[GHC] #5424: Validate error under 7.2.1 caused by incomplete pattern warnings in new code gen (GADTs)

[GHC]

#5424: Validate error under 7.2.1 caused by incomplete pattern warnings in new
code gen (GADTs)
---------------------------------+------------------------------------------
    Reporter:  dterei            |        Owner:  simonpj            
        Type:  bug               |       Status:  new                
    Priority:  normal            |    Milestone:                     
   Component:  Compiler          |      Version:  7.2.1              
    Keywords:                    |     Testcase:                     
   Blockedby:                    |   Difficulty:                     
          Os:  Unknown/Multiple  |     Blocking:                     
Architecture:  Unknown/Multiple  |      Failure:  Building GHC failed
---------------------------------+------------------------------------------

Comment(by simonpj@…):

 commit de9b85fa3fb6d4cd593366e1f2383cd0b492c056
 {{{
 Author: Simon Peyton Jones <simonpj at microsoft.com>
 Date:   Fri Sep 2 17:43:53 2011 +0100

     Export a tiny bit more info with AbstractTyCon (fixes #5424)

     When we compile -O0 we put type constructors in the interface file
     without their data constructors -- an AbstractTyCon.  But in a
     client module, to give good pattern-match exhaustiveness warnings,
     we need to know the difference between a data type and a newtype.
     (The latter can be coerced to another type, but a data type can't.)
     See Note [Pruning dead case alternatives] in Unify.

     Because we weren't conveying this info, we were getting bogus
     warnings about inexhaustive patterm matches with GADTs, and
     (confusingly) these warnings woudl come and go depending on
     whether you were compiling with -O.

     This patch makes AbstractTyCon carry a flag indicating whether
     the type constructor is "distinct"; two distinct TyCons cannot
     be coerced into eachother (except by unsafeCoerce, in which case
     all bets are off).

     HEADS UP: interface file format changes slightly, so you need
     to make clean.

  compiler/iface/BinIface.hs          |    4 +-
  compiler/iface/BuildTyCl.lhs        |    7 ++--
  compiler/iface/IfaceSyn.lhs         |   24 +++++++-------
  compiler/iface/MkIface.lhs          |    2 +-
  compiler/iface/TcIface.lhs          |    2 +-
  compiler/typecheck/TcDeriv.lhs      |    2 +-
  compiler/typecheck/TcRnDriver.lhs   |    4 ++-
  compiler/typecheck/TcTyClsDecls.lhs |    4 +-
  compiler/types/TyCon.lhs            |   57
 +++++++++++++++++++++++++++-------
  compiler/types/Unify.lhs            |   10 +++---
  10 files changed, 76 insertions(+), 40 deletions(-)
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5424#comment:3>
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