GHC 8.0.2-9448e62: Couldn't match type ‘m’ with ‘StateT s m’

[ilovezfs]

purescript 0.10.2 build failure with GHC pre-8.0.2-9448e62 (ghc/ghc@9448e62).

Building purescript-0.10.2...
Preprocessing library purescript-0.10.2...
[  1 of 139] Compiling System.IO.UTF8   ( src/System/IO/UTF8.hs, dist/dist-sandbox-4bbb699a/build/System/IO/UTF8.o )
[  2 of 139] Compiling Paths_purescript ( dist/dist-sandbox-4bbb699a/build/autogen/Paths_purescript.hs, dist/dist-sandbox-4bbb699a/build/Paths_purescript.o )
[  3 of 139] Compiling Language.PureScript.Traversals ( src/Language/PureScript/Traversals.hs, dist/dist-sandbox-4bbb699a/build/Language/PureScript/Traversals.o )
[  4 of 139] Compiling Language.PureScript.Publish.Utils ( src/Language/PureScript/Publish/Utils.hs, dist/dist-sandbox-4bbb699a/build/Language/PureScript/Publish/Utils.o )
[  5 of 139] Compiling Language.PureScript.Publish.BoxesHelpers ( src/Language/PureScript/Publish/BoxesHelpers.hs, dist/dist-sandbox-4bbb699a/build/Language/PureScript/Publish/BoxesHelpers.o )
[  6 of 139] Compiling Language.PureScript.Parser.State ( src/Language/PureScript/Parser/State.hs, dist/dist-sandbox-4bbb699a/build/Language/PureScript/Parser/State.o )
[  7 of 139] Compiling Language.PureScript.Options ( src/Language/PureScript/Options.hs, dist/dist-sandbox-4bbb699a/build/Language/PureScript/Options.o )
[  8 of 139] Compiling Language.PureScript.Kinds ( src/Language/PureScript/Kinds.hs, dist/dist-sandbox-4bbb699a/build/Language/PureScript/Kinds.o )
[  9 of 139] Compiling Language.PureScript.Interactive.IO ( src/Language/PureScript/Interactive/IO.hs, dist/dist-sandbox-4bbb699a/build/Language/PureScript/Interactive/IO.o )
[ 10 of 139] Compiling Language.PureScript.Docs.Utils.MonoidExtras ( src/Language/PureScript/Docs/Utils/MonoidExtras.hs, dist/dist-sandbox-4bbb699a/build/Language/PureScript/Docs/Utils/MonoidExtras.o )
[ 11 of 139] Compiling Language.PureScript.Crash ( src/Language/PureScript/Crash.hs, dist/dist-sandbox-4bbb699a/build/Language/PureScript/Crash.o )
[ 12 of 139] Compiling Language.PureScript.Comments ( src/Language/PureScript/Comments.hs, dist/dist-sandbox-4bbb699a/build/Language/PureScript/Comments.o )
[ 13 of 139] Compiling Language.PureScript.Parser.Lexer ( src/Language/PureScript/Parser/Lexer.hs, dist/dist-sandbox-4bbb699a/build/Language/PureScript/Parser/Lexer.o )
[ 14 of 139] Compiling Language.PureScript.Bundle ( src/Language/PureScript/Bundle.hs, dist/dist-sandbox-4bbb699a/build/Language/PureScript/Bundle.o )

src/Language/PureScript/Bundle.hs:535:5: warning: [-Wincomplete-patterns]
    Pattern match(es) are non-exhaustive
    In an equation for ‘squash’: Patterns not matched: JSAnnotSpace

src/Language/PureScript/Bundle.hs:590:7: warning: [-Wincomplete-patterns]
    Pattern match(es) are non-exhaustive
    In an equation for ‘appendAnn’:
        Patterns not matched: _ JSAnnotSpace
[ 15 of 139] Compiling Language.PureScript.AST.SourcePos ( src/Language/PureScript/AST/SourcePos.hs, dist/dist-sandbox-4bbb699a/build/Language/PureScript/AST/SourcePos.o )
[ 16 of 139] Compiling Language.PureScript.AST.Operators ( src/Language/PureScript/AST/Operators.hs, dist/dist-sandbox-4bbb699a/build/Language/PureScript/AST/Operators.o )
[ 17 of 139] Compiling Language.PureScript.AST.Literals ( src/Language/PureScript/AST/Literals.hs, dist/dist-sandbox-4bbb699a/build/Language/PureScript/AST/Literals.o )
[ 18 of 139] Compiling Control.Monad.Supply ( src/Control/Monad/Supply.hs, dist/dist-sandbox-4bbb699a/build/Control/Monad/Supply.o )
[ 19 of 139] Compiling Control.Monad.Supply.Class ( src/Control/Monad/Supply/Class.hs, dist/dist-sandbox-4bbb699a/build/Control/Monad/Supply/Class.o )

src/Control/Monad/Supply/Class.hs:30:10: error:
    • Couldn't match type ‘m’ with ‘StateT s m’
      ‘m’ is a rigid type variable bound by
        the instance declaration at src/Control/Monad/Supply/Class.hs:30:10
      Expected type: StateT s m Integer
        Actual type: StateT s (StateT s m) Integer
    • In the expression:
        Control.Monad.Supply.Class.$dmfresh @StateT s m
      In an equation for ‘fresh’:
          fresh = Control.Monad.Supply.Class.$dmfresh @StateT s m
      In the instance declaration for ‘MonadSupply (StateT s m)’
    • Relevant bindings include
        fresh :: StateT s m Integer
          (bound at src/Control/Monad/Supply/Class.hs:30:10)

src/Control/Monad/Supply/Class.hs:30:10: error:
    • Couldn't match type ‘m’ with ‘StateT s m’
      ‘m’ is a rigid type variable bound by
        the instance declaration at src/Control/Monad/Supply/Class.hs:30:10
      Expected type: StateT s m Integer
        Actual type: StateT s (StateT s m) Integer
    • In the expression: Control.Monad.Supply.Class.$dmpeek @StateT s m
      In an equation for ‘peek’:
          peek = Control.Monad.Supply.Class.$dmpeek @StateT s m
      In the instance declaration for ‘MonadSupply (StateT s m)’
    • Relevant bindings include
        peek :: StateT s m Integer
          (bound at src/Control/Monad/Supply/Class.hs:30:10)

src/Control/Monad/Supply/Class.hs:31:10: error:
    • Couldn't match type ‘m’ with ‘WriterT w m’
      ‘m’ is a rigid type variable bound by
        the instance declaration at src/Control/Monad/Supply/Class.hs:31:10
      Expected type: WriterT w m Integer
        Actual type: WriterT w (WriterT w m) Integer
    • In the expression:
        Control.Monad.Supply.Class.$dmfresh @WriterT w m
      In an equation for ‘fresh’:
          fresh = Control.Monad.Supply.Class.$dmfresh @WriterT w m
      In the instance declaration for ‘MonadSupply (WriterT w m)’
    • Relevant bindings include
        fresh :: WriterT w m Integer
          (bound at src/Control/Monad/Supply/Class.hs:31:10)

src/Control/Monad/Supply/Class.hs:31:10: error:
    • Couldn't match type ‘m’ with ‘WriterT w m’
      ‘m’ is a rigid type variable bound by
        the instance declaration at src/Control/Monad/Supply/Class.hs:31:10
      Expected type: WriterT w m Integer
        Actual type: WriterT w (WriterT w m) Integer
    • In the expression:
        Control.Monad.Supply.Class.$dmpeek @WriterT w m
      In an equation for ‘peek’:
          peek = Control.Monad.Supply.Class.$dmpeek @WriterT w m
      In the instance declaration for ‘MonadSupply (WriterT w m)’
    • Relevant bindings include
        peek :: WriterT w m Integer
          (bound at src/Control/Monad/Supply/Class.hs:31:10)
cabal: Leaving directory '.'
cabal: Error: some packages failed to install:
purescript-0.10.2 failed during the building phase. The exception was:
ExitFailure 1

Full build log: https://bot.brew.sh/job/Homebrew%20Core/10983/version=any_sierra/consoleText

(link will eventually die, so duplicated here: https://gist.githubusercontent.com/ilovezfs/fb1c282b2a123e23d480882e74f74db4/raw/24f75f77fa0922d593ec58df7a6787314a9c54e8/gistfile1.txt)

[ilovezfs]

Note that this is a bug in purescript, not GHC, and it's basically the same problem as kazu-yamamoto/logger#106 was, which was fixed in kazu-yamamoto/logger#108. See the discussion in https://ghc.haskell.org/trac/ghc/ticket/12784 for additional information.

[ilovezfs]

The release notes for 8.0.2 will mention the situation: https://phabricator.haskell.org/D2682 since downstream projects will be expected to correct their types.

rwbarton has identified the problematic bits in purescript here: https://ghc.haskell.org/trac/ghc/ticket/12784#comment:11

And the relevant code (excerpted from ​https://github.com/purescript/purescript/blob/master/src/Control/Monad/Supply/Class.hs):

class Monad m => MonadSupply m where
  fresh :: m Integer
  peek :: m Integer
  default fresh :: MonadTrans t => t m Integer
  fresh = lift fresh
  default peek :: MonadTrans t => t m Integer
  peek = lift peek

instance MonadSupply m => MonadSupply (StateT s m)
instance (Monoid w, MonadSupply m) => MonadSupply (WriterT w m)