Impossible when deriving empty data declaration

When trying to load following code into GHCi I get an error:

ghc: panic! (the 'impossible' happened)
  (GHC version 6.12.3 for x86_64-unknown-linux):
	TcGenDeriv:mk_FunBind

Code is:

{-# LANGUAGE StandaloneDeriving, EmptyDataDecls #-}
module Test where
data Test
deriving instance Show (Test)

Probably Test cannot be made instance of Show but still error should be less fatal. ;-)

Trac metadata

Trac field	Value
Version	6.12.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	mmitar@gmail.com
Operating system
Architecture

mentioned in issue #4220 (closed)

changed weight to 5

added Tbug Trac import labels

changed milestone to %7.2.1

Thanks for the report.

mentioned in commit 2fc5aa70

mentioned in commit 7b5674ce

closed

Excellent point. This is really the same bug as #4220 (closed), but needs a more systematic fix. Done with

Mon Sep 13 18:03:55 BST 2010  simonpj@microsoft.com
  * Fix Trac #4302, plus a little refactoring

    M ./compiler/hsSyn/HsUtils.lhs -13 +1
    M ./compiler/typecheck/TcDeriv.lhs -12 +19
    M ./compiler/typecheck/TcGenDeriv.lhs -28 +48

And I added another test

Simon

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed
Test case	→ deriving/should_compile/T4302

mentioned in issue #5628 (closed)

mentioned in issue #8204 (closed)

commit 2fc5aa70

Author: simonpj@microsoft.com <unknown>
Date:   Mon Sep 13 17:03:55 2010 +0000

    Fix Trac #4302, plus a little refactoring

added Pnormal label