Implement recordingTracerM to avoid affecting the scheduling of execu…

…tion

ouroboros-consensus-diffusion/test/consensus-test/Test/Consensus/Genesis/Setup.hs

@@ -35,7 +35,7 @@ import           Test.QuickCheck
 import           Test.Util.Orphans.IOLike ()
 import           Test.Util.QuickCheck (forAllGenRunShrinkCheck)
 import           Test.Util.TestBlock (TestBlock)
-import           Test.Util.Tracer (recordingTracerTVar)
+import           Test.Util.Tracer (recordingTracerM)
 import           Text.Printf (printf)
 
 
@@ -56,7 +56,7 @@ runGenesisTest ::
   RunGenesisTestResult
 runGenesisTest schedulerConfig genesisTest =
   runSimStrictShutdownOrThrow $ do
-    (recordingTracer, getTrace) <- recordingTracerTVar
+    (recordingTracer, getTrace) <- recordingTracerM
     let tracer = if scDebug schedulerConfig then debugTracer else recordingTracer
 
     traceLinesWith tracer $ prettyGenesisTest prettyPeersSchedule genesisTest

ouroboros-consensus/src/unstable-consensus-testlib/Test/Util/Tracer.hs

@@ -1,11 +1,14 @@
+{-# LANGUAGE ScopedTypeVariables #-}
 module Test.Util.Tracer (
     recordingTracerIORef
+  , recordingTracerM
   , recordingTracerTVar
   ) where
 
 import           Control.Tracer
 import           Data.IORef
 import           Ouroboros.Consensus.Util.IOLike
+import           System.IO.Unsafe (unsafePerformIO)
 
 -- | Create a 'Tracer' that stores all events in an 'IORef' that is atomically
 -- updated. The second return value lets you obtain the events recorded so far
@@ -24,3 +27,26 @@ recordingTracerTVar = uncheckedNewTVarM [] >>= \ref -> return
     ( Tracer $ \ev -> atomically $ modifyTVar ref (ev:)
     , atomically $ reverse <$> readTVar ref
     )
+
+-- | Like 'recordingTracerIORef', but lifts IO to an arbitrary applicative.
+-- This is useful to record events without changing the scheduling during a
+-- test.
+recordingTracerM :: forall m ev. Monad m => m (Tracer m ev, m [ev])
+recordingTracerM = do
+  (tr, get) <- liftIOtoM recordingTracerIORef
+  pure (natTracer liftIOtoM tr, liftIOtoM get)
+  where
+    liftIOtoM :: IO a -> m a
+    liftIOtoM m = do
+      -- The ficticious state is only used to force unsafePerformIO to run @m@
+      -- every time @liftIOtoM m@ is evaluated.
+      s <- getStateM
+      pure $! snd $ unsafePerformIO $ do
+        r <- m
+        pure (s, r)
+
+    -- We mark this function as NOINLINE to ensure the compiler cannot reason
+    -- that two calls of @getStateM@ might yield the same value.
+    {-# NOINLINE getStateM #-}
+    getStateM :: m Int
+    getStateM = pure 0