[GHC] #14127: -fignore-interface-pragmas and -fspecialise do not go well together

[GHC]

#14127: -fignore-interface-pragmas and -fspecialise do not go well together
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        Reporter:  lspitzner         |                Owner:  (none)
            Type:  bug               |               Status:  infoneeded
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by lspitzner):

 Sorry, I wrongly assumed this was much easier to reproduce. Now that I
 try, it appears to be pretty specific, in fact I can't even simplify
 properly. This still needs a dependency on aeson-1.2.1.0:

 - A.hs
 {{{#!hs
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE DeriveDataTypeable #-}

 module A where

 import GHC.Generics

 data Foo = AltChooserSimpleQuick
   deriving (Generic)

 }}}

 - B.hs
 {{{#!hs
 {-# OPTIONS_GHC -fno-pre-inlining #-}
 {-# OPTIONS_GHC -fspecialise #-}
 {-# OPTIONS_GHC -fignore-interface-pragmas #-}

 module B where

 import A
 import qualified Data.Aeson.Types as Aeson

 instance Aeson.FromJSON Foo where
   parseJSON = Aeson.genericParseJSON Aeson.defaultOptions
   {-# NOINLINE parseJSON #-}

 }}}

 I have made several attempts to reproduce this with a standalone class
 instead of the one from aeson, but failed to do so. It also appears that
 the panic disappears when there is no orphan instance in play (i.e. if you
 merge modules A/B).

 Also note that simply replacing `data Foo = AltChooseSimpleQuick` with
 `data Foo = AltChoose` the panic disappears. Further testing suggests that
 it requires any constructor identifier with at least 21 characters to
 trigger the panic.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14127#comment:2>
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