id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
4003,tcIfaceGlobal panic building HEAD with 6.12.2,simonmar,igloo,"This is bad, because we can't build HEAD with the newly released 6.12.2.  It was reported a few days ago by Matthias Kilian on cvs-ghc, but at the time we didn't realise it was a regression in 6.12.2.

{{{
ghc: panic! (the 'impossible' happened)
  (GHC version 6.12.2 for x86_64-unknown-linux):
        tcIfaceGlobal (local): not found:
    ghc-6.13:HsExpr.$fxDataHsExpr{v rlO}
    [(a2NS, Identifier `ic{v a2NS}'), (a2O9, Identifier `ic{v a2O9}'),
     (a2Ol, Identifier `ic{v a2Ol}'), (a2OD, Identifier `ic{v a2OD}'),
     (a2OO, Identifier `ic{v a2OO}'), (a2Pj, Identifier `ic{v a2Pj}'),
     (a2Px, Identifier `ic{v a2Px}'), (a2PK, Identifier `ic{v a2PK}'),
     (a2Q6, Identifier `ic{v a2Q6}'), (a2Sf, Identifier `ic{v a2Sf}'),
     (a2Te, Identifier `ic{v a2Te}'), (a2UJ, Identifier `ic{v a2UJ}'),
     (a2WH, Identifier `ic{v a2WH}'), (a35p, Identifier `ic{v a35p}'),
     (a363, Identifier `typeOf1{v a363}'),
     -- more follows
}}}

Unpulling this patch in the HEAD tree allegedly avoids the bug:

{{{
Mon Mar 29 18:10:20 PDT 2010  David Waern <david.waern@gmail.com>
  * Add Data and Typeable instances to HsSyn
}}}
",bug,closed,highest,6.12.3,Compiler,6.12.2,fixed,,pho@…,Unknown/Multiple,Unknown/Multiple,Compile-time crash,,T4003,,,