[GHC] #12027: ghc 8.0rc4 treats INLINE pragmas for methods with default (implicit) definitions as errors

[GHC]

#12027: ghc 8.0rc4 treats INLINE pragmas for methods with default (implicit)
definitions as errors
-------------------------------------+-------------------------------------
        Reporter:  carter            |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  high              |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:  invalid           |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by bgamari):

 * status:  new => closed
 * resolution:   => invalid


Comment:

 Right, because, just as the error says, that INLINE doesn't correspond to
 any particular in-scope binding. However, you should not need an INLINE
 here; instead just place one on the default definition. You can test this
 yourself with the following,
 {{{#!hs
 module Class where

 class AClass a where
     aList :: a -> [Int]
     aList _ = [1,2,3]
     {-# INLINE aList #-}
 }}}
 {{{#!hs
 module Instance where

 import Class

 instance AClass Int where
 }}}
 {{{#!hs
 module Use where

 import Class
 import Instance

 n :: Int
 n = 42

 main :: IO ()
 main = print (aList n)
 }}}

 If you build `Use` with `-O -ddump-simpl` you will see that the RHS of
 `aList` has been inlined.

 I suspect the real bug here is the fact that this wasn't warned about
 previously. I'll try to draw attention to this change in the release
 notes.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12027#comment:2>
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