Catch exceptions in message formatting

[larsrh]

Same as UnkindPartition/tasty#25. The console reporter deals with it, but not tasty-html.

[larsrh]

Relevant code in tasty: https://github.com/feuerbach/tasty/blob/8eae8007ad60c8ce0041f0976139ed489d367c9c/core/Test/Tasty/Ingredients/ConsoleReporter.hs#L465-L479

-- | Printing exceptions or other messages is tricky — in the process we
-- can get new exceptions!
-- 
-- See e.g. https://github.com/feuerbach/tasty/issues/25
formatMessage :: String -> IO String
formatMessage msg = go 3 msg
where
-- to avoid infinite recursion, we introduce the recursion limit
go :: Int -> String -> IO String
go 0 _ = return "exceptions keep throwing other exceptions!"
go recLimit msg = do
mbStr <- try $ evaluate $ force msg
case mbStr of
Right str -> return str
Left e' -> printf "message threw an exception: %s" <$> go (recLimit-1) (show (e' :: SomeException))

[noschinl]

The commit referenced fixes this issue by copying the formatMessage code from Tasty. One could argue that it would if Tasty exported this function. I'm willing to provide pull requests to implement that.

[UnkindPartition]

Sure, I'll export formatMessage later today.

[UnkindPartition]

Done, Test.Tasty.Runners.formatMessage is exported by tasty-0.10.1.