#14326: Panic on COMPLETE pragma with mismatched type variable order -------------------------------------+------------------------------------- Reporter: dailectic | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: x86_64 Type of failure: Compile-time | (amd64) crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): I feel like you're leaving out some important information here. I tried loading this file (I had to add some language extensions that you left out): {{{#!hs {-# LANGUAGE PatternSynonyms #-} {-# LANGUAGE ScopedTypeVariables #-} module Bug where data E a b = L' a | R b pattern L :: forall b a. a -> E a b pattern L a = L' a {-# COMPLETE L, R #-} }}} I compiled this with 8.2.1, but it did not panic. What am I missing? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14326#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#14326: Panic on COMPLETE pragma with mismatched type variable order -------------------------------------+------------------------------------- Reporter: dailectic | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: x86_64 Type of failure: Compile-time | (amd64) crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by dailectic: Old description:

The motivating example is to allow patterns with phantom types to interact nicely with TypeApplications, so in the below we can do `L @Int :: a -> L a Int` to specify the phantom. {{{#!hs data E a b = L' a | R b pattern L :: forall b a. a -> E a b pattern L a = L' a {-# COMPLETE L, R #-} }}}

Issues occur when nesting cases

{{{ {-# OPTIONS_GHC -fwarn-incomplete-patterns #-} testMono :: E (E Int Int) Int -> Int testMono x = case x of L (L _) -> 0 L (R _) -> 1 R _ -> 2 }}}

And GHC panics when polymorphic

{{{ {-# OPTIONS_GHC -fwarn-incomplete-patterns #-} testPoly :: E (E a b) c -> Int testPoly x = case x of L (L _) -> 0 L (R _) -> 1 R _ -> 2 }}}

The compiler balks

{{{ ghc: panic! (the 'impossible' happened) (GHC version 8.2.1 for x86_64-unknown-linux): mkOneConFull: Not TyConApp: c_a50V Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable pprPanic, called at compiler/deSugar/Check.hs:976:30 in ghc:Check

Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug

}}}

So it seems like there's two related issues here: 1. The COMPLETE pragma does not work in nesting for out-of-order type variables 2. Some printing logic is missing for the error in this polymorphic case

Note that if we define

{{{ pattern L :: forall a b. a -> E a b pattern L a = L' a }}}

Note that we do not get the incomplete warning or the panic, so it seems directly related to the order of the variables, rather than explicit quantification in general

New description: The motivating example is to allow patterns with phantom types to interact nicely with TypeApplications, so in the below we can do `L @Int :: a -> L a Int` to specify the phantom. {{{#!hs {-# LANGUAGE PatternSynonyms #-} {-# LANGUAGE ExplicitForAll #-} data E a b = L' a | R b pattern L :: forall b a. a -> E a b pattern L a = L' a {-# COMPLETE L, R #-} }}} Issues occur when nesting cases {{{ {-# OPTIONS_GHC -fwarn-incomplete-patterns #-} testMono :: E (E Int Int) Int -> Int testMono x = case x of L (L _) -> 0 L (R _) -> 1 R _ -> 2 }}} And GHC panics when polymorphic {{{ {-# OPTIONS_GHC -fwarn-incomplete-patterns #-} testPoly :: E (E a b) c -> Int testPoly x = case x of L (L _) -> 0 L (R _) -> 1 R _ -> 2 }}} The compiler balks {{{ ghc: panic! (the 'impossible' happened) (GHC version 8.2.1 for x86_64-unknown-linux): mkOneConFull: Not TyConApp: c_a50V Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable pprPanic, called at compiler/deSugar/Check.hs:976:30 in ghc:Check Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} So it seems like there's two related issues here: 1. The COMPLETE pragma does not work in nesting for out-of-order type variables 2. Some printing logic is missing for the error in this polymorphic case Note that if we define {{{ pattern L :: forall a b. a -> E a b pattern L a = L' a }}} Note that we do not get the incomplete warning or the panic, so it seems directly related to the order of the variables, rather than explicit quantification in general -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14326#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#14326: Panic on COMPLETE pragma with mismatched type variable order -------------------------------------+------------------------------------- Reporter: dailectic | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: | PatternSynonyms Operating System: Unknown/Multiple | Architecture: x86_64 Type of failure: Compile-time | (amd64) crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * keywords: => PatternSynonyms Comment: Thanks for the update. Interestingly, this does //not// panic on GHC HEAD, which in some ways makes this like an inverse of #14135 (which panics with a `mkOneConFull` error on HEAD, but not 8.2.1). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14326#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#14326: Panic on COMPLETE pragma with mismatched type variable order -------------------------------------+------------------------------------- Reporter: dailectic | Owner: RyanGlScott Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: | PatternSynonyms Operating System: Unknown/Multiple | Architecture: x86_64 Type of failure: Compile-time | (amd64) crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ryan Scott ): In [changeset:"429fafb5b2b1ac02fd04d9a98e30b5991125692c/ghc" 429fafb5/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="429fafb5b2b1ac02fd04d9a98e30b5991125692c" Add regression test for #14326 Commit 6b77914cd37b697354611bcd87897885c1e5b4a6 wound up fixing #14326. Let's add a regression test so that it stays that way. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14326#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler