GHC does not pass -dstg-lint
When building ghc-8.4 branch with -dstg-lint enabled I got a GHC panic error (please see attachment for full log as it's really big). The error is reproducible on Windows and Debian Linux 64 bit operating systems.
"inplace/bin/ghc-stage1" -hisuf hi -osuf o -hcsuf hc -static -O -H64m -Wall -this-unit-id ghc-prim-0.5.2.0 -hide-all-packages -i -ilibraries/ghc-prim/. -ilibraries/ghc-prim/dist-install/build -Ilibraries/ghc-prim/dist-install/build -ilibraries/ghc-prim/dist-install/build/./autogen -Ilibraries/ghc-prim/dist-install/build/./autogen -Ilibraries/ghc-prim/. -optP-include -optPlibraries/ghc-prim/dist-install/build/./autogen/cabal_macros.h -package-id rts -this-unit-id ghc-prim -XHaskell2010 -O -dcore-lint -dstg-lint -dcmm-lint -no-user-package-db -rtsopts -Wno-trustworthy-safe -Wno-deprecated-flags -Wnoncanonical-monad-instances -odir libraries/ghc-prim/dist-install/build -hidir libraries/ghc-prim/dist-install/build -stubdir libraries/ghc-prim/dist-install/build -dynamic-too -c libraries/ghc-prim/./GHC/Types.hs -o libraries/ghc-prim/dist-install/build/GHC/Types.o -dyno libraries/ghc-prim/dist-install/build/GHC/Types.dyn_o ghc-stage1: panic! (the 'impossible' happened) (GHC version 126.96.36.19980204 for x86_64-unknown-linux): *** Stg Lint ErrMsgs: in Unarise *** <no location info>: warning: [in body of lambda with binders v_s9Xn :: (a_12 :: k0_10) ~~ (b_13 :: k1_11)] In some algebraic case alternative, number of arguments doesn't match constructor: Eq# (arity 1)  <no location info>: warning: [in body of lambda with binders v_s9Xp :: Coercible a_11 b_12] In some algebraic case alternative, number of arguments doesn't match constructor: MkCoercible (arity 1)  *** Offending Program *** ... lots of lines skipped ... *** End of Offense *** Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/stgSyn/StgLint.hs:68:19 in ghc:StgLint Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug libraries/ghc-prim/ghc.mk:4: recipe for target 'libraries/ghc-prim/dist-install/build/GHC/Types.o' failed
As a side note, it seems that it would be good to enable
devel2 flavour, and possibly some other flavours, or at least on CI, so that they will be tested more frequently.