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{-# LANGUAGE ScopedTypeVariables #-}
module Propellor.Exception where
import Propellor.Types
import Propellor.Message
import Utility.Exception
import Control.Exception (AsyncException)
import Control.Monad.Catch
import Control.Monad.IO.Class (MonadIO)
import Data.Typeable
-- | Normally when an exception is encountered while propellor is
-- ensuring a property, the property fails, but propellor robustly
-- continues on to the next property.
--
-- This is the only exception that will stop the entire propellor run,
-- preventing any subsequent properties of the Host from being ensured.
-- (When propellor is running in a container in a Host, this exception only
-- stops the propellor run in the container; the outer run in the Host
-- continues.)
--
-- You should only throw this exception when things are so badly messed up
-- that it's best for propellor to not try to do anything else.
data StopPropellorException = StopPropellorException String
deriving (Show, Typeable)
instance Exception StopPropellorException
-- | Catches all exceptions (except for `StopPropellorException` and
-- `AsyncException`) and returns FailedChange.
catchPropellor :: (MonadIO m, MonadCatch m) => m Result -> m Result
catchPropellor a = either err return =<< tryPropellor a
where
err e = warningMessage (show e) >> return FailedChange
catchPropellor' :: MonadCatch m => m a -> (SomeException -> m a) -> m a
catchPropellor' a onerr = a `catches`
[ Handler (\ (e :: AsyncException) -> throwM e)
, Handler (\ (e :: StopPropellorException) -> throwM e)
, Handler (\ (e :: SomeException) -> onerr e)
]
-- | Catches all exceptions (except for `StopPropellorException` and
-- `AsyncException`).
tryPropellor :: MonadCatch m => m a -> m (Either SomeException a)
tryPropellor a = (Right <$> a) `catchPropellor'` (pure . Left)
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