panic: lookupVers1, when standalone deriving Typeable and Data

When using !StandaloneDeriving and !DeriveDataTypeable on a rather large AST, occasionally GHC 6.8.2 and GHC 6.8.3 RC bail with

[13 of 24] Compiling Language.C.AST.Generic
...
ghc-6.8.2.20080527: panic! (the 'impossible' happened)
  (GHC version 6.8.2.20080527 for i386-apple-darwin):
        lookupVers1 language-c-test-0.2:Language.C.AST.Constants $cFlags{v}

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

This is probably related to ticket #2011 (closed) (marked as milestone 6.8.3), clean and rebuild resolves the problem temporarily.

I haven't been able to extract a small test case, but the problematic source is available online at

http://code.haskell.org/language-c/src/Language/C/AST/Generic.hs

The bug is reproducible: (cabal) build, comment out the last 6 'deriving Data' clauses (line 96-101), build again, uncomment, build again.

Side notes: There is a warning (but no error !) when deriving a Typeable1 instance (maybe related to #1825 (closed))

[13 of 24] Compiling Language.C.AST.Generic
Var/Type length mismatch: 
    [f{tv i1lc} [tv]]
    []
... [as above]

Finally, in GHC 6.9 standalone deriving Data was unsupported as of 01042008:

[13 of 24] Compiling Language.C.AST.Generic
Illegal binding of built-in syntax: $cCHeader

Trac metadata

Trac field	Value
Version	6.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	benedikt.huber@gmail.com
Operating system
Architecture