[GHC] #9576: -fdefer-type-errors doesn't defer errors from `deriving`

11 Sep 2014

      #9576: -fdefer-type-errors doesn't defer errors from `deriving`
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       Reporter:  goldfire           |                   Owner:
           Type:  bug                |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Compiler           |                 Version:  7.8.3
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:
     Blocked By:                     |  None/Unknown
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
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 When I say

 {{{#!hs
 {-# OPTIONS_GHC -fdefer-type-errors #-}

 data Foo = MkFoo
 data Bar = MkBar Foo
   deriving Show
 }}}

 I get a type error that there is no instance for `Show Foo`. This error
 should be deferred.

 Using standalone-deriving works just fine, though.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9576
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