[Haskell-cafe] Debugging a test suite freeze

[Li-yao Xia]

GHC 9.4.3 with -O2 is miscompiling the derived Show and Eq instances for 
SeqT in logict-sequence.

     main :: IO ()
     main = print (pure 0 :: Seq Int)
     -- -O0, -O1: prints the Seq
     -- -O2: <<loop>>

On top of that, both hedgehog and hspec fail to catch `<<loop>>`.

     main :: IO ()
     main = defaultMain
       [ check $ property $ do
           let x = x :: Int  -- obvious loop compiles to a thrown 
exception <<loop>>
           if x == x then pure () else pure ()  ]
     -- "thread blocked indefinitely in an STM transaction"
     -- meaning some thread is not getting cleaned up properly

     main :: IO ()
     main = hspec $ do
       describe "work" $ do
         it "works" $ do
           let x = x :: Int  -- obvious loop compiles to a thrown 
exception <<loop>>
           if x == x then pure () else pure () :: IO ()
     --- hangs

Cheers,
Li-yao


On 2022-11-30 10:33 PM, David Feuer wrote:

The logict-sequence test suite consistently freezes up on the last
test when compiled with GHC 9.4.3. logict-sequence and its test suite
don't do anything special with that GHC/base version as far as I can
see, or anything particularly strange in general, so I'm pretty
confident the problem lies elsewhere. My best guesses are hedgehog,
tasty, and tasty-hedgehog. Has anyone else run into weird issues with
any/all of these on GHC 9.4.3?

David
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