[GHC] #15276: Bogus type in typechecker error recovery
#15276: Bogus type in typechecker error recovery -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- If the typechecker sees {{{ let f = <rhs> in <body> }}} and there's a type error in `<rhs>`, GHC recovers from the error, binds `f` to "a type that should cause no more trouble", and continues with `<both>` in the hope of finding more type errors. What is "a type that should cause no more trouble"? Well `forall a.a` seems like a good candidate. But, in this commit {{{ commit 6746549772c5cc0ac66c0fce562f297f4d4b80a2 Author: Richard Eisenberg <eir@cis.upenn.edu> Date: Fri Dec 11 18:19:53 2015 -0500 Add kind equalities to GHC. }}} we made the type look like this: `forall r. forall (a :: TYPE r). a` Alas! That type is ill-formed because the kind `TYPE r` escapes the scope of `f`. I discovered this when beefing up `typeKind` in pursuit of #14939 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15276> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler
#15276: Bogus type in typechecker error recovery -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 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 Simon Peyton Jones <simonpj@…>): In [changeset:"807ab222d08c11a4d00064c9835f9ed9f20ffc7c/ghc" 807ab22/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="807ab222d08c11a4d00064c9835f9ed9f20ffc7c" Fix the bind-recovery type This patch uses (forall (a::*). a) for the type to use when recovering from an error in a binding. Previously (Trac #15276) we had (forall r (a :: TYPE r). a), which is ill-kinded. It's quite hard to provoke an error arising from this, because it only happens in programs that have a type error anyway, but in a subequent patch I make typeKind fall over if it returns an ill-scoped kind, and that makes ghci/scripts/T13202 crash without this fix. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15276#comment:1> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler
#15276: Bogus type in typechecker error recovery -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Resolution: fixed | 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: | -------------------------------------+------------------------------------- Changes (by simonpj): * status: new => closed * resolution: => fixed -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15276#comment:2> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler
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