#14732: -fdefer-type-holes breaks a correct program -------------------------------------+------------------------------------- Reporter: MitchellSalad | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by MitchellSalad: Old description:

Here's a bug I discovered in `vector` that Ryan Scott identified as a regression from 7.10.3:

https://github.com/haskell/vector/issues/200

Here is Ryan's minimal example:

{{{#!hs

{-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE KindSignatures #-} {-# LANGUAGE MultiParamTypeClasses #-} module Bug where

import Prelude hiding (zip, zipWith)

zipWith :: (a -> b -> c) -> Bundle v a -> Bundle v b -> Bundle v c zipWith = undefined

class GVector (v :: * -> *) a instance GVector Vector a

data Bundle (v :: * -> *) a data Vector a class Unbox a

stream :: GVector v a => v a -> Bundle v a {-# INLINE [1] stream #-} stream = undefined

zip :: (Unbox a, Unbox b) => Vector a -> Vector b -> Vector (a, b) {-# INLINE [1] zip #-} zip = undefined {-# RULES "stream/zip [Vector.Unboxed]" forall as bs . stream (zip as bs) = zipWith (,) (stream as) (stream bs) #-}{#!hs

}}}

Output (8.2.2):

{{{ Bug.hs:29:11: error: • Could not deduce (Unbox a) arising from a use of ‘zip’ from the context: GVector Vector (a, b) bound by the RULE "stream/zip [Vector.Unboxed]" at Bug.hs:(28,11)-(30,46) Possible fix: add (Unbox a) to the context of the RULE "stream/zip [Vector.Unboxed]" • In the first argument of ‘stream’, namely ‘(zip as bs)’ In the expression: stream (zip as bs) When checking the transformation rule "stream/zip [Vector.Unboxed]" | 29 | stream (zip as bs) = zipWith (,) (stream as) | ^^^^^^^^^ }}}

Similar output in 8.0.1, 8.0.2, 8.2.1

New description: Here's a bug I discovered in `vector` that Ryan Scott identified as a regression from 7.10.3: https://github.com/haskell/vector/issues/200 Here is Ryan's minimal example: {{{#!hs {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE KindSignatures #-} {-# LANGUAGE MultiParamTypeClasses #-} module Bug where import Prelude hiding (zip, zipWith) zipWith :: (a -> b -> c) -> Bundle v a -> Bundle v b -> Bundle v c zipWith = undefined class GVector (v :: * -> *) a instance GVector Vector a data Bundle (v :: * -> *) a data Vector a class Unbox a stream :: GVector v a => v a -> Bundle v a {-# INLINE [1] stream #-} stream = undefined zip :: (Unbox a, Unbox b) => Vector a -> Vector b -> Vector (a, b) {-# INLINE [1] zip #-} zip = undefined {-# RULES "stream/zip [Vector.Unboxed]" forall as bs . stream (zip as bs) = zipWith (,) (stream as) (stream bs) #-} }}} Output (8.2.2): {{{ Bug.hs:29:11: error: • Could not deduce (Unbox a) arising from a use of ‘zip’ from the context: GVector Vector (a, b) bound by the RULE "stream/zip [Vector.Unboxed]" at Bug.hs:(28,11)-(30,46) Possible fix: add (Unbox a) to the context of the RULE "stream/zip [Vector.Unboxed]" • In the first argument of ‘stream’, namely ‘(zip as bs)’ In the expression: stream (zip as bs) When checking the transformation rule "stream/zip [Vector.Unboxed]" | 29 | stream (zip as bs) = zipWith (,) (stream as) | ^^^^^^^^^ }}} Similar output in 8.0.1, 8.0.2, 8.2.1 -- -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14732#comment:1> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

#14732: -fdefer-typed-holes breaks a correct program -------------------------------------+------------------------------------- Reporter: MitchellSalad | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): What exactly is the bug here, and how can I reproduce it? What has it got to do with `-fdefer-type-errors`? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14732#comment:3> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

#14732: -fdefer-typed-holes breaks a correct program -------------------------------------+------------------------------------- Reporter: MitchellSalad | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones <simonpj@…>): In [changeset:"e9ae0cae9eb6a340473b339b5711ae76c6bdd045/ghc" e9ae0ca/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="e9ae0cae9eb6a340473b339b5711ae76c6bdd045" Look inside implications in simplifyRule Trac #14732 was a perpelexing bug in which -fdefer-typed-holes caused a mysterious type error in a RULE. This turned out to be because we are more aggressive about creating implications when deferring (see TcUnify.implicationNeeded), and the rule mechanism hadn't caught up. This fixes it. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14732#comment:5> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

#14732: -fdefer-typed-holes breaks a correct program -------------------------------------+------------------------------------- Reporter: MitchellSalad | Owner: (none) Type: bug | Status: merge Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.2.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | typecheck/should_compile/T14732 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * milestone: => 8.4.1 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14732#comment:7> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler