89 lines
2.9 KiB
Haskell
89 lines
2.9 KiB
Haskell
{-# LANGUAGE OverloadedStrings #-}
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{-# LANGUAGE RecordWildCards #-}
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-- | Error handling.
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module Language.GraphQL.Error
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( parseError
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, CollectErrsT
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, addErr
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, addErrMsg
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, runCollectErrs
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, runAppendErrs
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, singleError
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) where
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import qualified Data.Aeson as Aeson
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import Data.Text (Text)
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import Data.Void (Void)
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import Control.Monad.Trans.Class (lift)
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import Control.Monad.Trans.State ( StateT
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, modify
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, runStateT
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)
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import Text.Megaparsec
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( ParseErrorBundle(..)
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, PosState(..)
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, SourcePos(..)
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, errorOffset
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, parseErrorTextPretty
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, reachOffset
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, unPos
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)
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-- | Wraps a parse error into a list of errors.
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parseError :: Applicative f => ParseErrorBundle Text Void -> f Aeson.Value
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parseError ParseErrorBundle{..} =
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pure $ Aeson.object [("errors", Aeson.toJSON $ fst $ foldl go ([], bundlePosState) bundleErrors)]
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where
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errorObject s SourcePos{..} = Aeson.object
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[ ("message", Aeson.toJSON $ init $ parseErrorTextPretty s)
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, ("line", Aeson.toJSON $ unPos sourceLine)
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, ("column", Aeson.toJSON $ unPos sourceColumn)
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]
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go (result, state) x =
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let (_, newState) = reachOffset (errorOffset x) state
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sourcePosition = pstateSourcePos newState
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in (errorObject x sourcePosition : result, newState)
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-- | A wrapper to pass error messages around.
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type CollectErrsT m = StateT [Aeson.Value] m
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-- | Adds an error to the list of errors.
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addErr :: Monad m => Aeson.Value -> CollectErrsT m ()
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addErr v = modify (v :)
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makeErrorMessage :: Text -> Aeson.Value
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makeErrorMessage s = Aeson.object [("message", Aeson.toJSON s)]
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-- | Constructs a response object containing only the error with the given
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-- message.
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singleError :: Text -> Aeson.Value
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singleError message = Aeson.object
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[ ("errors", Aeson.toJSON [makeErrorMessage message])
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]
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-- | Convenience function for just wrapping an error message.
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addErrMsg :: Monad m => Text -> CollectErrsT m ()
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addErrMsg = addErr . makeErrorMessage
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-- | Appends the given list of errors to the current list of errors.
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appendErrs :: Monad m => [Aeson.Value] -> CollectErrsT m ()
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appendErrs errs = modify (errs ++)
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-- | Runs the given query computation, but collects the errors into an error
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-- list, which is then sent back with the data.
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runCollectErrs :: Monad m => CollectErrsT m Aeson.Value -> m Aeson.Value
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runCollectErrs res = do
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(dat, errs) <- runStateT res []
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if null errs
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then return $ Aeson.object [("data", dat)]
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else return $ Aeson.object [("data", dat), ("errors", Aeson.toJSON $ reverse errs)]
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-- | Runs the given computation, collecting the errors and appending them
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-- to the previous list of errors.
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runAppendErrs :: Monad m => CollectErrsT m a -> CollectErrsT m a
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runAppendErrs f = do
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(v, errs) <- lift $ runStateT f []
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appendErrs errs
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return v
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