#16342: Kind inference crash -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 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:

Here's a gnarly test case {{{ {-# LANGUAGE MultiParamTypeClasses, TypeInType, ConstrainedClassMethods, ScopedTypeVariables #-}

module Foo where

import Data.Proxy

class C (a::ka) x where cop :: D a x => x -> Proxy a -> Proxy a cop _ x = x :: Proxy (a::ka)

class D (b::kb) y where dop :: C b y => y -> Proxy b -> Proxy b dop _ x = x :: Proxy (b::kb) }}} This crashes every recent GHC with {{{ • GHC internal error: ‘kb’ is not in scope during type checking, but it passed the renamer tcl_env of environment: [avu :-> Type variable ‘b’ = b :: ka, avv :-> Type variable ‘y’ = y :: *, avw :-> Identifier[x::Proxy b, NotLetBound], avx :-> Type variable ‘ka’ = ka :: *] • In the kind ‘kb’ In the first argument of ‘Proxy’, namely ‘(b :: kb)’ In an expression type signature: Proxy (b :: kb) | 13 | dop _ x = x :: Proxy (b::kb) | ^^ }}} Yikes.

Reason: * `C` and `D` are mutually recursive * `ka` and `kb` get bound to unification variables, and then get unified in the kind-inference phase * As a result the utterly-final class for `C` and `D` end up with the same `TyVar` for `ka`/`kb`. * And then, for one of them, the tyvar is not in scope when (much, much later) we check the default declaration.

Gah! In `generaliseTcTyCon` I think we may need to do a reverse-map to ensure that each of the final `tyConTyVars` has the `Name` from this declaration, rather than accidentally getting a `Name` from another decl in the mutually recursive group.

New description: Here's a gnarly test case {{{ {-# LANGUAGE MultiParamTypeClasses, TypeInType, ConstrainedClassMethods, ScopedTypeVariables #-} module Foo where import Data.Proxy class C (a::ka) x where cop :: D a x => x -> Proxy a -> Proxy a cop _ x = x :: Proxy (a::ka) class D (b::kb) y where dop :: C b y => y -> Proxy b -> Proxy b dop _ x = x :: Proxy (b::kb) }}} This crashes every recent GHC outright, with {{{ • GHC internal error: ‘kb’ is not in scope during type checking, but it passed the renamer tcl_env of environment: [avu :-> Type variable ‘b’ = b :: ka, avv :-> Type variable ‘y’ = y :: *, avw :-> Identifier[x::Proxy b, NotLetBound], avx :-> Type variable ‘ka’ = ka :: *] • In the kind ‘kb’ In the first argument of ‘Proxy’, namely ‘(b :: kb)’ In an expression type signature: Proxy (b :: kb) | 13 | dop _ x = x :: Proxy (b::kb) | ^^ }}} Yikes. Reason: * `C` and `D` are mutually recursive * `ka` and `kb` get bound to unification variables, and then get unified in the kind-inference phase * As a result the utterly-final class for `C` and `D` end up with the same `TyVar` for `ka`/`kb`. * And then, for one of them, the tyvar is not in scope when (much, much later) we check the default declaration. Gah! In `generaliseTcTyCon` I think we may need to do a reverse-map to ensure that each of the final `tyConTyVars` has the `Name` from this declaration, rather than accidentally getting a `Name` from another decl in the mutually recursive group. -- -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16342#comment:1> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

#16342: Kind inference crash -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 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): If we type-checked `HsDecl GhcRn` into `HsDecl GhcTc`, this would be much easier. Of course, classes get type-checked in pieces, so we would need multiple phase parameters there... In any case, I agree that reverse-mapping may be the cheap and cheerful solution here. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16342#comment:3> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

#16342: Kind inference crash -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #16221 | Differential Rev(s): Wiki Page: | https://gitlab.haskell.org/ghc/ghc/merge_requests/444 -------------------------------------+------------------------------------- Comment (by Marge Bot <ben+marge-bot@…>): In [changeset:"80dfcee61e3bfb67f131cd674f96467e16c0f9d8/ghc" 80dfcee6/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="80dfcee61e3bfb67f131cd674f96467e16c0f9d8" Be more careful when naming TyCon binders This patch fixes two rather gnarly test cases: * Trac #16342 (mutual recursion) See Note [Tricky scoping in generaliseTcTyCon] * Trac #16221 (shadowing) See Note [Unification variables need fresh Names] The main changes are: * Substantial reworking of TcTyClsDecls.generaliseTcTyCon This is the big change, and involves the rather tricky function TcHsSyn.zonkRecTyVarBndrs. See Note [Inferring kinds for type declarations] and Note [Tricky scoping in generaliseTcTyCon] for the details. * bindExplicitTKBndrs_Tv and bindImplicitTKBndrs_Tv both now allocate /freshly-named/ unification variables. Indeed, more generally, unification variables are always fresh; see Note [Unification variables need fresh Names] in TcMType * Clarify the role of tcTyConScopedTyVars. See Note [Scoped tyvars in a TcTyCon] in TyCon As usual, this dragged in some more refactoring: * Renamed TcMType.zonkTyCoVarBndr to zonkAndSkolemise * I renamed checkValidTelescope to checkTyConTelescope; it's only used on TyCons, and indeed takes a TyCon as argument. * I folded the slightly-mysterious reportFloatingKvs into checkTyConTelescope. (Previously all its calls immediately followed a call to checkTyConTelescope.) It makes much more sense there. * I inlined some called-once functions to simplify checkValidTyFamEqn. It's less spaghetti-like now. * This patch also fixes Trac #16251. I'm not quite sure why #16251 went wrong in the first place, nor how this patch fixes it, but hey, it's good, and life is short. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16342#comment:5> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

#16342: Kind inference crash -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.10.1 Component: Compiler | Version: 8.6.3 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #16221 | Differential Rev(s): | https://gitlab.haskell.org/ghc/ghc/merge_requests/444, Wiki Page: | https://gitlab.haskell.org/ghc/ghc/merge_requests/499 -------------------------------------+------------------------------------- Changes (by simonpj): * status: patch => closed * resolution: => fixed Comment: Test landed as {{{ commit 07f378cee37338c5f2655b3a7e46dfef3f1c5cc1 Author: Simon Peyton Jones <simonpj@microsoft.com> Date: Wed Mar 6 09:54:06 2019 +0000 Add tests for Trac #16221 and #16342 testsuite/tests/polykinds/T16221.hs | 13 +++++++++++++ testsuite/tests/polykinds/T16221a.hs | 7 +++++++ testsuite/tests/polykinds/T16221a.stderr | 6 ++++++ testsuite/tests/polykinds/T16342.hs | 13 +++++++++++++ testsuite/tests/polykinds/all.T | 3 +++ 5 files changed, 42 insertions(+) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16342#comment:7> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler