType
:: Full.Type
-> HashMap.HashMap Full.Name (Type m)
-> Maybe In.Type
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lookupInputType (Full.TypeNamed name) types =
case HashMap.lookup name types of
Just (ScalarType scalarType) ->
Just $ In.NamedScalarType scalarType
Just (EnumType enumType) ->
Just $ In.NamedEnumType enumType
Just (InputObjectType objectType) ->
Just $ In.NamedInputObjectType objectType
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_ -> Nothing
lookupInputType (Full.TypeList list) types
= In.ListType
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<$> lookupInputType list types
lookupInputType (Full.TypeNonNull (Full.NonNullTypeNamed nonNull)) types =
case HashMap.lookup nonNull types of
Just (ScalarType scalarType) ->
Just $ In.NonNullScalarType scalarType
Just (EnumType enumType) ->
Just $ In.NonNullEnumType enumType
Just (InputObjectType objectType) ->
Just $ In.NonNullInputObjectType objectType
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_ -> Nothing
lookupInputType (Full.TypeNonNull (Full.NonNullTypeList nonNull)) types
= In.NonNullListType
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<$> lookupInputType nonNull types
coerceVariableValues :: VariableValue a
=> forall m
. HashMap Full.Name (Type m)
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-> OperationDefinition
-> HashMap.HashMap Full.Name a
-> Either QueryError Subs
coerceVariableValues types operationDefinition variableValues' =
let OperationDefinition _ _ variableDefinitions _ _ = operationDefinition
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in maybe (Left CoercionError) Right
$ foldr coerceValue (Just HashMap.empty) variableDefinitions
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where
coerceValue variableDefinition coercedValues = do
let Full.VariableDefinition variableName variableTypeName defaultValue =
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variableDefinition
let defaultValue' = constValue <$> defaultValue
let value' = HashMap.lookup variableName variableValues'
variableType <- lookupInputType variableTypeName types
HashMap.insert variableName
<$> choose value' defaultValue' variableType
<*> coercedValues
choose Nothing defaultValue variableType
| Just _ <- defaultValue = defaultValue
| not (In.isNonNullType variableType) = Just Null
choose (Just value') _ variableType
| Just coercedValue <- coerceVariableValue variableType value'
, not (In.isNonNullType variableType) || coercedValue /= Null =
Just coercedValue
choose _ _ _ = Nothing
constValue :: Full.ConstValue -> Value
constValue (Full.ConstInt i) = Int i
constValue (Full.ConstFloat f) = Float f
constValue (Full.ConstString x) = String x
constValue (Full.ConstBoolean b) = Boolean b
constValue Full.ConstNull = Null
constValue (Full.ConstEnum e) = Enum e
constValue (Full.ConstList l) = List $ constValue <$> l
constValue (Full.ConstObject o) =
Object $ HashMap.fromList $ constObjectField <$> o
where
constObjectField (Full.ObjectField key value') = (key, constValue value')
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-- | Rewrites the original syntax tree into an intermediate representation used
-- for query execution.
document :: VariableValue a
=> forall m
. Schema m
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-> Maybe Full.Name
-> HashMap Full.Name a
-> Full.Document
-> Either QueryError (Document m)
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document schema operationName subs ast = do
let referencedTypes = collectReferencedTypes schema
(operations, fragmentTable) <- defragment ast
chosenOperation <- getOperation operationName operations
coercedValues <- coerceVariableValues referencedTypes chosenOperation subs
let replacement = Replacement
{ fragments = HashMap.empty
, fragmentDefinitions = fragmentTable
, variableValues = coercedValues
, types = referencedTypes
}
case chosenOperation of
OperationDefinition Full.Query _ _ _ _ ->
pure $ Document referencedTypes (query schema)
$ operation chosenOperation replacement
OperationDefinition Full.Mutation _ _ _ _
| Just mutationType <- mutation schema ->
pure $ Document referencedTypes mutationType
$ operation chosenOperation replacement
_ -> Left UnsupportedRootOperation
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defragment
:: Full.Document
-> Either QueryError (NonEmpty OperationDefinition, FragmentDefinitions)
defragment ast =
let (operations, fragmentTable) = foldr defragment' ([], HashMap.empty) ast
nonEmptyOperations = NonEmpty.nonEmpty operations
emptyDocument = Left EmptyDocument
in (, fragmentTable) <$> maybe emptyDocument Right nonEmptyOperations
where
defragment' definition (operations, fragments')
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| (Full.ExecutableDefinition executable) <- definition
, (Full.DefinitionOperation operation') <- executable =
(transform operation' : operations, fragments')
| (Full.ExecutableDefinition executable) <- definition
, (Full.DefinitionFragment fragment) <- executable
, (Full.FragmentDefinition name _ _ _) <- fragment =
(operations, HashMap.insert name fragment fragments')
defragment' _ acc = acc
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transform = \case
Full.OperationDefinition type' name variables directives' selections ->
OperationDefinition type' name variables directives' selections
Full.SelectionSet selectionSet ->
OperationDefinition Full.Query Nothing mempty mempty selectionSet
-- * Operation
operation :: OperationDefinition -> Replacement m -> Operation m
operation operationDefinition replacement
= runIdentity
$ evalStateT (collectFragments >> transform operationDefinition) replacement
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where
transform (OperationDefinition Full.Query name _ _ sels) =
Query name <$> appendSelection sels
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transform (OperationDefinition Full.Mutation name _ _ sels) =
Mutation name <$> appendSelection sels
-- * Selection
selection
:: Full.Selection
-> State (Replacement m) (Either (Seq (Selection m)) (Selection m))
selection (Full.Field alias name arguments' directives' selections) =
maybe (Left mempty) (Right . SelectionField) <$> do
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fieldArguments <- arguments arguments'
fieldSelections <- appendSelection selections
fieldDirectives <- Directive.selection <$> directives directives'
let field' = Field alias name fieldArguments fieldSelections
pure $ field' <$ fieldDirectives
selection (Full.FragmentSpread name directives') =
maybe (Left mempty) (Right . SelectionFragment) <$> do
spreadDirectives <- Directive.selection <$> directives directives'
fragments' <- gets fragments
fragmentDefinitions' <- gets fragmentDefinitions
case HashMap.lookup name fragments' of
Just definition -> lift $ pure $ definition <$ spreadDirectives
Nothing
| Just definition <- HashMap.lookup name fragmentDefinitions' -> do
fragDef <- fragmentDefinition definition
case fragDef of
Just fragment -> lift $ pure $ fragment <$ spreadDirectives
_ -> lift $ pure Nothing
| otherwise -> lift $ pure Nothing
selection (Full.InlineFragment type' directives' selections) = do
fragmentDirectives <- Directive.selection <$> directives directives'
case fragmentDirectives of
Nothing -> pure $ Left mempty
_ -> do
fragmentSelectionSet <- appendSelection selections
case type' of
Nothing -> pure $ Left fragmentSelectionSet
Just typeName -> do
typeCondition' <- lookupTypeCondition typeName
case typeCondition' of
Just typeCondition -> pure $
selectionFragment typeCondition fragmentSelectionSet
Nothing -> pure $ Left mempty
where
selectionFragment typeName = Right
. SelectionFragment
. Fragment typeName
appendSelection :: Traversable t
=> t Full.Selection
-> State (Replacement m) (Seq (Selection m))
appendSelection = foldM go mempty
where
go acc sel = append acc <$> selection sel
append acc (Left list) = list >< acc
append acc (Right one) = one <| acc
directives :: [Full.Directive] -> State (Replacement m) [Core.Directive]
directives = traverse directive
where
directive (Full.Directive directiveName directiveArguments) =
Core.Directive directiveName <$> arguments directiveArguments
-- * Fragment replacement
-- | Extract fragment definitions into a single 'HashMap'.
collectFragments :: State (Replacement m) ()
collectFragments = do
fragDefs <- gets fragmentDefinitions
let nextValue = head $ HashMap.elems fragDefs
unless (HashMap.null fragDefs) $ do
_ <- fragmentDefinition nextValue
collectFragments
lookupTypeCondition :: Full.Name -> State (Replacement m) (Maybe (CompositeType m))
lookupTypeCondition type' = do
types' <- gets types
case HashMap.lookup type' types' of
Just (ObjectType objectType) ->
lift $ pure $ Just $ CompositeObjectType objectType
Just (UnionType unionType) ->
lift $ pure $ Just $ CompositeUnionType unionType
Just (InterfaceType interfaceType) ->
lift $ pure $ Just $ CompositeInterfaceType interfaceType
_ -> lift $ pure Nothing
fragmentDefinition
:: Full.FragmentDefinition
-> State (Replacement m) (Maybe (Fragment m))
fragmentDefinition (Full.FragmentDefinition name type' _ selections) = do
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modify deleteFragmentDefinition
fragmentSelection <- appendSelection selections
compositeType <- lookupTypeCondition type'
case compositeType of
Just compositeType' -> do
let newValue = Fragment compositeType' fragmentSelection
modify $ insertFragment newValue
lift $ pure $ Just newValue
_ -> lift $ pure Nothing
where
deleteFragmentDefinition replacement@Replacement{..} =
let newDefinitions = HashMap.delete name fragmentDefinitions
in replacement{ fragmentDefinitions = newDefinitions }
insertFragment newValue replacement@Replacement{..} =
let newFragments = HashMap.insert name newValue fragments
in replacement{ fragments = newFragments }
arguments :: [Full.Argument] -> State (Replacement m) Core.Arguments
arguments = fmap Core.Arguments . foldM go HashMap.empty
where
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go arguments' (Full.Argument name value') = do
substitutedValue <- value value'
return $ HashMap.insert name substitutedValue arguments'
value :: Full.Value -> State (Replacement m) Value
value (Full.Variable name) =
gets $ fromMaybe Null . HashMap.lookup name . variableValues
value (Full.Int i) = pure $ Int i
value (Full.Float f) = pure $ Float f
value (Full.String x) = pure $ String x
value (Full.Boolean b) = pure $ Boolean b
value Full.Null = pure Null
value (Full.Enum e) = pure $ Enum e
value (Full.List l) = List <$> traverse value l
value (Full.Object o) =
Object . HashMap.fromList <$> traverse objectField o
objectField
:: Full.ObjectField Full.Value
-> State (Replacement m) (Full.Name, Value)
objectField (Full.ObjectField name value') = (name,) <$> value value'