*Really*, really fix RTS crash due to bad coercion.

Summary:
My previous attempt to fix the new coercion bug introduced by my fix actually
just reverted back to the *old* bug. This time it should properly handle all
three size scenarios.

Signed-off-by: Merijn Verstraaten <merijn@inconsistent.nl>

Test Plan: validate

Reviewers: dfeuer, austin, hvr

Reviewed By: austin, hvr

Subscribers: thomie, carter, simonmar

Differential Revision: https://phabricator.haskell.org/D407

GHC Trac Issues: #8089

1 files changed, 32 insertions, 0 deletions

diff --git a/libraries/base/tests/T8089.hs b/libraries/base/tests/T8089.hs
new file mode 100644
index 0000000000..2b98f94198
--- /dev/null
+++ b/libraries/base/tests/T8089.hs
@@ -0,0 +1,32 @@
+import Control.Applicative
+import Control.Concurrent
+import Control.Exception
+import Control.Monad
+import System.Environment
+import System.Exit
+import System.Process
+import System.Timeout
+
+testLoop :: Int -> IO (Maybe a) -> IO (Maybe a)
+testLoop 0 _ = return Nothing
+testLoop i act = do
+    result <- act
+    case result of
+        Nothing -> threadDelay 100000 >> testLoop (i-1) act
+        Just x -> return (Just x)
+
+
+forkTestChild :: IO ()
+forkTestChild = do
+    (_, _, _, hnd) <- createProcess (proc "./T8089" ["test"])
+    result <- testLoop 50 $ getProcessExitCode hnd
+    case result of
+        Nothing -> terminateProcess hnd >> exitSuccess
+        Just exitCode -> exitWith exitCode
+
+main :: IO ()
+main = do
+    numArgs <- length <$> getArgs
+    if numArgs > 0
+       then threadDelay maxBound
+       else forkTestChild