[GHC] #13381: "opt_univ fell into a hole" panic from rewrite rule
#13381: "opt_univ fell into a hole" panic from rewrite rule -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Roboguy reports (via IRC) that the following causes a GHC panic: {{{#!hs {-# LANGUAGE RankNTypes #-} module Crash where data Exp a = Exp fromExp :: Exp a -> a fromExp _ = error "Impossible" toExp :: a -> Exp a toExp _ = Exp newtype Iter a b = Iter { getIter :: forall r. (a -> r) -> (b -> r) -> r } iterLoop :: (a -> Iter a b) -> a -> b iterLoop f x = getIter (f x) (iterLoop f) id -- This rewrite rule results in a GHC panic: "opt_univ fell into a hole" on GHC 8.0.1, 8.0.2, and 8.1. {-# RULES "fromExp-into-iterLoop" [~] forall (f :: Int -> Iter (Exp Int) (Exp Char)) (init :: Int). fromExp (iterLoop f init) = fromExp (iterLoop (f . fromExp) (toExp init)) #-} }}} I have confirmed this, and see the following error: {{{ ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.1.20170305 for x86_64-unknown-linux): opt_univ fell into a hole {a1WD} Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1191:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1195:37 in ghc:Outputable pprPanic, called at compiler/types/OptCoercion.hs:398:29 in ghc:OptCoercion }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13381 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13381: "opt_univ fell into a hole" panic from rewrite rule -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): To make things even more interesting, this error does not occur on GHC 7.8 or 7.10. Here's the error you get with 7.10.3: {{{ GHCi, version 7.10.3: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Crash ( Bug.hs, interpreted ) Bug.hs:25:23: Couldn't match type ‘Exp Int’ with ‘Int’ Expected type: Exp Int -> Iter (Exp Int) (Exp Char) Actual type: Int -> Iter (Exp Int) (Exp Char) In the first argument of ‘iterLoop’, namely ‘f’ In the first argument of ‘fromExp’, namely ‘(iterLoop f init)’ Bug.hs:25:25: Couldn't match expected type ‘Exp Int’ with actual type ‘Int’ In the second argument of ‘iterLoop’, namely ‘init’ In the first argument of ‘fromExp’, namely ‘(iterLoop f init)’ }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13381#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13381: "opt_univ fell into a hole" panic from rewrite rule -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * cc: goldfire (added) Comment: Commit 6746549772c5cc0ac66c0fce562f297f4d4b80a2 (Add kind equalities to GHC) introduced this regression. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13381#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13381: "opt_univ fell into a hole" panic from rewrite rule -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): To be clear, the `opt_univ fell into a hole` bit is a red herring here. The real problem is that the type-checker doesn't reject the program. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13381#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13381: "opt_univ fell into a hole" panic from rewrite rule
-------------------------------------+-------------------------------------
Reporter: dfeuer | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone: 8.2.1
Component: Compiler | Version: 8.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
Type of failure: Compile-time | Unknown/Multiple
crash or panic | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
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Comment (by Simon Peyton Jones
#13381: "opt_univ fell into a hole" panic from rewrite rule -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.1 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Compile-time | Test Case: crash or panic | typecheck/should_compile/T13381 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * status: new => closed * testcase: => typecheck/should_compile/T13381 * resolution: => fixed -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13381#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13381: "opt_univ fell into a hole" panic from rewrite rule -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.1 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Compile-time | Test Case: crash or panic | typecheck/should_compile/T13381 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): Merged to `ghc-8.2` as 98692134c3aee35dd89992aff3c350f49543a67b -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13381#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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