#14066: Skolem escape at the kind level -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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 simonpj: Old description:

This program should be rejected {{{ {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE TypeInType #-} {-# LANGUAGE KindSignatures #-}

module Foo2 where

import Data.Kind ( Type )

import Data.Type.Equality

import Data.Proxy

import GHC.Exts

data SameKind :: k -> k -> Type

f (x :: Proxy a) = let g :: forall k (b :: k). SameKind a b

g = undefined

in

() }}} But

* 8.0 rejects it, with an unhelpful message

* 8.2 accepts it, and the result satisfies Core Lint

* HEAD accepts it, and produces a Core Lint Error

New description: This program should be rejected {{{ {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE TypeInType #-} {-# LANGUAGE KindSignatures #-} module Foo2 where import Data.Kind ( Type ) import Data.Type.Equality import Data.Proxy import GHC.Exts data SameKind :: k -> k -> Type f (x :: Proxy a) = let g :: forall k (b :: k). SameKind a b g = undefined in () }}} But * 8.0 rejects it, with an unhelpful message * 8.2 accepts it, and the result satisfies Core Lint * HEAD accepts it, and produces a Core Lint Error -- -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14066#comment:1> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

#14066: Skolem escape at the kind level -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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): Fixing this will probably cure #14040. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14066#comment:3> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

#14066: Skolem escape at the kind level -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 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 goldfire): This is a dup of #13364. But this one has more commentary, so keeping this one. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14066#comment:5> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

#14066: Skolem escape at the kind level -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #13364, #14040 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * related: => #13364, #14040 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14066#comment:7> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

#14066: Skolem escape at the kind level -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #13364, #14040 | Differential Rev(s): Wiki Page: | https://ghc.haskell.org/trac/ghc/wiki/GhcKinds/KindInference| -------------------------------------+------------------------------------- Comment (by Richard Eisenberg <rae@…>): In [changeset:"faec8d358985e5d0bf363bd96f23fe76c9e281f7/ghc" faec8d35/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="faec8d358985e5d0bf363bd96f23fe76c9e281f7" Track type variable scope more carefully. The main job of this commit is to track more accurately the scope of tyvars introduced by user-written foralls. For example, it would be to have something like this: forall a. Int -> (forall k (b :: k). Proxy '[a, b]) -> Bool In that type, a's kind must be k, but k isn't in scope. We had a terrible way of doing this before (not worth repeating or describing here, but see the old tcImplicitTKBndrs and friends), but now we have a principled approach: make an Implication when kind-checking a forall. Doing so then hooks into the existing machinery for preventing skolem-escape, performing floating, etc. This also means that we bump the TcLevel whenever going into a forall. The new behavior is done in TcHsType.scopeTyVars, but see also TcHsType.tc{Im,Ex}plicitTKBndrs, which have undergone significant rewriting. There are several Notes near there to guide you. Of particular interest there is that Implication constraints can now have skolems that are out of order; this situation is reported in TcErrors. A major consequence of this is a slightly tweaked process for type- checking type declarations. The new Note [Use SigTvs in kind-checking pass] in TcTyClsDecls lays it out. The error message for dependent/should_fail/TypeSkolEscape has become noticeably worse. However, this is because the code in TcErrors goes to some length to preserve pre-8.0 error messages for kind errors. It's time to rip off that plaster and get rid of much of the kind-error-specific error messages. I tried this, and doing so led to a lovely error message for TypeSkolEscape. So: I'm accepting the error message quality regression for now, but will open up a new ticket to fix it, along with a larger error-message improvement I've been pondering. This applies also to dependent/should_fail/{BadTelescope2,T14066,T14066e}, polykinds/T11142. Other minor changes: - isUnliftedTypeKind didn't look for tuples and sums. It does now. - check_type used check_arg_type on both sides of an AppTy. But the left side of an AppTy isn't an arg, and this was causing a bad error message. I've changed it to use check_type on the left-hand side. - Some refactoring around when we print (TYPE blah) in error messages. The changes decrease the times when we do so, to good effect. Of course, this is still all controlled by -fprint-explicit-runtime-reps Fixes #14066 #14749 Test cases: dependent/should_compile/{T14066a,T14749}, dependent/should_fail/T14066{,c,d,e,f,g,h} }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14066#comment:9> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler