Type families, holes and -fdefer-type-errors may cause 'opt_univ fell into a hole' panic
This program, when compiled like ghc -fdefer-type-errors -c panic.hs
:
{-# LANGUAGE TypeFamilies #-}
module MorePanic where
transitive :: (a, b) -> (b, c) -> (a, c)
transitive = undefined
trigger :: a -> b -> (F a b, F b a)
trigger _ _ = _ `transitive` trigger _ _
type family F (n :: *) (m :: *) :: *
Gives this panic after several error messages:
ghc.EXE: panic! (the 'impossible' happened)
(GHC version 8.4.3 for x86_64-unknown-mingw32):
opt_univ fell into a hole
{co_a7Sj}
Call stack:
CallStack (from HasCallStack):
callStackDoc, called at compiler\utils\Outputable.hs:1150:37 in ghc:Outputable
pprPanic, called at compiler\\types\\OptCoercion.hs:242:5 in ghc:OptCoercion
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
This bug also affects GHCi. Attached is full output
Trac metadata
Trac field | Value |
---|---|
Version | 8.4.3 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
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Blocking | |
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