Something is wrong with LBS.ByteString literals

[phadej]

See #392 for discovery.

By reducing test case to, which can be built with master:

{-# LANGUAGE CPP #-}
{-# LANGUAGE OverloadedStrings #-}
module Main (main) where

import           Test.Tasty (defaultMain, testGroup)
import           Test.Tasty.HUnit (testCase, (@=?))
import qualified Data.ByteString as BS
import qualified Data.ByteString.Lazy as LBS

main :: IO ()
main = defaultMain $ testGroup "bytestring-th"
  [ testGroup "lazy"
    [ testCase "binary" $ do
        let bs :: LBS.ByteString
            bs = "\0\1"


        bs @=? LBS.pack [0,1]

    ]
  ]

The Core with GHC-9.0.1 has terms:

-- RHS size: {terms: 1, types: 0, coercions: 0, joins: 0/0}
lvl1_r5QU :: ghc-prim-0.7.0:GHC.Prim.Addr#
[GblId, Unf=OtherCon []]
lvl1_r5QU = "\\128\SOH"#

-- RHS size: {terms: 2, types: 0, coercions: 0, joins: 0/0}
lvl2_r5QV :: [Char]
[GblId]
lvl2_r5QV = ghc-prim-0.7.0:GHC.CString.unpackCStringUtf8# lvl1_r5QU

ghci> unpackCStringUtf8# "\128\SOH"#
"\-4223"
ghci> (-4223) `mod` 256
129

which explain where from 129 comes from. But how those Core terms are generated, I don't know.

This happens with GHC-9.0 and GHC-9.2.0.20210422, but doesn't with GHC-8.x

---

cc @bgamari

[phadej]

Another data point. If I run script:

{- cabal:
build-depends: tasty, tasty-hunit, base, bytestring
-}
{-# LANGUAGE CPP #-}
{-# LANGUAGE OverloadedStrings #-}
module Main (main) where

import           Test.Tasty (defaultMain, testGroup)
import           Test.Tasty.HUnit (testCase, (@=?))
import qualified Data.ByteString as BS
import qualified Data.ByteString.Lazy as LBS

main :: IO ()
main = defaultMain $ testGroup "bytestring-th"
  [ testGroup "lazy"
    [ testCase "binary" $ do
        let bs :: LBS.ByteString
            bs = "\0\1"

        bs @=? LBS.pack [0,1]

    ]
  ]

with cabal run test-case.hs -w ghc-9.0.1 then it is fine, but

% cabal run test-case.hs -w ghc-9.2.0.20210422
Warning: Unknown/unsupported 'ghc' version detected (Cabal 3.4.0.0 supports
'ghc' version < 9.1): /opt/ghc/bin/ghc-9.2.0.20210422 is version
9.2.0.20210422
Resolving dependencies...
...

[1 of 1] Compiling Main             ( Main.hs, /tmp/cabal-repl.-128098/dist-newstyle/build/x86_64-linux/ghc-9.2.0.20210422/fake-package-0/x/script/build/script/script-tmp/Main.o )
Linking /tmp/cabal-repl.-128098/dist-newstyle/build/x86_64-linux/ghc-9.2.0.20210422/fake-package-0/x/script/build/script/script ...
bytestring-th
  lazy
    binary: FAIL
      Main.hs:20:
      expected: "\NUL\129"
       but got: "\NUL\SOH"

fails. So it looks that some recent change in bytestring triggers the issue.

[phadej]

This issue was GHC one, and now it's fixed.