426 lines
17 KiB
Haskell
426 lines
17 KiB
Haskell
{- This Source Code Form is subject to the terms of the Mozilla Public License,
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v. 2.0. If a copy of the MPL was not distributed with this file, You can
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obtain one at https://mozilla.org/MPL/2.0/. -}
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{-# LANGUAGE ExplicitForAll #-}
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{-# LANGUAGE LambdaCase #-}
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{-# LANGUAGE OverloadedStrings #-}
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{-# LANGUAGE RecordWildCards #-}
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{-# LANGUAGE TupleSections #-}
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-- | After the document is parsed, before getting executed, the AST is
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-- transformed into a similar, simpler AST. Performed transformations include:
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--
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-- * Replacing variables with their values.
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-- * Inlining fragments. Some fragments can be completely eliminated and
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-- replaced by the selection set they represent. Invalid (recursive and
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-- non-existing) fragments are skipped. The most fragments are inlined, so the
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-- executor doesn't have to perform additional lookups later.
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-- * Evaluating directives (@\@include@ and @\@skip@).
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--
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-- This module is also responsible for smaller rewrites that touch only parts of
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-- the original AST.
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module Language.GraphQL.Execute.Transform
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( Document(..)
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, Field(..)
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, Fragment(..)
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, Input(..)
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, Operation(..)
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, QueryError(..)
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, Selection(..)
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, document
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) where
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import Control.Monad (foldM, unless)
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import Control.Monad.Trans.Class (lift)
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import Control.Monad.Trans.State (State, evalStateT, gets, modify)
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import Data.Foldable (find)
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import Data.Functor.Identity (Identity(..))
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import Data.HashMap.Strict (HashMap)
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import qualified Data.HashMap.Strict as HashMap
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import Data.Int (Int32)
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import Data.Maybe (fromMaybe)
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import Data.List.NonEmpty (NonEmpty(..))
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import qualified Data.List.NonEmpty as NonEmpty
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import Data.Sequence (Seq, (<|), (><))
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import Data.Text (Text)
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import qualified Data.Text as Text
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import qualified Language.GraphQL.AST as Full
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import Language.GraphQL.AST (Name)
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import qualified Language.GraphQL.Execute.Coerce as Coerce
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import qualified Language.GraphQL.Type.Definition as Definition
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import qualified Language.GraphQL.Type as Type
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import qualified Language.GraphQL.Type.Internal as Type
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import qualified Language.GraphQL.Type.Out as Out
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import qualified Language.GraphQL.Type.Schema as Schema
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-- | Associates a fragment name with a list of 'Field's.
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data Replacement m = Replacement
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{ fragments :: HashMap Full.Name (Fragment m)
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, fragmentDefinitions :: FragmentDefinitions
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, variableValues :: Type.Subs
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, types :: HashMap Full.Name (Schema.Type m)
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}
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type FragmentDefinitions = HashMap Full.Name Full.FragmentDefinition
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-- | Represents fragments and inline fragments.
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data Fragment m
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= Fragment (Type.CompositeType m) (Seq (Selection m))
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-- | Single selection element.
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data Selection m
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= SelectionFragment (Fragment m)
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| SelectionField (Field m)
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-- | GraphQL has 3 operation types: queries, mutations and subscribtions.
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data Operation m
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= Query (Maybe Text) (Seq (Selection m)) Full.Location
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| Mutation (Maybe Text) (Seq (Selection m)) Full.Location
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| Subscription (Maybe Text) (Seq (Selection m)) Full.Location
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-- | Single GraphQL field.
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data Field m = Field
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(Maybe Full.Name)
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Full.Name
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(HashMap Full.Name (Full.Node Input))
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(Seq (Selection m))
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Full.Location
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-- | Contains the operation to be executed along with its root type.
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data Document m = Document
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(HashMap Full.Name (Schema.Type m)) (Out.ObjectType m) (Operation m)
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data OperationDefinition = OperationDefinition
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Full.OperationType
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(Maybe Full.Name)
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[Full.VariableDefinition]
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[Full.Directive]
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Full.SelectionSet
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Full.Location
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-- | Query error types.
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data QueryError
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= OperationNotFound Text
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| OperationNameRequired
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| CoercionError
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| EmptyDocument
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| UnsupportedRootOperation
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instance Show QueryError where
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show (OperationNotFound operationName) = unwords
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["Operation", Text.unpack operationName, "couldn't be found in the document."]
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show OperationNameRequired = "Missing operation name."
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show CoercionError = "Coercion error."
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show EmptyDocument =
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"The document doesn't contain any executable operations."
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show UnsupportedRootOperation =
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"Root operation type couldn't be found in the schema."
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data Input
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= Int Int32
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| Float Double
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| String Text
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| Boolean Bool
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| Null
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| Enum Name
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| List [Type.Value]
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| Object (HashMap Name Input)
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| Variable Type.Value
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deriving (Eq, Show)
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getOperation
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:: Maybe Full.Name
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-> NonEmpty OperationDefinition
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-> Either QueryError OperationDefinition
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getOperation Nothing (operation' :| []) = pure operation'
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getOperation Nothing _ = Left OperationNameRequired
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getOperation (Just operationName) operations
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| Just operation' <- find matchingName operations = pure operation'
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| otherwise = Left $ OperationNotFound operationName
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where
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matchingName (OperationDefinition _ name _ _ _ _) =
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name == Just operationName
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coerceVariableValues :: Coerce.VariableValue a
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=> forall m
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. HashMap Full.Name (Schema.Type m)
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-> OperationDefinition
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-> HashMap.HashMap Full.Name a
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-> Either QueryError Type.Subs
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coerceVariableValues types operationDefinition variableValues =
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let OperationDefinition _ _ variableDefinitions _ _ _ = operationDefinition
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in maybe (Left CoercionError) Right
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$ foldr forEach (Just HashMap.empty) variableDefinitions
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where
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forEach variableDefinition coercedValues = do
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let Full.VariableDefinition variableName variableTypeName defaultValue _ =
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variableDefinition
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let defaultValue' = constValue . Full.node <$> defaultValue
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variableType <- Type.lookupInputType variableTypeName types
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Coerce.matchFieldValues
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coerceVariableValue'
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variableValues
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variableName
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variableType
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defaultValue'
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coercedValues
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coerceVariableValue' variableType value'
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= Coerce.coerceVariableValue variableType value'
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>>= Coerce.coerceInputLiteral variableType
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constValue :: Full.ConstValue -> Type.Value
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constValue (Full.ConstInt i) = Type.Int i
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constValue (Full.ConstFloat f) = Type.Float f
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constValue (Full.ConstString x) = Type.String x
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constValue (Full.ConstBoolean b) = Type.Boolean b
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constValue Full.ConstNull = Type.Null
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constValue (Full.ConstEnum e) = Type.Enum e
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constValue (Full.ConstList list) = Type.List $ constValue . Full.node <$> list
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constValue (Full.ConstObject o) =
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Type.Object $ HashMap.fromList $ constObjectField <$> o
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where
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constObjectField Full.ObjectField{value = value', ..} =
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(name, constValue $ Full.node value')
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-- | Rewrites the original syntax tree into an intermediate representation used
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-- for query execution.
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document :: Coerce.VariableValue a
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=> forall m
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. Type.Schema m
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-> Maybe Full.Name
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-> HashMap Full.Name a
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-> Full.Document
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-> Either QueryError (Document m)
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document schema operationName subs ast = do
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let referencedTypes = Schema.types schema
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(operations, fragmentTable) <- defragment ast
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chosenOperation <- getOperation operationName operations
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coercedValues <- coerceVariableValues referencedTypes chosenOperation subs
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let replacement = Replacement
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{ fragments = HashMap.empty
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, fragmentDefinitions = fragmentTable
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, variableValues = coercedValues
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, types = referencedTypes
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}
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case chosenOperation of
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OperationDefinition Full.Query _ _ _ _ _ ->
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pure $ Document referencedTypes (Schema.query schema)
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$ operation chosenOperation replacement
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OperationDefinition Full.Mutation _ _ _ _ _
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| Just mutationType <- Schema.mutation schema ->
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pure $ Document referencedTypes mutationType
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$ operation chosenOperation replacement
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OperationDefinition Full.Subscription _ _ _ _ _
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| Just subscriptionType <- Schema.subscription schema ->
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pure $ Document referencedTypes subscriptionType
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$ operation chosenOperation replacement
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_ -> Left UnsupportedRootOperation
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defragment
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:: Full.Document
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-> Either QueryError (NonEmpty OperationDefinition, FragmentDefinitions)
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defragment ast =
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let (operations, fragmentTable) = foldr defragment' ([], HashMap.empty) ast
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nonEmptyOperations = NonEmpty.nonEmpty operations
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emptyDocument = Left EmptyDocument
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in (, fragmentTable) <$> maybe emptyDocument Right nonEmptyOperations
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where
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defragment' definition (operations, fragments')
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| (Full.ExecutableDefinition executable) <- definition
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, (Full.DefinitionOperation operation') <- executable =
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(transform operation' : operations, fragments')
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| (Full.ExecutableDefinition executable) <- definition
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, (Full.DefinitionFragment fragment) <- executable
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, (Full.FragmentDefinition name _ _ _ _) <- fragment =
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(operations, HashMap.insert name fragment fragments')
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defragment' _ acc = acc
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transform = \case
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Full.OperationDefinition type' name variables directives' selections location ->
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OperationDefinition type' name variables directives' selections location
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Full.SelectionSet selectionSet location ->
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OperationDefinition Full.Query Nothing mempty mempty selectionSet location
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-- * Operation
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operation :: OperationDefinition -> Replacement m -> Operation m
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operation operationDefinition replacement
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= runIdentity
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$ evalStateT (collectFragments >> transform operationDefinition) replacement
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where
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transform (OperationDefinition Full.Query name _ _ sels location) =
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flip (Query name) location <$> appendSelection sels
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transform (OperationDefinition Full.Mutation name _ _ sels location) =
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flip (Mutation name) location <$> appendSelection sels
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transform (OperationDefinition Full.Subscription name _ _ sels location) =
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flip (Subscription name) location <$> appendSelection sels
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-- * Selection
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selection
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:: Full.Selection
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-> State (Replacement m) (Either (Seq (Selection m)) (Selection m))
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selection (Full.FieldSelection fieldSelection) =
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maybe (Left mempty) (Right . SelectionField) <$> field fieldSelection
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selection (Full.FragmentSpreadSelection fragmentSelection)
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= maybe (Left mempty) (Right . SelectionFragment)
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<$> fragmentSpread fragmentSelection
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selection (Full.InlineFragmentSelection fragmentSelection) =
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inlineFragment fragmentSelection
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field :: Full.Field -> State (Replacement m) (Maybe (Field m))
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field (Full.Field alias name arguments' directives' selections location) = do
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fieldArguments <- foldM go HashMap.empty arguments'
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fieldSelections <- appendSelection selections
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fieldDirectives <- Definition.selection <$> directives directives'
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let field' = Field alias name fieldArguments fieldSelections location
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pure $ field' <$ fieldDirectives
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where
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go arguments (Full.Argument name' (Full.Node value' _) location') = do
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objectFieldValue <- input value'
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case objectFieldValue of
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Just fieldValue ->
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let argumentNode = Full.Node fieldValue location'
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in pure $ HashMap.insert name' argumentNode arguments
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Nothing -> pure arguments
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fragmentSpread
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:: Full.FragmentSpread
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-> State (Replacement m) (Maybe (Fragment m))
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fragmentSpread (Full.FragmentSpread name directives' _) = do
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spreadDirectives <- Definition.selection <$> directives directives'
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fragments' <- gets fragments
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fragmentDefinitions' <- gets fragmentDefinitions
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case HashMap.lookup name fragments' of
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Just definition -> lift $ pure $ definition <$ spreadDirectives
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Nothing
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| Just definition <- HashMap.lookup name fragmentDefinitions' -> do
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fragDef <- fragmentDefinition definition
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case fragDef of
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Just fragment -> lift $ pure $ fragment <$ spreadDirectives
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_ -> lift $ pure Nothing
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| otherwise -> lift $ pure Nothing
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inlineFragment
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:: Full.InlineFragment
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-> State (Replacement m) (Either (Seq (Selection m)) (Selection m))
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inlineFragment (Full.InlineFragment type' directives' selections _) = do
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fragmentDirectives <- Definition.selection <$> directives directives'
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case fragmentDirectives of
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Nothing -> pure $ Left mempty
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_ -> do
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fragmentSelectionSet <- appendSelection selections
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case type' of
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Nothing -> pure $ Left fragmentSelectionSet
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Just typeName -> do
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types' <- gets types
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case Type.lookupTypeCondition typeName types' of
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Just typeCondition -> pure $
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selectionFragment typeCondition fragmentSelectionSet
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Nothing -> pure $ Left mempty
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where
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selectionFragment typeName = Right
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. SelectionFragment
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. Fragment typeName
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appendSelection :: Traversable t
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=> t Full.Selection
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-> State (Replacement m) (Seq (Selection m))
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appendSelection = foldM go mempty
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where
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go acc sel = append acc <$> selection sel
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append acc (Left list) = list >< acc
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append acc (Right one) = one <| acc
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directives :: [Full.Directive] -> State (Replacement m) [Definition.Directive]
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directives = traverse directive
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where
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directive (Full.Directive directiveName directiveArguments _)
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= Definition.Directive directiveName . Type.Arguments
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<$> foldM go HashMap.empty directiveArguments
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go arguments (Full.Argument name (Full.Node value' _) _) = do
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substitutedValue <- value value'
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return $ HashMap.insert name substitutedValue arguments
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-- * Fragment replacement
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-- | Extract fragment definitions into a single 'HashMap'.
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collectFragments :: State (Replacement m) ()
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collectFragments = do
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fragDefs <- gets fragmentDefinitions
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let nextValue = head $ HashMap.elems fragDefs
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unless (HashMap.null fragDefs) $ do
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_ <- fragmentDefinition nextValue
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collectFragments
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fragmentDefinition
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:: Full.FragmentDefinition
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-> State (Replacement m) (Maybe (Fragment m))
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fragmentDefinition (Full.FragmentDefinition name type' _ selections _) = do
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modify deleteFragmentDefinition
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fragmentSelection <- appendSelection selections
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types' <- gets types
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case Type.lookupTypeCondition type' types' of
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Just compositeType -> do
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let newValue = Fragment compositeType fragmentSelection
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modify $ insertFragment newValue
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lift $ pure $ Just newValue
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_ -> lift $ pure Nothing
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where
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deleteFragmentDefinition replacement@Replacement{..} =
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let newDefinitions = HashMap.delete name fragmentDefinitions
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in replacement{ fragmentDefinitions = newDefinitions }
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insertFragment newValue replacement@Replacement{..} =
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let newFragments = HashMap.insert name newValue fragments
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in replacement{ fragments = newFragments }
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value :: forall m. Full.Value -> State (Replacement m) Type.Value
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value (Full.Variable name) =
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gets (fromMaybe Type.Null . HashMap.lookup name . variableValues)
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value (Full.Int int) = pure $ Type.Int int
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value (Full.Float float) = pure $ Type.Float float
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value (Full.String string) = pure $ Type.String string
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value (Full.Boolean boolean) = pure $ Type.Boolean boolean
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value Full.Null = pure Type.Null
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value (Full.Enum enum) = pure $ Type.Enum enum
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value (Full.List list) = Type.List <$> traverse (value . Full.node) list
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value (Full.Object object) =
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Type.Object . HashMap.fromList <$> traverse objectField object
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where
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objectField Full.ObjectField{value = value', ..} =
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(name,) <$> value (Full.node value')
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input :: forall m. Full.Value -> State (Replacement m) (Maybe Input)
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input (Full.Variable name) =
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gets (fmap Variable . HashMap.lookup name . variableValues)
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input (Full.Int int) = pure $ pure $ Int int
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input (Full.Float float) = pure $ pure $ Float float
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input (Full.String string) = pure $ pure $ String string
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input (Full.Boolean boolean) = pure $ pure $ Boolean boolean
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input Full.Null = pure $ pure Null
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input (Full.Enum enum) = pure $ pure $ Enum enum
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input (Full.List list) = pure . List <$> traverse (value . Full.node) list
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input (Full.Object object) = do
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objectFields <- foldM objectField HashMap.empty object
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pure $ pure $ Object objectFields
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where
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objectField resultMap Full.ObjectField{value = value', ..} =
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inputField resultMap name $ Full.node value'
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inputField :: forall m
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. HashMap Full.Name Input
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-> Full.Name
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-> Full.Value
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-> State (Replacement m) (HashMap Full.Name Input)
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inputField resultMap name value' = do
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objectFieldValue <- input value'
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case objectFieldValue of
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Just fieldValue -> pure $ HashMap.insert name fieldValue resultMap
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Nothing -> pure resultMap
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