From 00e2a8a3271783bcebaa8b4b167bcfdc0f247332 Mon Sep 17 00:00:00 2001
From: Simon Michael <simon@joyful.com>
Date: Wed, 7 Dec 2016 07:52:10 -0800
Subject: [PATCH] lib: note a problem with dbg*IO

---
 hledger-lib/Hledger/Utils/Debug.hs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/hledger-lib/Hledger/Utils/Debug.hs b/hledger-lib/Hledger/Utils/Debug.hs
index 3da3daf9f..6c65135b3 100644
--- a/hledger-lib/Hledger/Utils/Debug.hs
+++ b/hledger-lib/Hledger/Utils/Debug.hs
@@ -117,6 +117,9 @@ dbg9 = tracePrettyAt 9
 
 -- | Convenience aliases for tracePrettyAtIO.
 -- Like dbg, but convenient to insert in an IO monad.
+-- XXX These have a bug; they should use traceIO, not trace,
+-- otherwise GHC can occasionally over-optimise
+-- (cf lpaste a few days ago where it killed/blocked a child thread).
 dbg0IO :: (MonadIO m, Show a) => String -> a -> m ()
 dbg0IO = tracePrettyAtIO 0