Remove use of managed for starting the scenario service (#1508)

Ironically `managed` didn't turn out to make our code more manageable
and we ended up mostly using it in very isolated places only to then
immediately convert it back to bracket-style functions using `with`.

This PR also removes the use of `managed` from the GcpLogger which was
the only other place where we are using it and it finally kills the
rather silly logic that starting up the scenario service was tied to
having an event logger.

src/Development/IDE/State/Service.hs

@@ -24,7 +24,6 @@ import           Control.Monad.Except
 import Development.IDE.Types.Options (IdeOptions(..))
 import           Development.IDE.State.FileStore
 import qualified Development.IDE.Logger as Logger
-import Data.Maybe
 import           Data.Set                                 (Set)
 import qualified Data.Set                                 as Set
 import           Development.IDE.Functions.GHCError
@@ -70,14 +69,14 @@ unsafeClearDiagnostics = unsafeClearAllDiagnostics
 
 -- | Initialise the Compiler Service.
 initialise :: Rules ()
-           -> Maybe (Event -> IO ())
+           -> (Event -> IO ())
            -> Logger.Handle
            -> IdeOptions
            -> VFSHandle
            -> IO IdeState
 initialise mainRule toDiags logger options vfs =
     shakeOpen
-        (fromMaybe (const $ pure ()) toDiags)
+        toDiags
         logger
         (setProfiling options $
         shakeOptions { shakeThreads = optThreads options

src/Development/IDE/Types/LSP.hs

@@ -52,7 +52,4 @@ data Event
     | EventFileValidation Int Int
       -- ^ @EventFileValidation finishedValidations totalValidations @
       -- How many validations have we finished of how many total.
-    | EventFatalError !T.Text
-      -- ^ @EventFatalError reason@: A fatal error occurred in the compiler and
-      -- the compiler cannot continue.
       deriving Show

test/Demo.hs

@@ -42,7 +42,7 @@ main = do
     vfs <- makeVFSHandle
     ide <- initialise
         mainRule
-        (Just $ showEvent lock)
+        (showEvent lock)
         (makeOneHandle $ withLock lock . T.putStrLn)
         IdeOptions
             {optPreprocessor = (,) []