Support being built with ghc 8.0.1 (MonadFail)

Tested on an older ghc by enabling MonadFailDesugaring globally.

In TransferQueue, the lack of a MonadFail for STM exposed what would
normally be a bug in the pattern matching, although in this case an
earlier check that the queue was not empty avoided a pattern match
failure.
This commit is contained in:
Joey Hess 2019-01-05 11:54:06 -04:00
parent 6ec993252e
commit 2e0e557e75
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4 changed files with 16 additions and 10 deletions

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@ -191,16 +191,17 @@ getNextTransfer acceptable = do
sz <- readTVar (queuesize q)
if sz < 1
then retry -- blocks until queuesize changes
else do
(r@(t,info):rest) <- readTList (queuelist q)
void $ modifyTVar' (queuesize q) pred
setTList (queuelist q) rest
if acceptable info
then do
adjustTransfersSTM dstatus $
M.insert t info
return $ Just r
else return Nothing
else readTList (queuelist q) >>= \case
[] -> retry -- blocks until something is queued
(r@(t,info):rest) -> do
void $ modifyTVar' (queuesize q) pred
setTList (queuelist q) rest
if acceptable info
then do
adjustTransfersSTM dstatus $
M.insert t info
return $ Just r
else return Nothing
{- Moves transfers matching a condition from the queue, to the
- currentTransfers map. -}