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Document exception handling in Actions/Rules (#3407)
* Document exception handling in Actions/Rules I also took the liberty of removing the `MonadFail` instance for `Rules`, since failing in `Rules` seems much worse as it won't automatically be caught. There was only one use of that, which now has an appropriately threatening comment. * Tweak Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
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@ -307,13 +307,17 @@ type GetStalePersistent = NormalizedFilePath -> IdeAction (Maybe (Dynamic,Positi
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getShakeExtras :: Action ShakeExtras
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getShakeExtras = do
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-- Will fail the action with a pattern match failure, but be caught
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Just x <- getShakeExtra @ShakeExtras
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return x
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getShakeExtrasRules :: Rules ShakeExtras
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getShakeExtrasRules = do
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Just x <- getShakeExtraRules @ShakeExtras
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return x
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mExtras <- getShakeExtraRules @ShakeExtras
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case mExtras of
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Just x -> return x
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-- This will actually crash HLS
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Nothing -> liftIO $ fail "missing ShakeExtras"
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-- | Returns the client configuration, creating a build dependency.
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-- You should always use this function when accessing client configuration
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@ -54,8 +54,13 @@ unwrapDynamic x = fromMaybe (error msg) $ fromDynamic x
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type TheRules = Map.HashMap TypeRep Dynamic
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-- | A computation that defines all the rules that form part of the computation graph.
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--
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-- 'Rules' has access to 'IO' through 'MonadIO'. Use of 'IO' is at your own risk: if
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-- you write 'Rules' that throw exceptions, then you need to make sure to handle them
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-- yourself when you run the resulting 'Rules'.
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newtype Rules a = Rules (ReaderT SRules IO a)
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deriving newtype (Monad, Applicative, Functor, MonadIO, MonadFail)
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deriving newtype (Monad, Applicative, Functor, MonadIO)
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data SRules = SRules {
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rulesExtra :: !Dynamic,
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@ -67,6 +72,12 @@ data SRules = SRules {
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---------------------------------------------------------------------
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-- ACTIONS
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-- | An action representing something that can be run as part of a 'Rule'.
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--
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-- 'Action's can be pure functions but also have access to 'IO' via 'MonadIO' and 'MonadUnliftIO.
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-- It should be assumed that actions throw exceptions, these can be caught with
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-- 'Development.IDE.Graph.Internal.Action.actionCatch'. In particular, it is
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-- permissible to use the 'MonadFail' instance, which will lead to an 'IOException'.
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newtype Action a = Action {fromAction :: ReaderT SAction IO a}
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deriving newtype (Monad, Applicative, Functor, MonadIO, MonadFail, MonadThrow, MonadCatch, MonadMask, MonadUnliftIO)
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